RecyclerView現在可以說是很常用了吧？RecyclerView自然是很方便的控制元件，但用多了有時候對一些重複性程式碼也是感覺挺麻煩的，於是乎我就將一些重複性程式碼封裝了起來，從而使 RecyclerView 的使用更加的簡便
本篇部落格包含的內容有：
1. 通用的單佈局 RecyclerView.Adapter
2. 通用的多佈局 RecyclerView.Adapter
3. 通用的 RecyclerView.ItemDecoration
4. RecyclerView 的單擊和長按事件監聽
5. 帶頭部與底部View的 RecyclerView
6. SnapHelper 的使用
一、通用的 RecyclerView.Adapter
CommonRecyclerViewAdapter 是一個抽象類，利用泛型構造了一個通用的Adapter，並通過 MultiTypeSupport 介面來實現對多佈局的支援。 此外，有時候我們在重新整理資料時，改變的資料可能只是List集合中的單個資料，如果都採用 Adapter.notifyDataSetChanged() 來重新整理整個檢視，無疑是浪費資源的，此處採用了 DiffUtil 來對比前後兩個資料集，尋找出舊資料集與新資料集的最小變化量，從而對資料進行定向重新整理，可以只重新整理相應的Item，使得檢視的重新整理過程更為高效，且增添和刪除資料時都伴隨有相應的動畫效果
/**
* 作者：葉應是葉
* 時間：2017/12/21 21:50
* 說明：通用RecyclerView Adapter
*/
public abstract class CommonRecyclerViewAdapter<T> extends RecyclerView.Adapter<CommonRecyclerViewHolder> {
//省略一些程式碼
......
private DiffUtil.Callback callback = new DiffUtil.Callback() {
@Override
public int getOldListSize() {
return getItemCount();
}
@Override
public int getNewListSize() {
return newDataList.size();
}
@Override
public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
return CommonRecyclerViewAdapter.this.areItemsTheSame(oldItemPosition, newItemPosition);
}
@Override
public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
return CommonRecyclerViewAdapter.this.areContentsTheSame(oldItemPosition, newItemPosition);
}
@Nullable
@Override
public Object getChangePayload(int oldItemPosition, int newItemPosition) {
return CommonRecyclerViewAdapter.this.getChangePayload(oldItemPosition, newItemPosition);
}
};
public void setData(final List<T> dataList) {
new Thread(new Runnable() {
@Override
public void run() {
newDataList.clear();
newDataList = CommonRecyclerViewAdapter.this.clone(dataList);
DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(callback, true);
Message message = new Message();
message.what = DIFF_UTIL_UPDATE;
message.obj = diffResult;
handler.sendMessage(message);
}
}).start();
}
@Override
public int getItemViewType(int position) {
if (multiTypeSupport != null) {
return multiTypeSupport.getLayoutId(dataList.get(position), position);
}
return DEFAULT_ITEM_VIEW_TYPE;
}
@Override
public CommonRecyclerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (multiTypeSupport != null) {
layoutId = viewType;
}
return new CommonRecyclerViewHolder(layoutInflater.inflate(layoutId, parent, false));
}
@Override
public void onBindViewHolder(CommonRecyclerViewHolder holder, int position, List<Object> payloads) {
if (payloads.isEmpty()) {
onBindViewHolder(holder, position);
} else {
Bundle bundle = (Bundle) payloads.get(0);
partialBindData(holder, bundle);
}
}
@Override
public void onBindViewHolder(CommonRecyclerViewHolder holder, int position) {
entirelyBindData(holder, dataList.get(position));
if (clickListener != null) {
holder.setClickListener(clickListener);
}
if (longClickListener != null) {
holder.setLongClickListener(longClickListener);
}
}
//省略一些程式碼
......
