圖片載入器在Android的App中可謂是重中之重，幾乎任何一款APP都缺少不了圖片，而圖片可以使一個APP具有更豐富的內容，同時反應一個APP具有更加友好的使用者體驗。一般使用的圖片都需要到網路上拉去回來，這就需要圖片載入器了。
一個好的圖片載入器能夠不影響APP效能，同時也應具有以下功能：
1、圖片的同步載入和非同步載入
2、圖片壓縮
3、記憶體快取和磁碟快取
4、網路拉取
從以上的功能特點得出，打造一個優秀的圖片載入器，需要的Bitmap、網路和圖片快取知識等等。
接下來我們一邊打造圖片載入器一邊講解Android的快取策略。
定義快取介面
public interface ImageCache
{
public void setCache(String key,Bitmap bitmap);
public Bitmap getCache(String key,int reqWidth, int reqHeight);
}
複製程式碼該介面功能很簡單：
1）根據key，設定bitmap的快取；
2）根據key，獲取指定大小的bitmap快取。
實現記憶體快取
Android中常用的快取演算法就是LRU（Least Recently Used），即近期最少使用演算法。LRU演算法有兩種：LruCache和DiskLruCache，而記憶體快取使用LruCache。
LruCache是Android3.1提供的一個快取類，通過support-v4相容包，可以相容到Android2.2版本。
import android.graphics.Bitmap;
import android.support.v4.util.LruCache;
public class MemoryCache implements ImageCache
{
private LruCache<String, Bitmap> mMemoryCache;
public MemoryCache()
{
initImageCache();
}
private void initImageCache()
{
//計算可使用的最大記憶體
int maxSize = (int)(Runtime.getRuntime().maxMemory() / 1024);
int cacheSize = maxSize / 8;
mMemoryCache = new LruCache<String, Bitmap>(cacheSize){
@Override
protected int sizeOf(String key, Bitmap value)
{
return value.getRowBytes() * value.getHeight() /1024;
}
};
}
@Override
public void setCache(String url, Bitmap bitmap)
{
String key = BitmapUtils.hashKeyFormUrl(url);
if(mMemoryCache.get(key) == null){
mMemoryCache.put(key, bitmap);
}
}
@Override
public Bitmap getCache(String url, int reqWidth, int reqHeight)
{
String key = BitmapUtils.hashKeyFormUrl(url);
return mMemoryCache.get(key);
}
}
複製程式碼為了相容到Android2.2版本，這裡我使用support-v4包下的LruCache。使用LruCache需要重寫sizeOf方法，該方法的作用是計算快取物件的大小，而且這裡的大小的單位需要和總容量的單位一致，這裡使用記憶體的1/8，單位是KB，sizeOf完成了Bitmap物件的大小計算。除了sizeOf方法，一些特殊情況下需要重寫entryRemove方法，LruCache移除舊快取時，會呼叫entryRemove方法，可以在該方法做一些回收工作。
該類要實現ImageCache介面，在實現的介面方法中實現設定快取和獲取快取的工作即可，同時需要獲取圖片所對應的key，之所以將圖片的url轉成key，是因為圖片url中可能有特殊字元，避免url在Android中的使用。
Bitmap工具類
BitmapUtils工具類
public class BitmapUtils
{
/**
* 獲取縮放後的本地圖片
* @param res
* @param resId
* @param reqW
* @param reqH
* @return
*/
public static Bitmap decodeBitmapFormResource(Resources res, int resId, int reqW, int reqH)
{
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(res, resId, options);
options.inSampleSize = calculateInSampleSize(options, reqW, reqH);
options.inJustDecodeBounds = false;
return BitmapFactory.decodeResource(res, resId, options);
}
/**
* 根據需要的大小動態獲取insampleSize的值
*
* @param options
* @param reqW
* @param reqH
* @return
*/
private static int calculateInSampleSize(BitmapFactory.Options options, int reqW, int reqH)
{
int inSampleSize = 1;
if(reqH == 0 || reqW == 0)
{
return inSampleSize;
}
int outW = options.outWidth;
int outH = options.outHeight;
if(outW > reqW || outH > reqH)
{
int halfW = outW / 2;
int halfH = outH / 2;
while((halfH / inSampleSize) >= reqH && (halfW / inSampleSize) >= reqW)
{
inSampleSize *= 2;
}
}
return inSampleSize;
}
/**
* MD5
* 將url轉化成key
* @param url
* @return
*/
public static String hashKeyFormUrl(String url)
{
String cacheKey;
try
{
final MessageDigest mDigest = MessageDigest.getInstance("MD5");
mDigest.update(url.getBytes());
cacheKey = bytesToHexString(mDigest.digest());
}
catch(NoSuchAlgorithmException e)
{
cacheKey = String.valueOf(url.hashCode());
}
return cacheKey;
}
private static String bytesToHexString(byte[] bytes)
{
StringBuilder sb = new StringBuilder();
for(int i = 0; i < bytes.length; i++)
{
String hex = Integer.toHexString(0xFF & bytes[i]);
if(hex.length() == 1)
{
sb.append('0');
}
sb.append(hex);
}
return sb.toString();
}
/**
* DiskLruCaceh
* 獲取縮放後的bitmap
* @param fd
* @param reqWidth
* @param reqHeight
* @return
*/
public static Bitmap decodeSampledBitmapFromFileDescriptor(FileDescriptor fd, int reqWidth, int reqHeight)
{
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFileDescriptor(fd, null, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeFileDescriptor(fd, null, options);
}
}
複製程式碼注意：
1）hashKeyFormUrl方法是採用url的md5值作為key
2）decodeSampledBitmapFromFileDescriptor方法：由於FileInputStream是一種有序的檔案流，而兩次decodeStream呼叫會影響檔案流的位置屬性，導致第二次decodeStream時得到的是null，因此需要通過檔案流來得到它所對應檔案描述符，然後通過BitmapFactory.decodeFileDescriptor來載入一張縮放後的圖片。
3）高效載入圖片就是採用BitmapFactory.Options來載入所需要的尺寸圖片，而Options來縮放圖片，主要是通過inSampleSize引數，也就是取樣率，方法比例為：
縮放比例 = 1/（inSampleSize的2的次方）
如一張ARGB8888的10241024圖片原來大小為102410244，也就是4M，當inSampleSize = 2時，變為512512*4，也就是1M。
磁碟快取實現
DiskLruCache是用於實現儲存裝置快取，也就是磁碟快取，它通過快取物件寫入檔案系統從而實習快取的效果。
但DiskLruCache並不屬於Android SDK，其原始碼地址：
https://android.googlesource.com/platform/libcore/+/android-4.1.1_r1/luni/src/main/java/libcore/io/DiskLruCache.java
DiskCache ：
/**
*
* DiskLruCache磁碟快取，它不屬於Android sdk的一部分
* 它的原始碼可以在這裡下載 DiskLruCache的建立、快取查詢和快取新增操作
* https://android.googlesource.com/platform/libcore/+/android-4.1.1_r1/luni/src/main/java/libcore/io/DiskLruCache.java
*/
public class DiskCache implements ImageCache
{
private static final long DISK_CACHE_SIZE = 1024 * 1024 * 50;
private DiskLruCache mDiskLruCache;
// static String cacheDir = "sdcard/myapplication/cache/";
private boolean mIsDiskLruCacheCreated = false;
private static final String TAG = "ImageLoader";
