android Gallery實現非同步載入網路圖片 並只載入當前停止頁面圖

l_serein發表於2012-05-08
Android非同步
之前在網上找了很多都沒有這方面的資料，大概的效果是當Gallery滑動時不下載圖片，當Gallery滑動停止時載入當前頁面圖片，自己花了一點時間大概的實現了，如果各位有更好的意見歡迎說出來大家一起學習。
先上圖看看效果：
這圖是在載入圖片時顯示的預設圖片，當圖片載入完成則替換。

圖片載入完成效果圖

  1. import java.util.ArrayList;
  2. import java.util.HashMap;
  3. import java.util.List;
  4. import android.app.Activity;
  5. import android.graphics.Bitmap;
  6. import android.graphics.BitmapFactory;
  7. import android.os.AsyncTask;
  8. import android.os.Bundle;
  9. import android.os.Handler;
  10. import android.os.Message;
  11. import android.util.Log;
  12. import android.view.KeyEvent;
  13. import android.view.View;
  14. import android.widget.AdapterView;
  15. import android.widget.AdapterView.OnItemClickListener;
  16. import android.widget.AdapterView.OnItemSelectedListener;
  17. import android.widget.Gallery;
  18. public class MyActivity extends Activity implements OnItemClickListener{
  19. public static HashMap<String,Bitmap> imagesCache=new HashMap<String, Bitmap>(); //圖片快取
  20. private Gallery images_ga;
  21. public static ImageAdapter imageAdapter;
  22. private int num=0;
  23. List<String> urls = new ArrayList<String>(); //所有圖片地址List
  24. List<String> url = new ArrayList<String>(); //需要下載圖片的url地址

  26. @Override
  27. protected void onCreate(Bundle savedInstanceState) {

  29. super.onCreate(savedInstanceState);
  30. setContentView(R.layout.gallery_1);
  31. Files.mkdir(this);
  32. init();
  33. }
  34. private void init(){
  35. Bitmap image= BitmapFactory.decodeResource(getResources(),R.drawable.default_movie_post);
  36. imagesCache.put("background_non_load",image); //設定快取中預設的圖片
  37. images_ga = (Gallery) findViewById(R.id.gallery);
  38. urls.add("http://hiphotos.baidu.com/baidu/pic/item/f603918fa0ec08fabf7a641659ee3d6d55fbda0d.jpg");
  39. urls.add("http://hiphotos.baidu.com/baidu/pic/item/43a7d933c895d143d011bf9273f082025aaf071f.jpg");
  40. urls.add("http://hiphotos.baidu.com/baidu/pic/item/63d0f703918fa0ec2ebf584b269759ee3d6ddb7f.jpg");
  41. urls.add("http://hiphotos.baidu.com/baidu/pic/item/5ab5c9ea15ce36d31ed8387f3af33a87e850b1a5.jpg");
  42. urls.add("http://hiphotos.baidu.com/baidu/pic/item/8601a18b87d6277f6e46217628381f30e924fc2c.jpg");
  43. urls.add("http://hiphotos.baidu.com/baidu/pic/item/b48f8c54acf9964c3a29350e.jpg");
  44. urls.add("http://hiphotos.baidu.com/baidu/pic/item/bd3eb13533fa828b48da6aabfd1f4134960a5af9.jpg");
  45. urls.add("http://hiphotos.baidu.com/baidu/pic/item/29381f30e924b899da3ce5706e061d950a7bf672.jpg");
  46. urls.add("http://hiphotos.baidu.com/baidu/pic/item/bd3eb13533fa828b48da6aabfd1f4134960a5af9.jpg");
  47. urls.add("http://hiphotos.baidu.com/baidu/pic/item/4bed2e738bd4b31cd73d63fd87d6277f9e2ff877.jpg");
  48. urls.add("http://hiphotos.baidu.com/baidu/pic/item/caef76094b36acaf92b619b87cd98d1001e99c24.jpg");
  49. urls.add("http://hiphotos.baidu.com/baidu/pic/item/8435e5dde71190efd6154d95ce1b9d16fcfa608a.jpg");
  50. urls.add("http://hiphotos.baidu.com/baidu/pic/item/b3de9c824ba1d4cd6d81190f.jpg");
  51. urls.add("http://hiphotos.baidu.com/baidu/pic/item/e0fe9925cc2c683834a80f11.jpg");
  52. urls.add("http://hiphotos.baidu.com/baidu/pic/item/0bd162d9f2d3572c65911a988a13632762d0c307.jpg");
  53. urls.add("http://hiphotos.baidu.com/baidu/pic/item/ac6eddc451da81cb2ac1708a5266d01609243155.jpg");