private List<T> clone(List<T> dataList) {
List<T> tempDataList = new ArrayList<>(dataList.size());
for (T data : dataList) {
tempDataList.add(clone(data));
}
return tempDataList;
}
/**
* clone 指定物件，以此獲得物件副本
*
* @param data 要複製的物件
* @return 物件副本
*/
protected abstract T clone(T data);
/**
* 判斷資料列表重新整理前後指定索引的位置是否指向同一條資料
* 此處只對比兩者是否指向同一條資料，而不關心其資料內容是否有變化
*
* @param oldItemPosition 更新前的資料索引
* @param newItemPosition 更新後的資料索引
* @return 是否指向同一條資料
*/
protected abstract boolean areItemsTheSame(int oldItemPosition, int newItemPosition);
/**
* 此處來判斷指向同一條資料的前後兩個索引位置，其資料內容是否相同
* 只在 areItemsTheSame 返回 true 時才會呼叫本方法
*
* @param oldItemPosition 更新前的資料索引
* @param newItemPosition 更新後的資料索引
* @return 資料內容是否有變化
*/
protected abstract boolean areContentsTheSame(int oldItemPosition, int newItemPosition);
/**
* 獲取同條資料在重新整理前後是哪些資料內容發生了變化
* 只在 areContentsTheSame 返回 false 時才會呼叫本方法
*
* @param oldItemPosition 更新前的資料索引
* @param newItemPosition 更新後的資料索引
* @return 資料變化內容
*/
@NonNull
protected abstract Bundle getChangePayload(int oldItemPosition, int newItemPosition);
/**
* 對重新整理前後的資料進行定向更新，即只更新資料發生了變化的View
*
* @param holder Holder
* @param bundle getChangePayload 方法的返回值
*/
protected abstract void partialBindData(CommonRecyclerViewHolder holder, @NonNull Bundle bundle);
/**
* 對資料進行完全繫結
*
* @param holder Holder
* @param data Data
*/
protected abstract void entirelyBindData(CommonRecyclerViewHolder holder, T data);
}
複製程式碼此處還需要使用到一個通用的 RecyclerView.ViewHolder
/**
* 作者：葉應是葉
* 時間：2017/12/21 21:52
* 說明：通用RecyclerView ViewHolder
*/
public class CommonRecyclerViewHolder extends RecyclerView.ViewHolder {
public interface OnClickListener {
void onClick(int position);
}
public interface OnLongClickListener {
void onLongClick(int position);
}
private OnClickListener clickListener;
private OnLongClickListener longClickListener;
//用來存放View以減少findViewById的次數
private SparseArray<View> viewSparseArray;
CommonRecyclerViewHolder(View view) {
super(view);
viewSparseArray = new SparseArray<>();
view.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (clickListener != null) {
clickListener.onClick(getAdapterPosition());
}
}
});
view.setOnLongClickListener(new View.OnLongClickListener() {
@Override
public boolean onLongClick(View v) {
if (longClickListener != null) {
longClickListener.onLongClick(getAdapterPosition());
}
return true;
}
});
}
void setClickListener(OnClickListener clickListener) {
this.clickListener = clickListener;
}
void setLongClickListener(OnLongClickListener longClickListener) {
this.longClickListener = longClickListener;
}
/**
* 根據 ID 來獲取 View
*
* @param viewId viewID
* @param <T> 泛型
* @return 將結果強轉為 View 或 View 的子型別
*/
private <T extends View> T getView(@IdRes int viewId) {
// 先從快取中找，找到的話則直接返回
// 如果找不到則findViewById，再把結果存入快取中
View view = viewSparseArray.get(viewId);
if (view == null) {
view = itemView.findViewById(viewId);
if (view != null) {
viewSparseArray.put(viewId, view);
}
}
return (T) view;
}
public CommonRecyclerViewHolder setText(@IdRes int viewId, CharSequence text) {
TextView textView = getView(viewId);
if (textView != null) {
textView.setText(text);
}
return this;
}
//省略一些程式碼
......