private static final int DISK_CACHE_INDEX = 0;
private static final int IO_BUFFER_SIZE = 8 * 1024;
/**
* 是否需要磁碟快取
* @return
*/
public boolean isDiskLruCacheCreated()
{
return mIsDiskLruCacheCreated;
}
/**
* 設定是否需要磁碟快取
* @param diskLruCacheCreated
*/
public void setDiskLruCacheCreated(boolean diskLruCacheCreated)
{
mIsDiskLruCacheCreated = diskLruCacheCreated;
}
public DiskCache(Context context)
{
initCache(context);
}
/**
* 初始化磁碟快取
* @param context
*/
private void initCache(Context context)
{
File file = getDiskCacheDir(context,"myapplication/cache");
if(!file.exists())
{
file.mkdirs();
}
try
{
mDiskLruCache = DiskLruCache.open(file, 1, 1, DISK_CACHE_SIZE);
mIsDiskLruCacheCreated = true;
}
catch(IOException e)
{
e.printStackTrace();
}
}
private long getUsableSpace(File path)
{
if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.GINGERBREAD)
{
return path.getUsableSpace();
}
final StatFs stats = new StatFs(path.getPath());
return (long)stats.getBlockSize() * (long)stats.getAvailableBlocks();
}
/**
* 獲取快取路徑
* @param context
* @param uniqueName
* @return
*/
private File getDiskCacheDir(Context context, String uniqueName)
{
// String path = getSdcardPath() + cacheDir;
// return new File(path);
boolean externalStorageAvailable = Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED);
final String cachePath;
if(externalStorageAvailable)
{
cachePath = context.getExternalCacheDir().getPath();
}
else
{
cachePath = context.getCacheDir().getPath();
}
return new File(cachePath + File.separator + uniqueName);
}
/**
* 獲取sdcard路徑
* @return
*/
public static String getSdcardPath()
{
File sdcard = Environment.getExternalStorageDirectory();
if(sdcard == null)
{
return "";
}
return sdcard.getPath();
}
/**
* 設定bitmap快取
* @param url
* @param bitmap
*/
@Override
public void setCache(String url, Bitmap bitmap)
{
String key = BitmapUtils.hashKeyFormUrl(url);
try
{
DiskLruCache.Editor editor = mDiskLruCache.edit(key);
if(editor != null)
{
OutputStream outputStream = editor.newOutputStream(DISK_CACHE_INDEX);
if(downloadUrlToStream(url, outputStream))
{
editor.commit();
}
else
{
editor.abort();
}
mDiskLruCache.flush();
}
}
catch(IOException e)
{
e.printStackTrace();
}
}
/**
* 將圖片下載寫到磁碟
*
* @param urlString
* @param outputStream
* @return
*/
private boolean downloadUrlToStream(String urlString, OutputStream outputStream)
{
HttpURLConnection urlConnection = null;
BufferedOutputStream out = null;
BufferedInputStream in = null;
try
{
final URL url = new URL(urlString);
urlConnection = (HttpURLConnection)url.openConnection();
in = new BufferedInputStream(urlConnection.getInputStream(), IO_BUFFER_SIZE);
out = new BufferedOutputStream(outputStream, IO_BUFFER_SIZE);
int b;
while((b = in.read()) != -1)
{
out.write(b);
}
return true;
}
catch(IOException e)
{
Log.e(TAG, "downloadBitmap failed." + e);
}
finally
{
if(urlConnection != null)
{
urlConnection.disconnect();
}
MyUtils.close(out);
MyUtils.close(in);
}
return false;
}
/**
* 獲取bitmap快取
* @param url
* @param reqWidth
* @param reqHeight
* @return
*/
@Override
public Bitmap getCache(String url, int reqWidth, int reqHeight)
{
Bitmap bitmap = null;
String key = BitmapUtils.hashKeyFormUrl(url);
try
{
if(!TextUtils.isEmpty(key))
{
DiskLruCache.Snapshot snapShot = mDiskLruCache.get(key);
if(snapShot != null)
{
FileInputStream fileInputStream = (FileInputStream)snapShot.getInputStream(DISK_CACHE_INDEX);
FileDescriptor fileDescriptor = fileInputStream.getFD();
bitmap = BitmapUtils.decodeSampledBitmapFromFileDescriptor(fileDescriptor, reqWidth, reqHeight);
}
}
}
catch(IOException e)
{
e.printStackTrace();
}
return bitmap;
}
}
複製程式碼open(File directory, int appVersion, int valueCount, long maxSize)： directory：磁碟快取在檔案系統中的儲存路徑。快取路徑可以選sdcard的快取路徑（/sdcard/Android/data/pachkage_name/cache）目錄，此目錄應用解除安裝會被刪除，當然也可以指定其他目錄。 appVersion：版本號，一般設定1即可 valueCount：單個節點所對應的資料個數，一般設定1即可 maxSize：快取總大小
downloadUrlToStream方法：該方法並沒有真正的將圖片寫入檔案系統，還需要通過setCache方法的Editor的commit方法來提交寫入操作，如果圖片下載過程發生了異常，還可以通過Editor的abort方法回退整個操作。
該類同樣需要實現ImageCache來實現設定快取和獲取快取。
DiskLruCache原始碼
/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.io.BufferedInputStream;
import java.io.BufferedWriter;
import java.io.Closeable;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.StringWriter;
import java.io.Writer;
import java.lang.reflect.Array;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
/**
* *****************************************************************************
* Taken from the JB source code, can be found in:
* libcore/luni/src/main/java/libcore/io/DiskLruCache.java
* or direct link:
* https://android.googlesource.com/platform/libcore/+/android-4.1.1_r1/luni/src/main/java/libcore/io/DiskLruCache.java
* *****************************************************************************
* <p>
* A cache that uses a bounded amount of space on a filesystem. Each cache
* entry has a string key and a fixed number of values. Values are byte
* sequences, accessible as streams or files. Each value must be between {@code
* 0} and {@code Integer.MAX_VALUE} bytes in length.
