Android中recyclerView底部添加透明渐变效果

 //gridLayoutManager这里设置的spanCount=2
 RecyclerView.LayoutManager manager = recyclerView.getLayoutManager();
 if (manager instanceof GridLayoutManager) {
 final GridLayoutManager gridManager = ((GridLayoutManager) manager);
 gridManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
  @Override
  public int getSpanSize(int position) {
  int type = getItemViewType(position);
  switch (type) {
  case TYPE_IMAGE:
  //占用1/2 表示2列
  Log.d("tag", "列数2");
  return 1;
  case TYPE_TEXT:
  //占用2/2 表示1列
  Log.d("tag", "列数1");
  return 2;
  default:
  Log.d("tag", "default列数2");
  return 2;
  }
  }
 });
 }

<shape xmlns:android="http://schemas.android.com/apk/res/android"
 android:shape="rectangle">
 <gradient
 android:angle="90"
 android:startColor="@color/color_FFFFFFFF"
 android:endColor="@color/color_00FFFFFF">
 </gradient>
</shape>

android:requiresFadingEdge="vertical"
android:fadingEdgeLength="40dp"

mRecycleView.setOnScrollListener(new RecyclerView.OnScrollListener() {
 @Override public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
 super.onScrolled(recyclerView, dx, dy);
 EdgeEffect mTopGlow = null;
 try {
  Field topGlow = mRecycleView.getClass().getDeclaredField("mTopGlow");
  if (topGlow != null) {
  topGlow.setAccessible(true);
  mTopGlow = (EdgeEffect) topGlow.get(mRecycleView);
  }
 } catch (Exception e) {
  e.printStackTrace();
 }

 if (mTopGlow != null) {
  //设置TOP顶部的矩形阴影大小（看注释和代码大概是这个作用）
  mTopGlow.setSize(0, 0);
  mTopGlow.finish();
 }
 }
 });

 public void makeTopGlowNoneNull() {
 final Class<?> clazz = RecyclerView.class;
 try {
 Method method = clazz.getDeclaredMethod("ensureTopGlow");
 method.setAccessible(true);
 method.invoke(mRecycleView);
 } catch (NoSuchMethodException e) {
 e.printStackTrace();
 } catch (IllegalAccessException e) {
 e.printStackTrace();
 } catch (InvocationTargetException e) {
 e.printStackTrace();
 }
 }

 /**
 * 利用itemDecoration的onDraw和onDrawOver回调时机，进行两个图层的合并
 *
 */
 mRecycleView.addItemDecoration(new RecyclerView.ItemDecoration() {
 @SuppressLint("NewApi") @Override public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
 super.onDraw(c, parent, state);
 layerId = c.saveLayer(0.0f, 0.0f, (float) parent.getWidth(), (float) parent.getHeight(), mPaint);
 }

 @Override public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
 super.onDrawOver(c, parent, state);
 if (linearGradient == null) {
  linearGradient = new LinearGradient(0f,parent.getHeight()-dpToPixel(54), 0f,
  parent.getHeight()-dpToPixel(15), new int[] {startColor,endColor },new float[]{0.2f,0.8f},
  Shader.TileMode.CLAMP);
 }
 mPaint.setXfermode(xfermode);
 mPaint.setShader(linearGradient);
 c.drawRect(0f,parent.getHeight()-dpToPixel(54),parent.getWidth(),parent.getHeight(),mPaint);
 mPaint.setXfermode(null);
 c.restoreToCount(layerId);
 /**
  * 第一次进去的时候发现画出来的东西很奇怪 暂未找到原因
  * 需要滑动之后才会正常显示，所以第一次进去的时候，手动调用一次刷新
  */

 if (recycleViewfirstComeInFlag == false) {
  recycleViewfirstComeInFlag = true;
  mRecycleView.postInvalidate();
 }
 }

 @Override public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
  RecyclerView.State state) {
 super.getItemOffsets(outRect, view, parent, state);
 }
 });
 }

 if (recycleViewfirstComeInFlag == false) {
   recycleViewfirstComeInFlag = true;
    mRecycleView.postInvalidate();
  }