}
複製程式碼二、通用的單佈局 RecyclerView.Adapter 使用示例
先來新建一個Model
/**
* 作者：葉應是葉
* 時間：2017/12/21 21:55
* 說明：
*/
public class New {
private int index;
private String title;
private String content;
public New(int index, String title, String content) {
this.index = index;
this.title = title;
this.content = content;
}
//省略一些程式碼
......
}
複製程式碼每個子項的佈局包含一個索引TextView、一個標題TextView、一個內容TextView
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#439af1"
android:orientation="vertical">
<TextView
android:id="@+id/tv_index"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:padding="6dp"
android:textSize="25sp"
android:textStyle="bold" />
<TextView
android:id="@+id/tv_title"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:padding="5dp"
android:textSize="28sp"
android:textStyle="bold" />
<TextView
android:id="@+id/tv_content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="start"
android:padding="10dp"
android:textSize="22sp" />
</LinearLayout>
複製程式碼之後就是繼承 CommonRecyclerViewAdapter ，泛型指定為 New ，在建構函式裡直接指定要使用的佈局為 R.layout.item_new，再實現幾個抽象方法即可。
/**
* 作者：葉應是葉
* 時間：2017/12/21 21:55
* 說明：單個佈局
*/
public class NewCommonAdapter extends CommonRecyclerViewAdapter<New> {
public NewCommonAdapter(Context context, List<New> dataList) {
super(context, dataList, R.layout.item_new);
}
@Override
protected New clone(New data) {
return new New(data.getIndex(), data.getTitle(), data.getContent());
}
@Override
protected boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
return dataList.get(oldItemPosition).getIndex() == newDataList.get(newItemPosition).getIndex();
}
@Override
protected boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
String title = dataList.get(oldItemPosition).getTitle();
String content = dataList.get(oldItemPosition).getContent();
String newTitle = newDataList.get(newItemPosition).getTitle();
String newContent = newDataList.get(newItemPosition).getContent();
return title.equals(newTitle) && content.equals(newContent);
}
@NonNull
@Override
protected Bundle getChangePayload(int oldItemPosition, int newItemPosition) {
Bundle bundle = new Bundle();
String title = dataList.get(oldItemPosition).getTitle();
String content = dataList.get(oldItemPosition).getContent();
String newTitle = newDataList.get(newItemPosition).getTitle();
String newContent = newDataList.get(newItemPosition).getContent();
if (!title.equals(newTitle)) {
bundle.putString("Title", newTitle);
}
if (!content.equals(newContent)) {
bundle.putString("Content", newContent);
}
return bundle;
}
@Override
protected void partialBindData(CommonRecyclerViewHolder holder, @NonNull Bundle bundle) {
for (String key : bundle.keySet()) {
switch (key) {
case "Title":
holder.setText(R.id.tv_title, bundle.getString(key));
break;
case "Content":
holder.setText(R.id.tv_content, bundle.getString(key));
break;
}
}
}
@Override
protected void entirelyBindData(CommonRecyclerViewHolder holder, New data) {
holder.setText(R.id.tv_title, data.getTitle())
.setText(R.id.tv_content, data.getContent());
}
}
複製程式碼這裡省略 Activity 中對 RecyclerView 的各種初始化操作，只展現最終效果，具體程式碼看最下方GitHub地址。 效果圖如下所示：
三、通用的多佈局 RecyclerView.Adapter 使用示例
在 CommonRecyclerViewAdapter 類當中，為了支援多佈局，通過 MultiTypeSupport 介面來返回相應的佈局檔案ID，這裡除了使用 單佈局 中使用的 R.layout.item_new 佈局檔案外，同時使用另外一個佈局檔案 R.layout.item_new_multi ，僅僅是背景色不同而已
想要讓子 Adapter 支援多佈局，只要實現 CommonRecyclerViewAdapter 的另外一個建構函式即可。這裡在索引為單數時使用 R.layout.item_new 佈局，雙數時使用 R.layout.item_new_multi 佈局
/**
* 作者：葉應是葉
* 時間：2017/12/21 21:56
* 說明：多佈局
*/
public class NewCommonMultiAdapter extends CommonRecyclerViewAdapter<New> {
public NewCommonMultiAdapter(Context context, List<New> dataList) {
super(context, dataList, new CommonRecyclerViewAdapter.MultiTypeSupport<New>() {
@Override
public int getLayoutId(New item, int position) {
return item.getIndex() % 2 == 0 ? R.layout.item_new_multi : R.layout.item_new;
}
});
}
//省略一些程式碼
......