* <p>
* <p>The cache stores its data in a directory on the filesystem. This
* directory must be exclusive to the cache; the cache may delete or overwrite
* files from its directory. It is an error for multiple processes to use the
* same cache directory at the same time.
* <p>
* <p>This cache limits the number of bytes that it will store on the
* filesystem. When the number of stored bytes exceeds the limit, the cache will
* remove entries in the background until the limit is satisfied. The limit is
* not strict: the cache may temporarily exceed it while waiting for files to be
* deleted. The limit does not include filesystem overhead or the cache
* journal so space-sensitive applications should set a conservative limit.
* <p>
* <p>Clients call {@link #edit} to create or update the values of an entry. An
* entry may have only one editor at one time; if a value is not available to be
* edited then {@link #edit} will return null.
* <ul>
* <li>When an entry is being <strong>created</strong> it is necessary to
* supply a full set of values; the empty value should be used as a
* placeholder if necessary.
* <li>When an entry is being <strong>edited</strong>, it is not necessary
* to supply data for every value; values default to their previous
* value.
* </ul>
* Every {@link #edit} call must be matched by a call to {@link Editor#commit}
* or {@link Editor#abort}. Committing is atomic: a read observes the full set
* of values as they were before or after the commit, but never a mix of values.
* <p>
* <p>Clients call {@link #get} to read a snapshot of an entry. The read will
* observe the value at the time that {@link #get} was called. Updates and
* removals after the call do not impact ongoing reads.
* <p>
* <p>This class is tolerant of some I/O errors. If files are missing from the
* filesystem, the corresponding entries will be dropped from the cache. If
* an error occurs while writing a cache value, the edit will fail silently.
* Callers should handle other problems by catching {@code IOException} and
* responding appropriately.
* 磁碟快取
*/
public final class DiskLruCache implements Closeable
{
static final String JOURNAL_FILE = "journal";
static final String JOURNAL_FILE_TMP = "journal.tmp";
static final String MAGIC = "libcore.io.DiskLruCache";
static final String VERSION_1 = "1";
static final long ANY_SEQUENCE_NUMBER = -1;
private static final String CLEAN = "CLEAN";
private static final String DIRTY = "DIRTY";
private static final String REMOVE = "REMOVE";
private static final String READ = "READ";
private static final Charset UTF_8 = Charset.forName("UTF-8");
private static final int IO_BUFFER_SIZE = 8 * 1024;
/*
* This cache uses a journal file named "journal". A typical journal file
* looks like this:
* libcore.io.DiskLruCache
* 1
* 100
* 2
*
* CLEAN 3400330d1dfc7f3f7f4b8d4d803dfcf6 832 21054
* DIRTY 335c4c6028171cfddfbaae1a9c313c52
* CLEAN 335c4c6028171cfddfbaae1a9c313c52 3934 2342
* REMOVE 335c4c6028171cfddfbaae1a9c313c52
* DIRTY 1ab96a171faeeee38496d8b330771a7a
* CLEAN 1ab96a171faeeee38496d8b330771a7a 1600 234
* READ 335c4c6028171cfddfbaae1a9c313c52
* READ 3400330d1dfc7f3f7f4b8d4d803dfcf6
*
* The first five lines of the journal form its header. They are the
* constant string "libcore.io.DiskLruCache", the disk cache's version,
* the application's version, the value count, and a blank line.
*
* Each of the subsequent lines in the file is a record of the state of a
* cache entry. Each line contains space-separated values: a state, a key,
* and optional state-specific values.
* o DIRTY lines track that an entry is actively being created or updated.
* Every successful DIRTY action should be followed by a CLEAN or REMOVE
* action. DIRTY lines without a matching CLEAN or REMOVE indicate that
* temporary files may need to be deleted.
* o CLEAN lines track a cache entry that has been successfully published
* and may be read. A publish line is followed by the lengths of each of
* its values.
* o READ lines track accesses for LRU.
* o REMOVE lines track entries that have been deleted.
*
* The journal file is appended to as cache operations occur. The journal may
* occasionally be compacted by dropping redundant lines. A temporary file named
* "journal.tmp" will be used during compaction; that file should be deleted if
* it exists when the cache is opened.
*/
private final File directory;
private final File journalFile;
private final File journalFileTmp;
private final int appVersion;
private final long maxSize;
private final int valueCount;
private long size = 0;
private Writer journalWriter;
private final LinkedHashMap<String, Entry> lruEntries = new LinkedHashMap<String, Entry>(0, 0.75f, true);
private int redundantOpCount;
/**
* To differentiate between old and current snapshots, each entry is given
* a sequence number each time an edit is committed. A snapshot is stale if
* its sequence number is not equal to its entry's sequence number.