  55. urls.add("http://hiphotos.baidu.com/baidu/pic/item/1bd5ad6e8416d98080cb4a48.jpg");
  56. urls.add("http://hiphotos.baidu.com/baidu/pic/item/3c6d55fbb2fb43169d0508ca20a4462309f7d36c.jpg");
  57. urls.add("http://hiphotos.baidu.com/baidu/pic/item/faedab64034f78f0daf3664a79310a55b2191c8a.jpg");
  58. urls.add("http://hiphotos.baidu.com/baidu/pic/item/2fdda3cc7cd98d10b05af088213fb80e7aec90f9.jpg");
  59. urls.add("http://hiphotos.baidu.com/baidu/pic/item/b8014a90f603738d9536f39bb31bb051f819ec0f.jpg");
  60. urls.add("http://hiphotos.baidu.com/baidu/pic/item/2fdda3cc7cd98d10b05af088213fb80e7aec90f9.jpg");
  61. imageAdapter = new ImageAdapter(urls, this);
  62. images_ga.setAdapter(imageAdapter);
  63. images_ga.setOnItemClickListener(this);
  64. images_ga.setOnItemSelectedListener(new OnItemSelectedListener() {
  65. @Override
  66. public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
  67. num=arg2;
  68. Log.i("mahua", "ItemSelected=="+arg2);
  69. GalleryWhetherStop();
  70. }
  71. @Override
  72. public void onNothingSelected(AdapterView<?> arg0) {
  73. // TODO Auto-generated method stub

  75. }
  76. });
  77. }


  80. @Override
  81. public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
  82. Log.i("GOLF", "第"+arg2+"個被點選了");
  83. }

  85. /**
  86. * 判斷Gallery滾動是否停止,如果停止則載入當前頁面的圖片
  87. */
  88. private void GalleryWhetherStop() {
  89. Runnable runnable = new Runnable() {
  90. public void run() {
  91. try {
  92. int index =0;
  93. index = num;
  94. Thread.sleep(1000);
  95. if (index == num) {
  96. url.add(urls.get(num));
  97. if(num!=0 && urls.get(num-1)!=null) {
  98. url.add(urls.get(num-1));
  99. }
  100. if(num!=urls.size()-1 && urls.get(num+1)!=null) {
  101. url.add(urls.get(num+1));
  102. }
  103. Message m = new Message();
  104. m.what = 1;
  105. mHandler.sendMessage(m);
  106. }
  107. } catch (Exception e) {
  108. e.printStackTrace();
  109. }
  110. }
  111. };
  112. new Thread(runnable).start();
  113. }


  116. // 載入圖片的非同步任務
  117. class LoadImageTask extends AsyncTask<String, Void, Bitmap> {
  118. @Override 
  119. protected void onCancelled() { 
  120. // TODO Auto-generated method stub 
  121. super.onCancelled(); 
  122. } 
  123. @Override 
  124. protected void onPostExecute(Bitmap result) { 
  125. // TODO Auto-generated method stub 
  126. super.onPostExecute(result); 
  127. } 

  129. @Override
  130. protected Bitmap doInBackground(String... params) {
  131. Bitmap bitmap = null;
  132. try {
  133. String url = params[0];
  134. boolean isExists = Files.compare(url); //這裡是自己寫的工具類，判斷本地快取是否已經下載過圖片
  135. if (isExists == false) {//如果不存在就去下載圖片
  136. Net net = new Net();
  137. byte[] data = net.downloadResource(MyActivity.this, url);
  138. bitmap = BitmapFactory
  139. .decodeByteArray(data, 0, data.length);
  140. imagesCache.put(url, bitmap); // 把下載好的圖片儲存到快取中
  141. Files.saveImage(url, data);
  142. } else {//如果存在直接讀取快取圖片
  143. byte[] data = Files.readImage(url);
  144. bitmap = BitmapFactory
  145. .decodeByteArray(data, 0, data.length);
  146. imagesCache.put(url, bitmap); // 把下載好的圖片儲存到快取中
  147. }
  148. Message m = new Message();//圖片載入完成通知重新載入
  149. m.what = 0;
  150. mHandler.sendMessage(m);
  151. } catch (Exception e) {
  152. e.printStackTrace();
  153. }
  154. return bitmap;
  155. }