@Override
protected void partialBindData(CommonRecyclerViewHolder holder, @NonNull Bundle bundle) {
if (bundle.size() > 0) {
int index = bundle.getInt("Index");
for (String key : bundle.keySet()) {
switch (key) {
case "Title":
if (index % 2 == 0) {
holder.setText(R.id.tv_multi_title, bundle.getString(key));
} else {
holder.setText(R.id.tv_title, bundle.getString(key));
}
break;
case "Content":
if (index % 2 == 0) {
holder.setText(R.id.tv_multi_content, bundle.getString(key));
} else {
holder.setText(R.id.tv_content, bundle.getString(key));
}
break;
}
}
}
}
@Override
protected void entirelyBindData(CommonRecyclerViewHolder holder, New data) {
if (data.getIndex() % 2 == 0) {
holder.setText(R.id.tv_multi_title, data.getTitle())
.setText(R.id.tv_multi_content, data.getContent())
.setText(R.id.tv_multi_index, String.valueOf(data.getIndex()));
} else {
holder.setText(R.id.tv_title, data.getTitle())
.setText(R.id.tv_content, data.getContent())
.setText(R.id.tv_index, String.valueOf(data.getIndex()));
}
}
}
複製程式碼實現的最終效果如下所示：
四、帶頭部與底部View的 RecyclerView
為了實現帶頭部與底部View的 RecyclerView ，需要自定義一個Adapter來包裹實際的Adapter，重寫 getItemViewType(int position) 方法，返回不同的值以區分頭部View與底部View，並向外開放新增和移除頭部底部View的方法
/**
* 作者：葉應是葉
* 時間：2017/12/21 21:53
* 說明：可新增頭部View與底部View的RecyclerView Adapter
*/
public class WrapRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private RecyclerView.Adapter<RecyclerView.ViewHolder> innerAdapter;
private SparseArray<View> headerViewArray;
private SparseArray<View> footerViewArray;
//頭部View型別開始位置,用於viewType
private static int BASE_VIEW_TYPE_HEADER = 1000;
//底部View型別開始位置,用於viewType
private static int BASE_VIEW_TYPE_FOOTER = 2000;
private RecyclerView.AdapterDataObserver dataObserver = new RecyclerView.AdapterDataObserver() {
@Override
public void onChanged() {
super.onChanged();
notifyDataSetChanged();
}
@Override
public void onItemRangeChanged(int positionStart, int itemCount) {
super.onItemRangeChanged(positionStart, itemCount);
notifyItemRangeChanged(positionStart + getHeaderViewCount(), itemCount);
}
@Override
public void onItemRangeInserted(int positionStart, int itemCount) {
super.onItemRangeInserted(positionStart, itemCount);
notifyItemRangeInserted(positionStart + getHeaderViewCount(), itemCount);
}
@Override
public void onItemRangeRemoved(int positionStart, int itemCount) {
super.onItemRangeRemoved(positionStart, itemCount);
notifyItemRangeRemoved(positionStart + getHeaderViewCount(), itemCount);
}
@Override
public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
super.onItemRangeMoved(fromPosition, toPosition, itemCount);
int headerViewsCountCount = getHeaderViewCount();
notifyItemRangeChanged(fromPosition + headerViewsCountCount, toPosition + headerViewsCountCount + itemCount);
}
};
public WrapRecyclerViewAdapter(RecyclerView.Adapter innerAdapter) {
headerViewArray = new SparseArray<>();
footerViewArray = new SparseArray<>();
setAdapter(innerAdapter);
}
private void setAdapter(RecyclerView.Adapter<RecyclerView.ViewHolder> adapter) {
innerAdapter = adapter;