*/
private long nextSequenceNumber = 0;
/* From java.util.Arrays */
@SuppressWarnings("unchecked")
private static <T> T[] copyOfRange(T[] original, int start, int end)
{
final int originalLength = original.length; // For exception priority compatibility.
if(start > end)
{
throw new IllegalArgumentException();
}
if(start < 0 || start > originalLength)
{
throw new ArrayIndexOutOfBoundsException();
}
final int resultLength = end - start;
final int copyLength = Math.min(resultLength, originalLength - start);
final T[] result = (T[])Array.newInstance(original.getClass().getComponentType(), resultLength);
System.arraycopy(original, start, result, 0, copyLength);
return result;
}
/**
* Returns the remainder of 'reader' as a string, closing it when done.
*/
public static String readFully(Reader reader) throws IOException
{
try
{
StringWriter writer = new StringWriter();
char[] buffer = new char[1024];
int count;
while((count = reader.read(buffer)) != -1)
{
writer.write(buffer, 0, count);
}
return writer.toString();
}
finally
{
reader.close();
}
}
/**
* Returns the ASCII characters up to but not including the next "\r\n", or
* "\n".
*
* @throws EOFException if the stream is exhausted before the next newline
* character.
*/
public static String readAsciiLine(InputStream in) throws IOException
{
// TODO: support UTF-8 here instead
StringBuilder result = new StringBuilder(80);
while(true)
{
int c = in.read();
if(c == -1)
{
throw new EOFException();
}
else if(c == '\n')
{
break;
}
result.append((char)c);
}
int length = result.length();
if(length > 0 && result.charAt(length - 1) == '\r')
{
result.setLength(length - 1);
}
return result.toString();
}
/**
* Closes 'closeable', ignoring any checked exceptions. Does nothing if 'closeable' is null.
*/
public static void closeQuietly(Closeable closeable)
{
if(closeable != null)
{
try
{
closeable.close();
}
catch(RuntimeException rethrown)
{
throw rethrown;
}
catch(Exception ignored)
{
}
}
}
/**
* Recursively delete everything in {@code dir}.
*/
// TODO: this should specify paths as Strings rather than as Files
public static void deleteContents(File dir) throws IOException
{
File[] files = dir.listFiles();
if(files == null)
{
throw new IllegalArgumentException("not a directory: " + dir);
}
for(File file : files)
{
if(file.isDirectory())
{
deleteContents(file);
}
if(!file.delete())
{
throw new IOException("failed to delete file: " + file);
}
}
}
/**
* This cache uses a single background thread to evict entries.
*/
private final ExecutorService executorService = new ThreadPoolExecutor(0, 1, 60L, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
private final Callable<Void> cleanupCallable = new Callable<Void>()
{
@Override
public Void call() throws Exception
{
synchronized(DiskLruCache.this)
{
if(journalWriter == null)
{
return null; // closed
}
trimToSize();
if(journalRebuildRequired())
{
rebuildJournal();
redundantOpCount = 0;
}
}
return null;
}
};
private DiskLruCache(File directory, int appVersion, int valueCount, long maxSize)
{
this.directory = directory;
this.appVersion = appVersion;
this.journalFile = new File(directory, JOURNAL_FILE);
this.journalFileTmp = new File(directory, JOURNAL_FILE_TMP);
this.valueCount = valueCount;
this.maxSize = maxSize;
}
/**
* Opens the cache in {@code directory}, creating a cache if none exists
* there.
*
* @param directory a writable directory
* @param appVersion
* @param valueCount the number of values per cache entry. Must be positive.
* @param maxSize the maximum number of bytes this cache should use to store
* @throws IOException if reading or writing the cache directory fails
*/
public static DiskLruCache open(File directory, int appVersion, int valueCount, long maxSize) throws IOException
{
if(maxSize <= 0)
{
throw new IllegalArgumentException("maxSize <= 0");
}
if(valueCount <= 0)
{
throw new IllegalArgumentException("valueCount <= 0");
}
// prefer to pick up where we left off
DiskLruCache cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
if(cache.journalFile.exists())
{
try
{
cache.readJournal();
cache.processJournal();
cache.journalWriter = new BufferedWriter(new FileWriter(cache.journalFile, true), IO_BUFFER_SIZE);
return cache;
}
catch(IOException journalIsCorrupt)
{
// System.logW("DiskLruCache " + directory + " is corrupt: "
// + journalIsCorrupt.getMessage() + ", removing");
cache.delete();
}
}
// create a new empty cache
directory.mkdirs();
cache = new DiskLruCache(directory, appVersion, valueCount, maxSize);
cache.rebuildJournal();
return cache;
}
private void readJournal() throws IOException
{
InputStream in = new BufferedInputStream(new FileInputStream(journalFile), IO_BUFFER_SIZE);
try
{
String magic = readAsciiLine(in);
String version = readAsciiLine(in);
String appVersionString = readAsciiLine(in);
String valueCountString = readAsciiLine(in);
String blank = readAsciiLine(in);
if(!MAGIC.equals(magic) || !VERSION_1.equals(version) || !Integer.toString(appVersion).equals(appVersionString) || !Integer.toString(valueCount).equals(valueCountString) || !"".equals(blank))
{
throw new IOException("unexpected journal header: [" + magic + ", " + version + ", " + valueCountString + ", " + blank + "]");
}
while(true)
{
try
{
readJournalLine(readAsciiLine(in));
}
catch(EOFException endOfJournal)
{
break;
}
}
}
finally
{
closeQuietly(in);
}
}
private void readJournalLine(String line) throws IOException
{
String[] parts = line.split(" ");
if(parts.length < 2)
{
throw new IOException("unexpected journal line: " + line);
}
String key = parts[1];
if(parts[0].equals(REMOVE) && parts.length == 2)
{
lruEntries.remove(key);
return;
}
Entry entry = lruEntries.get(key);
if(entry == null)
{
entry = new Entry(key);
lruEntries.put(key, entry);
}
if(parts[0].equals(CLEAN) && parts.length == 2 + valueCount)
{
entry.readable = true;
entry.currentEditor = null;
entry.setLengths(copyOfRange(parts, 2, parts.length));
}
else if(parts[0].equals(DIRTY) && parts.length == 2)
{
entry.currentEditor = new Editor(entry);
}
else if(parts[0].equals(READ) && parts.length == 2)
{
// this work was already done by calling lruEntries.get()
}
else
{
throw new IOException("unexpected journal line: " + line);
}
}
/**
* Computes the initial size and collects garbage as a part of opening the
* cache. Dirty entries are assumed to be inconsistent and will be deleted.
