public interface Callback {

// SurfaceView 创建时调用(SurfaceView的窗口可见时)
 public void surfaceCreated(SurfaceHolder holder);

// SurfaceView 改变时调用 
 public void surfaceChanged(SurfaceHolder holder, int format, int width,
 int height);

// SurfaceView 销毁时调用(SurfaceView的窗口不可见时)
 public void surfaceDestroyed(SurfaceHolder holder);

 }

public class DynamicWeatherView extends SurfaceView implements SurfaceHolder.Callback{

 public DynamicWeatherView(Context context) {
 this(context, null);
 }

 public DynamicWeatherView(Context context, AttributeSet attrs) {
 this(context, attrs, 0);
 }

 public DynamicWeatherView(Context context, AttributeSet attrs, int defStyleAttr) {
 super(context, attrs, defStyleAttr);
 }

 // SurfaceView 创建时调用(可见)
 @Override
 public void surfaceCreated(SurfaceHolder holder) {

 }

 // SurfaceView 销毁时调用(不可见)
 @Override
 public void surfaceDestroyed(SurfaceHolder holder) {

 }

 @Override
 public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

 }

}

private SurfaceHolder mHolder;

mHolder = getHolder();
mHolder.addCallback(this);
mHolder.setFormat(PixelFormat.TRANSPARENT);

private class DrawThread extends Thread {

 // 用来停止线程的标记
 private boolean isRunning = false;

 public void setRunning(boolean running) {
 isRunning = running;
 }

 @Override
 public void run() {
 Canvas canvas;
 // 无限循环绘制
 while (isRunning) {
 if (mType != null && mViewWidth != 0 && mViewHeight != 0) {
 canvas = mHolder.lockCanvas();
 if (canvas != null) {
 mType.onDraw(canvas);
 if (isRunning) {
 mHolder.unlockCanvasAndPost(canvas);
 } else {
 // 停止线程
 break;
 }
 SystemClock.sleep(1);
 }
 }
 }
 }
}

// 锁定画布并获得 canvas
canvas = mHolder.lockCanvas();
// 在 canvas 上进行绘制
mType.onDraw(canvas);
// 解除锁定并提交更改
mHolder.unlockCanvasAndPost(canvas);

public interface WeatherType {
 void onDraw(Canvas canvas);

 void onSizeChanged(Context context, int w, int h);
}

public class RainTypeImpl extends BaseType {

 // 背景
 private Drawable mBackground;
 // 雨滴集合
 private ArrayList<RainHolder> mRains;
 // 画笔
 private Paint mPaint;

 public RainTypeImpl(Context context, DynamicWeatherView dynamicWeatherView) {
 super(context, dynamicWeatherView);
 init();
 }

 private void init() {
 mPaint = new Paint();
 mPaint.setAntiAlias(true);
 mPaint.setColor(Color.WHITE);
 // 这里雨滴的宽度统一为3
 mPaint.setStrokeWidth(3);
 mRains = new ArrayList<>();
 }

 @Override
 public void generate() {
 mBackground = getContext().getResources().getDrawable(R.drawable.rain_sky_night);
 mBackground.setBounds(0, 0, getWidth(), getHeight());
 for (int i = 0; i < 60; i++) {
 RainHolder rain = new RainHolder(
 getRandom(1, getWidth()),
 getRandom(1, getHeight()),
 getRandom(dp2px(9), dp2px(15)),
 getRandom(dp2px(5), dp2px(9)),
 getRandom(20, 100)
 );
 mRains.add(rain);
 }
 }

 private RainHolder r;

 @Override
 public void onDraw(Canvas canvas) {
 clearCanvas(canvas);
 // 画背景
 mBackground.draw(canvas);
 // 画出集合中的雨点
 for (int i = 0; i < mRains.size(); i++) {
 r = mRains.get(i);
 mPaint.setAlpha(r.a);
 canvas.drawLine(r.x, r.y, r.x, r.y + r.l, mPaint);
 }
 // 将集合中的点按自己的速度偏移
 for (int i = 0; i < mRains.size(); i++) {
 r = mRains.get(i);
 r.y += r.s;
 if (r.y > getHeight()) {
 r.y = -r.l;
 }
 }
 }

 private class RainHolder {
 /**
 * 雨点 x 轴坐标
 */
 int x;
 /**
 * 雨点 y 轴坐标
 */
 int y;
 /**
 * 雨点长度
 */
 int l;
 /**
 * 雨点移动速度
 */
 int s;
 /**
 * 雨点透明度
 */
 int a;

 public RainHolder(int x, int y, int l, int s, int a) {
 this.x = x;
 this.y = y;
 this.l = l;
 this.s = s;
 this.a = a;
 }

 }

}

public class MainActivity extends Activity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 DynamicWeatherView mDynamicWeatherView = (DynamicWeatherView) findViewById(R.id.dynamic_weather_view);
 mDynamicWeatherView.setType(new RainTypeImpl(this, mDynamicWeatherView));
 }
}