RecyclerView使用詳解（三）
阿新 • • 發佈：2018-12-19
在上一篇（RecyclerView使用詳解（二））文章中介紹了RecyclerView的多Item佈局實現，接下來要來講講RecyclerView的Cursor實現，相較於之前的實現，Cursor有更多的使用場景，也更加的常用，特別是配合LoaderManager和CursorLoader進行資料的快取及載入顯示，基於此我們來重點看看RecyclerView的CursorAdapter具體要怎麼實現。
一、CursorAdapter實現(配合LoaderManager和CursorLoader)
如果之前你用過ListView實現過此功能(CursorAdapter)，那麼你一定對下面這兩個方法並不陌生
@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {
return null;
}
@Override
public void bindView(View view, Context context, Cursor cursor) {
}其中newView方法是用來建立Item佈局的，bindView 方法是用來綁定當前View資料的，就相當於之前的getView方法拆成了兩個方法實現。
如果你用RecyclerView，你會發現CursorAdapter
void init(Context context, Cursor c, int flags) { boolean cursorPresent = c != null; mCursor = c; mDataValid = cursorPresent; mContext = context; mRowIDColumn = cursorPresent ? c.getColumnIndexOrThrow("_id") : -1; if ((flags & FLAG_REGISTER_CONTENT_OBSERVER) == FLAG_REGISTER_CONTENT_OBSERVER) { mChangeObserver = new ChangeObserver(); mDataSetObserver = new MyDataSetObserver(); } else { mChangeObserver = null; mDataSetObserver = null; } if (cursorPresent) { if (mChangeObserver != null) c.registerContentObserver(mChangeObserver); if (mDataSetObserver != null) c.registerDataSetObserver(mDataSetObserver); } setHasStableIds(true);//這個地方要注意一下，需要將表關聯ID設定為true } //************// public Cursor swapCursor(Cursor newCursor) { if (newCursor == mCursor) { return null; } Cursor oldCursor = mCursor; if (oldCursor != null) { if (mChangeObserver != null) oldCursor.unregisterContentObserver(mChangeObserver); if (mDataSetObserver != null) oldCursor.unregisterDataSetObserver(mDataSetObserver); } mCursor = newCursor; if (newCursor != null) { if (mChangeObserver != null) newCursor.registerContentObserver(mChangeObserver); if (mDataSetObserver != null) newCursor.registerDataSetObserver(mDataSetObserver); mRowIDColumn = newCursor.getColumnIndexOrThrow("_id"); mDataValid = true; // notify the observers about the new cursor notifyDataSetChanged(); } else { mRowIDColumn = -1; mDataValid = false; // notify the observers about the lack of a data set //There is no notifyDataSetInvalidated() method in RecyclerView.Adapter notifyDataSetChanged();//注意此處 } return oldCursor; } //************// private class MyDataSetObserver extends DataSetObserver { @Override public void onChanged() { mDataValid = true; notifyDataSetChanged(); } @Override public void onInvalidated() { mDataValid = false; //There is no notifyDataSetInvalidated() method in RecyclerView.Adapter notifyDataSetChanged();//注意此處 } }
二、Item的動畫實現
RecyclerView本身就已經實現了ITEM的動畫，只需要呼叫以下幾個函式來增刪Item即可出現預設動畫。
notifyItemChanged(int)
notifyItemInserted(int)
notifyItemRemoved(int)
notifyItemRangeChanged(int, int)
notifyItemRangeInserted(int, int)
notifyItemRangeRemoved(int, int)怎麼樣，是不是很輕鬆，如果你不滿足系統預設動畫，那麼你可以自定義實現RecyclerView.ItemAnimator的介面方法，實現程式碼可以參考DefaultItemAnimator.當然，如果你不想自己實現，那麼也沒關係，這裡有人已經寫了開源庫，你可以去看看recyclerview-animators,這裡給出預設動畫實現方式程式碼AnimFragment
三、巢狀RecycleView
一般是不推薦使用巢狀RecycleView的，和ListView是類似的，遇到這種需要巢狀的View一般都是想別的辦法來規避，比如動態AddView，或者通過RecycleView的MultipleItemAdapter來實現，通過設定不同的ItemType佈局不同的View，但是有時候會閒麻煩，想直接就用巢狀的方式來做，那麼和ListView實現方式不同的是，ListView的實現一般都是繼承ListView然後複寫onMeasure方法，如下所示：
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int expandSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 2, MeasureSpec.AT_MOST);
super.onMeasure(widthMeasureSpec, expandSpec);
}但是RecycleView的實現方式不再是繼承RecycleView來做，而是通過修改LayoutManager的方式，即通過繼承LinearLayoutManager GridLayoutManager StaggeredGridLayoutManager來修改子控制元件的測量，下面給出主要程式碼：
private int[] mMeasuredDimension = new int[2];
@Override
public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state,
int widthSpec, int heightSpec) {
final int widthMode = View.MeasureSpec.getMode(widthSpec);
final int heightMode = View.MeasureSpec.getMode(heightSpec);
final int widthSize = View.MeasureSpec.getSize(widthSpec);
final int heightSize = View.MeasureSpec.getSize(heightSpec);
Log.i(TAG, "onMeasure called. \nwidthMode " + widthMode