*/
private void processJournal() throws IOException
{
deleteIfExists(journalFileTmp);
for(Iterator<Entry> i = lruEntries.values().iterator(); i.hasNext(); )
{
Entry entry = i.next();
if(entry.currentEditor == null)
{
for(int t = 0; t < valueCount; t++)
{
size += entry.lengths[t];
}
}
else
{
entry.currentEditor = null;
for(int t = 0; t < valueCount; t++)
{
deleteIfExists(entry.getCleanFile(t));
deleteIfExists(entry.getDirtyFile(t));
}
i.remove();
}
}
}
/**
* Creates a new journal that omits redundant information. This replaces the
* current journal if it exists.
*/
private synchronized void rebuildJournal() throws IOException
{
if(journalWriter != null)
{
journalWriter.close();
}
Writer writer = new BufferedWriter(new FileWriter(journalFileTmp), IO_BUFFER_SIZE);
writer.write(MAGIC);
writer.write("\n");
writer.write(VERSION_1);
writer.write("\n");
writer.write(Integer.toString(appVersion));
writer.write("\n");
writer.write(Integer.toString(valueCount));
writer.write("\n");
writer.write("\n");
for(Entry entry : lruEntries.values())
{
if(entry.currentEditor != null)
{
writer.write(DIRTY + ' ' + entry.key + '\n');
}
else
{
writer.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');
}
}
writer.close();
journalFileTmp.renameTo(journalFile);
journalWriter = new BufferedWriter(new FileWriter(journalFile, true), IO_BUFFER_SIZE);
}
private static void deleteIfExists(File file) throws IOException
{
// try {
// Libcore.os.remove(file.getPath());
// } catch (ErrnoException errnoException) {
// if (errnoException.errno != OsConstants.ENOENT) {
// throw errnoException.rethrowAsIOException();
// }
// }
if(file.exists() && !file.delete())
{
throw new IOException();
}
}
/**
* Returns a snapshot of the entry named {@code key}, or null if it doesn't
* exist is not currently readable. If a value is returned, it is moved to
* the head of the LRU queue.
*/
public synchronized Snapshot get(String key) throws IOException
{
checkNotClosed();
validateKey(key);
Entry entry = lruEntries.get(key);
if(entry == null)
{
return null;
}
if(!entry.readable)
{
return null;
}
/*
* Open all streams eagerly to guarantee that we see a single published
* snapshot. If we opened streams lazily then the streams could come
* from different edits.
*/
InputStream[] ins = new InputStream[valueCount];
try
{
for(int i = 0; i < valueCount; i++)
{
ins[i] = new FileInputStream(entry.getCleanFile(i));
}
}
catch(FileNotFoundException e)
{
// a file must have been deleted manually!
return null;
}
redundantOpCount++;
journalWriter.append(READ + ' ' + key + '\n');
if(journalRebuildRequired())
{
executorService.submit(cleanupCallable);
}
return new Snapshot(key, entry.sequenceNumber, ins);
}
/**
* Returns an editor for the entry named {@code key}, or null if another
* edit is in progress.
*/
public Editor edit(String key) throws IOException
{
return edit(key, ANY_SEQUENCE_NUMBER);
}
private synchronized Editor edit(String key, long expectedSequenceNumber) throws IOException
{
checkNotClosed();
validateKey(key);
Entry entry = lruEntries.get(key);
if(expectedSequenceNumber != ANY_SEQUENCE_NUMBER && (entry == null || entry.sequenceNumber != expectedSequenceNumber))
{
return null; // snapshot is stale
}
if(entry == null)
{
entry = new Entry(key);
lruEntries.put(key, entry);
}
else if(entry.currentEditor != null)
{
return null; // another edit is in progress
}
Editor editor = new Editor(entry);
entry.currentEditor = editor;
// flush the journal before creating files to prevent file leaks
journalWriter.write(DIRTY + ' ' + key + '\n');
journalWriter.flush();
return editor;
}
/**
* Returns the directory where this cache stores its data.
*/
public File getDirectory()
{
return directory;
}
/**
* Returns the maximum number of bytes that this cache should use to store
* its data.
*/
public long maxSize()
{
return maxSize;
}
/**
* Returns the number of bytes currently being used to store the values in
* this cache. This may be greater than the max size if a background
* deletion is pending.
*/
public synchronized long size()
{
return size;
}
private synchronized void completeEdit(Editor editor, boolean success) throws IOException
{
Entry entry = editor.entry;
if(entry.currentEditor != editor)
{
throw new IllegalStateException();
}
// if this edit is creating the entry for the first time, every index must have a value
if(success && !entry.readable)
{
for(int i = 0; i < valueCount; i++)
{
if(!entry.getDirtyFile(i).exists())
{
editor.abort();
throw new IllegalStateException("edit didn't create file " + i);
}
}
}
for(int i = 0; i < valueCount; i++)
{
File dirty = entry.getDirtyFile(i);
if(success)
{
if(dirty.exists())
{
File clean = entry.getCleanFile(i);
dirty.renameTo(clean);
long oldLength = entry.lengths[i];
long newLength = clean.length();
entry.lengths[i] = newLength;
size = size - oldLength + newLength;
}
}
else
{
deleteIfExists(dirty);
}
}
redundantOpCount++;
entry.currentEditor = null;
if(entry.readable | success)
{
entry.readable = true;
journalWriter.write(CLEAN + ' ' + entry.key + entry.getLengths() + '\n');
if(success)
{
entry.sequenceNumber = nextSequenceNumber++;
}
}
else
{
lruEntries.remove(entry.key);
journalWriter.write(REMOVE + ' ' + entry.key + '\n');
}
if(size > maxSize || journalRebuildRequired())
{
executorService.submit(cleanupCallable);
}
}
/**
* We only rebuild the journal when it will halve the size of the journal
* and eliminate at least 2000 ops.