innerAdapter.registerAdapterDataObserver(dataObserver);
}
@Override
public int getItemViewType(int position) {
if (isHeaderPosition(position)) {
return headerViewArray.keyAt(position);
}
if (isFooterPosition(position)) {
return footerViewArray.keyAt(position - headerViewArray.size() - getDataItemCount());
}
return innerAdapter.getItemViewType(position - headerViewArray.size());
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (isHeaderView(viewType)) {
return new ViewHolder(headerViewArray.get(viewType));
}
if (isFooterView(viewType)) {
return new ViewHolder(footerViewArray.get(viewType));
}
return innerAdapter.onCreateViewHolder(parent, viewType);
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
int headerViewsCountCount = getHeaderViewCount();
if (position >= headerViewsCountCount && position < headerViewsCountCount + innerAdapter.getItemCount()) {
innerAdapter.onBindViewHolder(holder, position - headerViewsCountCount);
}
}
@Override
public int getItemCount() {
return getHeaderViewCount() + getDataItemCount() + getFooterViewCount();
}
private int getDataItemCount() {
return innerAdapter == null ? 0 : innerAdapter.getItemCount();
}
public int getHeaderViewCount() {
return headerViewArray.size();
}
public int getFooterViewCount() {
return footerViewArray.size();
}
public RecyclerView.Adapter getInnerAdapter() {
return innerAdapter;
}
/**
* 判斷是否是頭部View
*
* @param viewType ViewType
* @return 是否是頭部View
*/
private boolean isHeaderView(int viewType) {
return headerViewArray.indexOfKey(viewType) > -1;
}
/**
* 判斷是否是底部View
*
* @param viewType ViewType
* @return 是否是底部View
*/
private boolean isFooterView(int viewType) {
return footerViewArray.indexOfKey(viewType) > -1;
}
/**
* 判斷是否是頭部View
*
* @param view View
* @return 是否是頭部View
*/
public boolean isHeaderView(View view) {
return headerViewArray.indexOfValue(view) > -1;
}
/**
* 判斷是否是底部View
*
* @param view View
* @return 是否是底部View
*/
public boolean isFooterView(View view) {
return footerViewArray.indexOfValue(view) > -1;
}
/**
* 根據索引判斷該位置的View是否是頭部View
*
* @param position 索引
* @return 是否是頭部View
*/
private boolean isHeaderPosition(int position) {
return position >= 0 && position < getHeaderViewCount();
}
/**
* 根據索引判斷該位置的View是否是底部View
*
* @param position 索引
* @return 是否是底部View
*/
private boolean isFooterPosition(int position) {
return position >= (getHeaderViewCount() + getDataItemCount())
&& position < (getHeaderViewCount() + getDataItemCount() + getFooterViewCount());
}
/**
* 新增頭部View
*
* @param view 頭部View
*/
public void addHeaderView(View view) {
if (headerViewArray.indexOfValue(view) < 0) {
headerViewArray.put(BASE_VIEW_TYPE_HEADER++, view);
notifyItemInserted(headerViewArray.size() - 1);
}
}
/**
* 新增底部View
*
* @param view 底部View
*/
public void addFooterView(View view) {
if (footerViewArray.indexOfValue(view) < 0) {
footerViewArray.put(BASE_VIEW_TYPE_FOOTER++, view);
notifyItemInserted(getHeaderViewCount() + getDataItemCount() + getFooterViewCount() - 1);
}
}
/**
* 移除頭部View
*
* @param view View
*/