  157. }


  160. private Handler mHandler = new Handler() {
  161. public void handleMessage(Message msg) {
  162. try {
  163. switch (msg.what) {
  164. case 0: {
  165. imageAdapter.notifyDataSetChanged();
  166. break;
  167. }
  168. case 1: {
  169. for(int i=0; i<url.size(); i++) {
  170. LoadImageTask task = new LoadImageTask();//非同步載入圖片
  171. task.execute(url.get(i));
  172. Log.i("mahua", url.get(i));
  173. }
  174. url.clear();
  175. }
  176. }
  177. super.handleMessage(msg);
  178. } catch (Exception e) {
  179. e.printStackTrace();
  180. }
  181. }
  182. };
  183. @Override
  184. public boolean onKeyDown(int keyCode, KeyEvent event) {
  185. if(keyCode==KeyEvent.KEYCODE_BACK){
  186. System.exit(0);
  187. }
  188. return super.onKeyDown(keyCode, event);
  189. }
  190. }
複製程式碼
  1. import java.util.List;
  2. import android.content.Context;
  3. import android.content.res.AssetManager;
  4. import android.content.res.TypedArray;
  5. import android.graphics.Bitmap;
  6. import android.view.View;
  7. import android.view.ViewGroup;
  8. import android.widget.BaseAdapter;
  9. import android.widget.Gallery;
  10. import android.widget.ImageView;

  12. public class ImageAdapter extends BaseAdapter {
  13. public static final BaseAdapter Adapter = null;
  14. private List<String> imageUrls; // 圖片地址list
  15. private Context context;
  16. int mGalleryItemBackground;

  18. public ImageAdapter(List<String> imageUrls, Context context) {
  19. this.imageUrls = imageUrls;
  20. this.context = context;
  21. // /*
  22. // * 使用在res/values/attrs.xml中的<declare-styleable>定義 的Gallery屬性.
  23. // */
  24. TypedArray a = context.obtainStyledAttributes(R.styleable.Gallery1);
  25. /* 取得Gallery屬性的Index id */
  26. mGalleryItemBackground = a.getResourceId(
  27. R.styleable.Gallery1_android_galleryItemBackground, 0);
  28. /* 讓物件的styleable屬效能夠反覆使用 */
  29. a.recycle();
  30. }
  31. public int getCount() {
  32. return imageUrls.size();
  33. }
  34. public Object getItem(int position) {
  35. return imageUrls.get(position);
  36. }
  37. public long getItemId(int position) {
  38. return position;
  39. }
  40. public View getView(int position, View convertView, ViewGroup parent) {
  41. Bitmap image;
  42. ImageView view = new ImageView(context);
  43. image = MyActivity.imagesCache.get(imageUrls.get(position));
  44. // 從快取中讀取圖片
  45. if (image == null) {
  46. image = MyActivity.imagesCache.get("background_non_load");
  47. }
  48. // 設定所有圖片的資源地址
  49. view.setImageBitmap(image);
  50. view.setScaleType(ImageView.ScaleType.FIT_XY);
  51. view.setLayoutParams(new Gallery.LayoutParams(240, 320));
  52. view.setBackgroundResource(mGalleryItemBackground);
  53. /* 設定Gallery背景圖 */
  54. return view;
  55. }
  56. }
複製程式碼

attrs.xml

  1. <?xml version="1.0" encoding="utf-8"?>
  2. <resources>
  3. <declare-styleable name="TogglePrefAttrs">
  4. <attr name="android:preferenceLayoutChild" />
  5. </declare-styleable>

  7. <!-- These are the attributes that we want to retrieve from the theme
  8. in view/Gallery1.java -->
  9. <declare-styleable name="Gallery1">
  10. <attr name="android:galleryItemBackground" />
  11. </declare-styleable>

  13. <declare-styleable name="LabelView">
  14. <attr name="text" format="string" />
  15. <attr name="textColor" format="color" />
  16. <attr name="textSize" format="dimension" />
  17. </declare-styleable>
  18. </resources>
複製程式碼

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