*/
private boolean journalRebuildRequired()
{
final int REDUNDANT_OP_COMPACT_THRESHOLD = 2000;
return redundantOpCount >= REDUNDANT_OP_COMPACT_THRESHOLD && redundantOpCount >= lruEntries.size();
}
/**
* Drops the entry for {@code key} if it exists and can be removed. Entries
* actively being edited cannot be removed.
*
* @return true if an entry was removed.
*/
public synchronized boolean remove(String key) throws IOException
{
checkNotClosed();
validateKey(key);
Entry entry = lruEntries.get(key);
if(entry == null || entry.currentEditor != null)
{
return false;
}
for(int i = 0; i < valueCount; i++)
{
File file = entry.getCleanFile(i);
if(!file.delete())
{
throw new IOException("failed to delete " + file);
}
size -= entry.lengths[i];
entry.lengths[i] = 0;
}
redundantOpCount++;
journalWriter.append(REMOVE + ' ' + key + '\n');
lruEntries.remove(key);
if(journalRebuildRequired())
{
executorService.submit(cleanupCallable);
}
return true;
}
/**
* Returns true if this cache has been closed.
*/
public boolean isClosed()
{
return journalWriter == null;
}
private void checkNotClosed()
{
if(journalWriter == null)
{
throw new IllegalStateException("cache is closed");
}
}
/**
* Force buffered operations to the filesystem.
*/
public synchronized void flush() throws IOException
{
checkNotClosed();
trimToSize();
journalWriter.flush();
}
/**
* Closes this cache. Stored values will remain on the filesystem.
*/
public synchronized void close() throws IOException
{
if(journalWriter == null)
{
return; // already closed
}
for(Entry entry : new ArrayList<Entry>(lruEntries.values()))
{
if(entry.currentEditor != null)
{
entry.currentEditor.abort();
}
}
trimToSize();
journalWriter.close();
journalWriter = null;
}
private void trimToSize() throws IOException
{
while(size > maxSize)
{
// Map.Entry<String, Entry> toEvict = lruEntries.eldest();
final Map.Entry<String, Entry> toEvict = lruEntries.entrySet().iterator().next();
remove(toEvict.getKey());
}
}
/**
* Closes the cache and deletes all of its stored values. This will delete
* all files in the cache directory including files that weren't created by
* the cache.
*/
public void delete() throws IOException
{
close();
deleteContents(directory);
}
private void validateKey(String key)
{
if(key.contains(" ") || key.contains("\n") || key.contains("\r"))
{
throw new IllegalArgumentException("keys must not contain spaces or newlines: \"" + key + "\"");
}
}
private static String inputStreamToString(InputStream in) throws IOException
{
return readFully(new InputStreamReader(in, UTF_8));
}
/**
* A snapshot of the values for an entry.
*/
public final class Snapshot implements Closeable
{
private final String key;
private final long sequenceNumber;
private final InputStream[] ins;
private Snapshot(String key, long sequenceNumber, InputStream[] ins)
{
this.key = key;
this.sequenceNumber = sequenceNumber;
this.ins = ins;
}
/**
* Returns an editor for this snapshot's entry, or null if either the
* entry has changed since this snapshot was created or if another edit
* is in progress.
*/
public Editor edit() throws IOException
{
return DiskLruCache.this.edit(key, sequenceNumber);
}
/**
* Returns the unbuffered stream with the value for {@code index}.
*/
public InputStream getInputStream(int index)
{
return ins[index];
}
/**
* Returns the string value for {@code index}.
*/
public String getString(int index) throws IOException
{
return inputStreamToString(getInputStream(index));
}
@Override
public void close()
{
for(InputStream in : ins)
{
closeQuietly(in);
}
}
}
/**
* Edits the values for an entry.
*/
public final class Editor
{
private final Entry entry;
private boolean hasErrors;
private Editor(Entry entry)
{
this.entry = entry;
}
/**
* Returns an unbuffered input stream to read the last committed value,
* or null if no value has been committed.
*/
public InputStream newInputStream(int index) throws IOException
{
synchronized(DiskLruCache.this)
{
if(entry.currentEditor != this)
{
throw new IllegalStateException();
}
if(!entry.readable)
{
return null;
}
return new FileInputStream(entry.getCleanFile(index));
}
}
/**
* Returns the last committed value as a string, or null if no value
* has been committed.
*/
public String getString(int index) throws IOException
{
InputStream in = newInputStream(index);
return in != null ? inputStreamToString(in) : null;
}
/**
* Returns a new unbuffered output stream to write the value at
* {@code index}. If the underlying output stream encounters errors
* when writing to the filesystem, this edit will be aborted when
* {@link #commit} is called. The returned output stream does not throw
* IOExceptions.
*/
public OutputStream newOutputStream(int index) throws IOException
{
synchronized(DiskLruCache.this)
{
if(entry.currentEditor != this)
{
throw new IllegalStateException();
}
return new FaultHidingOutputStream(new FileOutputStream(entry.getDirtyFile(index)));
}
}
/**
* Sets the value at {@code index} to {@code value}.
*/
public void set(int index, String value) throws IOException
{
Writer writer = null;
try
{
writer = new OutputStreamWriter(newOutputStream(index), UTF_8);
writer.write(value);
}
finally
{
closeQuietly(writer);
}
}
/**
* Commits this edit so it is visible to readers. This releases the
* edit lock so another edit may be started on the same key.
*/
public void commit() throws IOException
{
if(hasErrors)
{
completeEdit(this, false);
remove(entry.key); // the previous entry is stale
}
else
{
completeEdit(this, true);
}
}
/**
* Aborts this edit. This releases the edit lock so another edit may be
* started on the same key.