public void removeHeaderView(View view) {
int index = headerViewArray.indexOfValue(view);
if (index > -1) {
headerViewArray.removeAt(index);
notifyItemRemoved(index);
}
}
/**
* 移除底部View
*
* @param view View
*/
public void removeFooterView(View view) {
int index = footerViewArray.indexOfValue(view);
if (index > -1) {
footerViewArray.removeAt(index);
notifyItemRemoved(getHeaderViewCount() + getDataItemCount() + index);
}
}
private class ViewHolder extends RecyclerView.ViewHolder {
ViewHolder(View itemView) {
super(itemView);
}
}
}
複製程式碼WrapRecyclerViewAdapter 的使用方法也很簡單，只要將實際的Adapter作為引數來構造 WrapRecyclerViewAdapter 物件，然後再傳給 RecyclerView 即可，之後就可以通過 addHeaderView 和 addFooterView 方法來新增頭部和底部View
RecyclerView rv_wrapDataList = (RecyclerView) findViewById(R.id.rv_wrapDataList);
NewCommonAdapter adapter = new NewCommonAdapter(this, newList);
WrapRecyclerViewAdapter wrapRecyclerViewAdapter = new WrapRecyclerViewAdapter(adapter);
rv_wrapDataList.setLayoutManager(new LinearLayoutManager(this));
rv_wrapDataList.setAdapter(wrapRecyclerViewAdapter);
複製程式碼使用效果如下所示：
五、RecyclerView 的單擊和長按事件監聽
RecyclerView 的單擊和長按事件一直是一個比較麻煩的地方，畢竟沒有官方提供的介面，不過此處 CommonRecyclerViewAdapter 也已經提供了相應的設定方法
NewCommonMultiAdapter newCommonMultiAdapter = new NewCommonMultiAdapter(this, newList);
newCommonMultiAdapter.setClickListener(new CommonRecyclerViewHolder.OnClickListener() {
@Override
public void onClick(int position) {
toast("單擊" + "\n" + newList.get(position).getTitle() + "\n" + newList.get(position).getContent());
}
});
newCommonMultiAdapter.setLongClickListener(new CommonRecyclerViewHolder.OnLongClickListener() {
@Override
public void onLongClick(int position) {
toast("長按" + "\n" + newList.get(position).getTitle() + "\n" + newList.get(position).getContent());
}
});
複製程式碼
六、通用的 RecyclerView.ItemDecoration
想要實現Item之間的分割線，需要繼承 RecyclerView.ItemDecoration 在相應的位置進行繪製，這裡提供一個通用的分隔線
/**
* 作者：葉應是葉
* 時間：2017/12/21 21:52
* 說明：通用分隔線
*/
public class CommonItemDecoration extends RecyclerView.ItemDecoration{
private int orientation = LinearLayoutManager.HORIZONTAL;
private Drawable drawable;
public CommonItemDecoration(Context context, int orientation) {
this.orientation = orientation;
int[] attrs = new int[]{android.R.attr.listDivider};
TypedArray typedArray = context.obtainStyledAttributes(attrs);
drawable = typedArray.getDrawable(0);
typedArray.recycle();
}
public CommonItemDecoration(Drawable drawable, int orientation) {
this.drawable = drawable;
this.orientation = orientation;
}
@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
if (orientation == LinearLayoutManager.HORIZONTAL) {
outRect.set(0, 0, drawable.getIntrinsicWidth(), 0);
} else if (orientation == LinearLayoutManager.VERTICAL) {
outRect.set(0, 0, 0, drawable.getIntrinsicHeight());
}
}
@Override
public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
super.onDraw(c, parent, state);
if (orientation == LinearLayoutManager.HORIZONTAL) {
drawVerticalDivider(c, parent);
} else if (orientation == LinearLayoutManager.VERTICAL) {
drawHorizontalDivider(c, parent);
