public class ItemEmoje { //坐標 public int x; public int y; // 橫向偏移 public int offsetX; //縱向偏移 public int offsetY; //縮放 public float scale; //圖片資源 public Bitmap bitmap;}

public class RainView extends View { private Paint paint; //圖片處理 private Matrix matrix; private Random random; //判斷是否運行的，默認沒有 private boolean isRun; //表情包集合 private List<ItemEmoje> bitmapList; //表情圖片 private int imgResId = R.mipmap.dog; public RainView(Context context) { this(context, null); } public RainView(Context context, @Nullable AttributeSet attrs) { this(context, attrs, 0); } public RainView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); init(); } private void init() { paint = new Paint(); paint.setAntiAlias(true); paint.setFilterBitmap(true); paint.setDither(true); matrix = new Matrix(); random = new Random(); bitmapList = new ArrayList<>(); }}

private void initData() { for (int i = 0; i < 20; i++) { ItemEmoje itemEmoje = new ItemEmoje(); itemEmoje.bitmap = BitmapFactory.decodeResource(getResources(), imgResId); //起始橫坐標在[100,getWidth()-100) 之間 itemEmoje.x = random.nextInt(getWidth() - 200) + 100; //起始縱坐標在(-getHeight(),0] 之間，即一開始位于屏幕上方以外 itemEmoje.y = -random.nextInt(getHeight()); //橫向偏移[-2,2) ，即左右搖擺區間 itemEmoje.offsetX = random.nextInt(4) - 2; //縱向固定下落12 itemEmoje.offsetY = 12; //縮放比例[0.8,1.2) 之間 itemEmoje.scale = (float) (random.nextInt(40) + 80) / 100f; bitmapList.add(itemEmoje); }}

@Overrideprotected void onDraw(Canvas canvas) { super.onDraw(canvas); if (isRun) { //用于判斷表情下落結束，結束即不再進行重繪 boolean isInScreen = false; for (int i = 0; i < bitmapList.size(); i++) {  matrix.reset();  //縮放  matrix.setScale(bitmapList.get(i).scale, bitmapList.get(i).scale);  //下落過程坐標  bitmapList.get(i).x = bitmapList.get(i).x + bitmapList.get(i).offsetX;  bitmapList.get(i).y = bitmapList.get(i).y + bitmapList.get(i).offsetY;  if (bitmapList.get(i).y <= getHeight()) {//當表情仍在視圖內，則繼續重繪  isInScreen = true;  }  //位移  matrix.postTranslate(bitmapList.get(i).x, bitmapList.get(i).y);  canvas.drawBitmap(bitmapList.get(i).bitmap, matrix, paint); } if (isInScreen) {  postInvalidate(); }else {  release(); } }}/** *釋放資源 */private void release(){ if(bitmapList != null && bitmapList.size()>0){ for(ItemEmoje itemEmoje : bitmapList){  if(!itemEmoje.bitmap.isRecycled()){  itemEmoje.bitmap.recycle();  } } bitmapList.clear(); }}

public void start(boolean isRun) { this.isRun = isRun; initData(); postInvalidate();}

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <com.rain.RainView android:id="@+id/testView" android:layout_width="match_parent" android:layout_height="match_parent" /> <Button android:id="@+id/btn_dog" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:text="真?狗頭雨?落！" /> <Button android:id="@+id/btn_cake" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:layout_marginLeft="10dp" android:layout_toRightOf="@+id/btn_dog" android:text="蛋糕雨" /></RelativeLayout>

btnCake.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { //蛋糕圖片 rainView.setImgResId(R.mipmap.cake); rainView.start(true); }});btnDog.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { //狗頭圖片 rainView.setImgResId(R.mipmap.dog); rainView.start(true); }});