*/
public void abort() throws IOException
{
completeEdit(this, false);
}
private class FaultHidingOutputStream extends FilterOutputStream
{
private FaultHidingOutputStream(OutputStream out)
{
super(out);
}
@Override
public void write(int oneByte)
{
try
{
out.write(oneByte);
}
catch(IOException e)
{
hasErrors = true;
}
}
@Override
public void write(byte[] buffer, int offset, int length)
{
try
{
out.write(buffer, offset, length);
}
catch(IOException e)
{
hasErrors = true;
}
}
@Override
public void close()
{
try
{
out.close();
}
catch(IOException e)
{
hasErrors = true;
}
}
@Override
public void flush()
{
try
{
out.flush();
}
catch(IOException e)
{
hasErrors = true;
}
}
}
}
private final class Entry
{
private final String key;
/**
* Lengths of this entry's files.
*/
private final long[] lengths;
/**
* True if this entry has ever been published
*/
private boolean readable;
/**
* The ongoing edit or null if this entry is not being edited.
*/
private Editor currentEditor;
/**
* The sequence number of the most recently committed edit to this entry.
*/
private long sequenceNumber;
private Entry(String key)
{
this.key = key;
this.lengths = new long[valueCount];
}
public String getLengths() throws IOException
{
StringBuilder result = new StringBuilder();
for(long size : lengths)
{
result.append(' ').append(size);
}
return result.toString();
}
/**
* Set lengths using decimal numbers like "10123".
*/
private void setLengths(String[] strings) throws IOException
{
if(strings.length != valueCount)
{
throw invalidLengths(strings);
}
try
{
for(int i = 0; i < strings.length; i++)
{
lengths[i] = Long.parseLong(strings[i]);
}
}
catch(NumberFormatException e)
{
throw invalidLengths(strings);
}
}
private IOException invalidLengths(String[] strings) throws IOException
{
throw new IOException("unexpected journal line: " + Arrays.toString(strings));
}
public File getCleanFile(int i)
{
return new File(directory, key + "." + i);
}
public File getDirtyFile(int i)
{
return new File(directory, key + "." + i + ".tmp");
}
}
}
複製程式碼關閉流工具
public class MyUtils
{
/**
* 關閉流
* @param out
*/
public static void close(Closeable out)
{
if(out != null)
{
try
{
out.close();
}
catch(IOException e)
{
e.printStackTrace();
}
}
}
}
複製程式碼該工具中的close方法可以關閉任何流，因為流都實現了Closeable介面的close方法。
ImageLoader實現
ImageLoader：
public class ImageLoader
{
private static final String TAG = "ImageLoader";
private static final int TAG_KEY_URI = R.id.gridview_item_imageview;
private static final int CPU_COUNT = Runtime.getRuntime().availableProcessors();
private static final int CORE_POOL_SIZE = CPU_COUNT + 1;
private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1;
private static final long KEEP_ALIVE = 10L;
private Context mContext;
private MemoryCache mMemoryCache;
private DiskCache mDiskCache;
public static final int MESSAGE_POST_RESULT = 1;
private static final int IO_BUFFER_SIZE = 8 * 1024;
private static final ThreadFactory sThreadFactory = new ThreadFactory()
{
private final AtomicInteger mCount = new AtomicInteger(1);
public Thread newThread(Runnable r)
{
return new Thread(r, "ImageLoader#" + mCount.getAndIncrement());
}
};
/**
* 執行緒池
*/
public static final Executor THREAD_POOL_EXECUTOR = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(), sThreadFactory);
private Handler mMainHandler = new Handler(Looper.getMainLooper())
{
@Override
public void handleMessage(Message msg)
{
LoaderResult result = (LoaderResult)msg.obj;
ImageView imageView = result.imageView;
String uri = (String)imageView.getTag(TAG_KEY_URI);
if(uri.equals(result.uri))
{
imageView.setImageBitmap(result.bitmap);
}
else
{
Log.w(TAG, "set image bitmap,but url has changed, ignored!");
}
}
};
/**
* 初始化物件
* @param context
*/
public ImageLoader(Context context)
{
mDiskCache = new DiskCache(context);
mMemoryCache = new MemoryCache();
this.mContext = context.getApplicationContext();
}
public static ImageLoader build(Context context)
{
return new ImageLoader(context);
}
/**
* 繫結bitmap
*
* @param uri
* @param imageView
*/
public void bindBitmap(String uri, ImageView imageView)
{
bindBitmap(uri, imageView, 0, 0);
}
public void bindBitmap(final String uri, final ImageView imageView, final int reqW, final int reqH)
{
imageView.setTag(TAG_KEY_URI, uri);
Bitmap bitmap = mMemoryCache.getCache(uri, 0, 0);
if(bitmap != null)
{
imageView.setImageBitmap(bitmap);
return;
}
Runnable runnable = new Runnable()
{
@Override
public void run()
{
Bitmap bitmap = loadBitmap(uri, reqW, reqH);
if(bitmap != null)
{
LoaderResult result = new LoaderResult(imageView, uri, bitmap);
// mMainHandler.obtainMessage(MESSAGE_POST_RESULT, result);
Message msg = new Message();
msg.what = MESSAGE_POST_RESULT;
msg.obj = result;
mMainHandler.sendMessage(msg);
}
}
};
THREAD_POOL_EXECUTOR.execute(runnable);
}
/**
* 載入bitmap
* @param uri
* @param reqW
* @param reqH
* @return
*/
private Bitmap loadBitmap(String uri, int reqW, int reqH)
{
Bitmap bitmap = mMemoryCache.getCache(uri, reqW, reqH);
if(bitmap != null)
{
return bitmap;
}
bitmap = mDiskCache.getCache(uri, reqH, reqH);
if(bitmap != null)
{
return bitmap;
}
bitmap = loadBitmapFromHttp(uri, reqW, reqH);