+ " \nheightMode " + heightSpec
+ " \nwidthSize " + widthSize
+ " \nheightSize " + heightSize
+ " \ngetItemCount() " + getItemCount());
int width = 0;
int height = 0;
for (int i = 0; i < getItemCount(); i++) {
measureScrapChild(recycler, i,
View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
mMeasuredDimension);
if (getOrientation() == HORIZONTAL) {
width = width + mMeasuredDimension[0];
if (i == 0) {
height = mMeasuredDimension[1];
}
} else {
height = height + mMeasuredDimension[1];
if (i == 0) {
width = mMeasuredDimension[0];
}
}
}
switch (widthMode) {
case View.MeasureSpec.EXACTLY:
width = widthSize;
case View.MeasureSpec.AT_MOST:
case View.MeasureSpec.UNSPECIFIED:
}
switch (heightMode) {
case View.MeasureSpec.EXACTLY:
height = heightSize;
case View.MeasureSpec.AT_MOST:
case View.MeasureSpec.UNSPECIFIED:
}
setMeasuredDimension(width, height);
}
private void measureScrapChild(RecyclerView.Recycler recycler, int position, int widthSpec,
int heightSpec, int[] measuredDimension) {
try {
View view = recycler.getViewForPosition(0);//fix 動態新增時報IndexOutOfBoundsException
if (view != null) {
RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) view.getLayoutParams();
int childWidthSpec = ViewGroup.getChildMeasureSpec(widthSpec,
getPaddingLeft() + getPaddingRight(), p.width);
int childHeightSpec = ViewGroup.getChildMeasureSpec(heightSpec,
getPaddingTop() + getPaddingBottom(), p.height);
view.measure(childWidthSpec, childHeightSpec);
measuredDimension[0] = view.getMeasuredWidth() + p.leftMargin + p.rightMargin;
measuredDimension[1] = view.getMeasuredHeight() + p.bottomMargin + p.topMargin;
recycler.recycleView(view);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
}
} private int[] mMeasuredDimension = new int[2];
@Override
public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state, int widthSpec, int heightSpec) {
final int widthMode = View.MeasureSpec.getMode(widthSpec);
final int heightMode = View.MeasureSpec.getMode(heightSpec);
final int widthSize = View.MeasureSpec.getSize(widthSpec);
final int heightSize = View.MeasureSpec.getSize(heightSpec);
int width = 0;
int height = 0;
int count = getItemCount();
int span = getSpanCount();
for (int i = 0; i < count; i++) {
measureScrapChild(recycler, i,
View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
View.MeasureSpec.makeMeasureSpec(i, View.MeasureSpec.UNSPECIFIED),
mMeasuredDimension);
if (getOrientation() == HORIZONTAL) {
if (i % span == 0) {
width = width + mMeasuredDimension[0];
}
if (i == 0) {
height = mMeasuredDimension[1];
}
} else {
if (i % span == 0) {
height = height + mMeasuredDimension[1];
}
if (i == 0) {
width = mMeasuredDimension[0];
}
}
}
switch (widthMode) {
case View.MeasureSpec.EXACTLY:
width = widthSize;
case View.MeasureSpec.AT_MOST:
case View.MeasureSpec.UNSPECIFIED:
}
switch (heightMode) {
case View.MeasureSpec.EXACTLY:
height = heightSize;
case View.MeasureSpec.AT_MOST:
case View.MeasureSpec.UNSPECIFIED:
}
setMeasuredDimension(width, height);
}
private void measureScrapChild(RecyclerView.Recycler recycler, int position, int widthSpec,
int heightSpec, int[] measuredDimension) {
if (position < getItemCount()) {
try {
View view = recycler.getViewForPosition(0);//fix 動態新增時報IndexOutOfBoundsException
if (view != null) {
RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) view.getLayoutParams();
int childWidthSpec = ViewGroup.getChildMeasureSpec(widthSpec,
getPaddingLeft() + getPaddingRight(), p.width);
int childHeightSpec = ViewGroup.getChildMeasureSpec(heightSpec,
getPaddingTop() + getPaddingBottom(), p.height);
view.measure(childWidthSpec, childHeightSpec);
measuredDimension[0] = view.getMeasuredWidth() + p.leftMargin + p.rightMargin;
measuredDimension[1] = view.getMeasuredHeight() + p.bottomMargin + p.topMargin;
recycler.recycleView(view);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}四、效果圖如下：
Item預設動畫效果
巢狀ScrollView效果
最後給出程式碼下載地址–>Demo Code