}
}
private void drawVerticalDivider(Canvas c, RecyclerView parent) {
for (int i = 0; i < parent.getChildCount(); i++) {
View child = parent.getChildAt(i);
// RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
// //受 child layout_marginEnd 屬性的影響
// int left = child.getRight() + params.rightMargin;
//不受 child layout_marginEnd 屬性的影響，會直接繪製在 child 右側
int left = child.getRight();
int top = child.getTop();
int right = left + drawable.getIntrinsicWidth();
int bottom = child.getBottom();
drawable.setBounds(left, top, right, bottom);
drawable.draw(c);
}
}
private void drawHorizontalDivider(Canvas c, RecyclerView parent) {
for (int i = 0; i < parent.getChildCount(); i++) {
View child = parent.getChildAt(i);
int left = child.getLeft();
//不受 child layout_marginBottom 屬性的影響，會直接繪製在 child 底部
int top = child.getBottom();
int right = child.getRight();
int bottom = top + drawable.getIntrinsicHeight();
//會受 child layout_marginBottom 屬性的影響
//RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
//int top = child.getBottom() + params.bottomMargin;
drawable.setBounds(left, top, right, bottom);
drawable.draw(c);
}
}
}
複製程式碼在之前的幾張效果圖中，其實是已經為RecyclerView新增了一條白色分隔線的，
RecyclerView rv_commonMultiDataList = (RecyclerView) findViewById(R.id.rv_commonMultiDataList);
CommonItemDecoration commonItemDecoration = new CommonItemDecoration(ContextCompat.getDrawable(this, R.drawable.divider), LinearLayoutManager.VERTICAL);
rv_commonMultiDataList.addItemDecoration(commonItemDecoration);
複製程式碼這裡也可以傳入不同的 Drawable 物件，從而實現多種風格的分隔線
七、SnapHelper的使用
順帶在這裡對 SnapHelper 進行一個簡單的介紹，SnapHelper 是在 Android 24.2.0 的support 包中新新增的一個支援庫，是對RecyclerView的擴充。SnapHelper旨在支援RecyclerView的對齊方式，通過計算對齊RecyclerView中TargetView 的指定點或者容器中的任何畫素點，可以使RecyclerView實現類似於 ViewPager 的切換效果
SnapHelper是一個抽象類，官方提供了 LinearSnapHelper 和 PagerSnapHelper 兩個具體實現，這裡來實現類似於第一次使用App時顯示的引導頁的效果
/**
* 作者：葉應是葉
* 時間：2017/12/21 22:02
* 說明：
*/
public class SnapRecyclerViewActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_snap_recycler_view);
RecyclerView rv_snap = (RecyclerView) findViewById(R.id.rv_snap);
SnapAdapter snapAdapter = new SnapAdapter(this, getData());
rv_snap.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false));
// rv_snap.setLayoutManager(new LinearLayoutManager(this));
rv_snap.setAdapter(snapAdapter);
// LinearSnapHelper snapHelper = new LinearSnapHelper();
// snapHelper.attachToRecyclerView(rv_snap);
PagerSnapHelper pagerSnapHelper=new PagerSnapHelper();
pagerSnapHelper.attachToRecyclerView(rv_snap);
}
private List<Image> getData() {
List<Image> imageList = new ArrayList<>();
imageList.add(new Image(0, R.drawable.drawable_1));
imageList.add(new Image(1, R.drawable.drawable_0));
imageList.add(new Image(2, R.drawable.drawable_1));
imageList.add(new Image(3, R.drawable.drawable_0));
imageList.add(new Image(4, R.drawable.drawable_1));
imageList.add(new Image(5, R.drawable.drawable_0));
imageList.add(new Image(6, R.drawable.drawable_1));
imageList.add(new Image(7, R.drawable.drawable_0));
return imageList;
}
}
複製程式碼實現的效果如下所示：