return bitmap;
}
/**
* 從網路獲取bitmap
* @param uri
* @param reqW
* @param reqH
* @return
*/
private Bitmap loadBitmapFromHttp(String uri, int reqW, int reqH)
{
Bitmap bitmap = null;
if(Looper.myLooper() == Looper.getMainLooper())
{
throw new RuntimeException("can not visit network from UI Thread.");
}
if(mDiskCache == null)
{
return null;
}
mDiskCache.setCache(uri, null);
bitmap = mDiskCache.getCache(uri, reqW, reqH);
if(bitmap != null)
{
mMemoryCache.setCache(uri, bitmap);
}
if(bitmap == null && !mDiskCache.isDiskLruCacheCreated())
{
bitmap = downloadBitmapFromUrl(uri);
}
return bitmap;
}
/**
* 載入網路圖片
* @param urlString
* @return
*/
private Bitmap downloadBitmapFromUrl(String urlString)
{
Bitmap bitmap = null;
HttpURLConnection urlConnection = null;
BufferedInputStream in = null;
try
{
final URL url = new URL(urlString);
urlConnection = (HttpURLConnection)url.openConnection();
in = new BufferedInputStream(urlConnection.getInputStream(), IO_BUFFER_SIZE);
bitmap = BitmapFactory.decodeStream(in);
}
catch(final IOException e)
{
Log.e(TAG, "Error in downloadBitmap: " + e);
}
finally
{
if(urlConnection != null)
{
urlConnection.disconnect();
}
MyUtils.close(in);
}
return bitmap;
}
private static class LoaderResult
{
public ImageView imageView;
public String uri;
public Bitmap bitmap;
public LoaderResult(ImageView imageView, String uri, Bitmap bitmap)
{
this.imageView = imageView;
this.uri = uri;
this.bitmap = bitmap;
}
}
}
複製程式碼注意： 1）採用執行緒池來實現網路獲取，因為ImageLoader具有併發性，採用普通執行緒會產生大量的執行緒，影響效能，也不能採用AsyncTask，AsyncTask在3.0的低版本和高版本有差異。 2）獲取Bitmap，先從記憶體獲取，記憶體獲取不到再從磁碟獲取，最後磁碟獲取不到才需要網路獲取。 3）通過採用ImageView的setTag方法來解決圖片錯位的問題。
使用
ImageLoaderActivity：
public class ImageLoaderActivity extends AppCompatActivity
{
private GridView mGridView;
private List<String> mList = new ArrayList<>();
private GridAdapter mGridAdapter;
private Context mContext;
private ImageLoader mImageLoader;
public static final String[] PHOTOS = {
"http://f.hiphotos.baidu.com/image/pic/item/faf2b2119313b07e97f760d908d7912396dd8c9c.jpg",
"http://g.hiphotos.baidu.com/image/pic/item/4b90f603738da977c76ab6fab451f8198718e39e.jpg",
"http://e.hiphotos.baidu.com/image/pic/item/902397dda144ad343de8b756d4a20cf430ad858f.jpg",
"http://a.hiphotos.baidu.com/image/pic/item/a6efce1b9d16fdfa0fbc1ebfb68f8c5495ee7b8b.jpg",
"http://b.hiphotos.baidu.com/image/pic/item/a71ea8d3fd1f4134e61e0f90211f95cad1c85e36.jpg",
"http://c.hiphotos.baidu.com/image/pic/item/7dd98d1001e939011b9c86d07fec54e737d19645.jpg",
"http://f.hiphotos.baidu.com/image/pic/item/f11f3a292df5e0fecc3e83ef586034a85edf723d.jpg",
"http://cdn.duitang.com/uploads/item/201309/17/20130917111400_CNmTr.thumb.224_0.png",
"http://pica.nipic.com/2007-10-17/20071017111345564_2.jpg",
"http://pic4.nipic.com/20091101/3672704_160309066949_2.jpg",
"http://pic4.nipic.com/20091203/1295091_123813163959_2.jpg",
"http://pic31.nipic.com/20130624/8821914_104949466000_2.jpg",
"http://pic6.nipic.com/20100330/4592428_113348099353_2.jpg",
"http://pic9.nipic.com/20100917/5653289_174356436608_2.jpg",
"http://img10.3lian.com/sc6/show02/38/65/386515.jpg",
"http://pic1.nipic.com/2008-12-09/200812910493588_2.jpg",
"http://pic2.ooopic.com/11/79/98/31bOOOPICb1_1024.jpg" };
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_image_loader);
this.mContext = ImageLoaderActivity.this;
mImageLoader = ImageLoader.build(mContext);
mGridView = (GridView)this.findViewById(R.id.gridlist);
loadData();
mGridAdapter = new GridAdapter();
mGridView.setAdapter(mGridAdapter);
}
private void loadData()
{
for(int i = 0; i < 301; i++)
{
String photo = PHOTOS[getRandomNum(PHOTOS.length)];
mList.add(photo);
}
}
public static int getRandomNum(int max) {
Random random = new Random();
int result = random.nextInt(max);
return result;
}
private class GridAdapter extends BaseAdapter{
@Override
public int getCount()
{
return mList.size();
}
@Override
public Object getItem(int position)
{
return mList.get(position);
}
@Override
public long getItemId(int position)
{
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent)
{
ImageView imageView;
if(convertView == null){
imageView=new ImageView(mContext);
imageView.setBackgroundColor(0xffadadad);
imageView.setLayoutParams(new GridView.LayoutParams(300, 300));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
}else{
imageView = (ImageView) convertView;
}
mImageLoader.bindBitmap(mList.get(position),imageView,300,300);
return imageView;
}
}
}
複製程式碼使用的時候直接mImageLoader.bindBitmap(mList.get(position),imageView,300,300);方法即可。
佈局檔案：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
android:id="@+id/activity_image_loader"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.linwj.imageloader.ImageLoaderActivity">
<GridView
android:id="@+id/gridlist"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:columnWidth="90dp"
android:numColumns="auto_fit"
android:horizontalSpacing="10dp"
android:verticalSpacing="10dp"
android:stretchMode="columnWidth"
android:gravity="center"
/>
</RelativeLayout>
複製程式碼效果圖
上圖效果就是本文打造的圖片載入器的實戰成果，該圖片下載器採用了單一職責、開閉原則和介面分離原則等設計原則。
希望大家喜歡，如果讀者有什麼看法的可以給我留言。
參考文章： 《Android開發藝術探索》第十二章《Bitmap的載入和Cache》