Android双重SurfaceView实现弹幕效果

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical"
  tools:context=".DanmuActivity">

  <SurfaceView
    android:id="@ id/sv_text"
    android:layout_width="match_parent"
    android:layout_height="400dp"/>

  <SurfaceView
    android:id="@ id/sv_media"
    android:layout_width="match_parent"
    android:layout_height="400dp"/>
    />


  <EditText
    android:id="@ id/et_text"
    android:layout_width="300dp"
    android:layout_height="wrap_content"
    android:layout_marginTop="450dp"/>

  <Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="发送"
    android:layout_marginTop="500dp"
    android:onClick="Gogo"/>
</FrameLayout>

public class Danmu {

  String text;//弹幕内容
  int x;//x轴
  int y;//y轴

  public Danmu(String text){
    this.text = text;
    //将y设置为随机,弹幕出现的位置也为随机
    this.y = (int) (Math.random()*400);
    this.x = 0;
  }
}

//视频播放
private MediaPlayer mediaPlayer;
//弹幕Surface与视频Surface
private SurfaceView sv_text, sv_media;
//两个Surface对应的两个holder
private SurfaceHolder text_holder, media_holder;
EditText editText;//字幕输入框
List<Danmu> list = new ArrayList<>();//存放

private void initPlayer() throws IOException {
 //先判断是否创建过,没创建就创建出来
    if (mediaPlayer == null) {
      mediaPlayer = new MediaPlayer();
    }
    mediaPlayer.reset();//使其恢复空闲状态
    //播放的资源
    mediaPlayer.setDataSource("http://clips.vorwaerts-gmbh.de/big_buck_bunny.mp4");
    mediaPlayer.prepare();//准备
    mediaPlayer.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
      @Override
      public void onPrepared(MediaPlayer mp) {//准备完毕了
        mediaPlayer.start();//播放
      }
    });
  }

private void initView() {

    sv_text = findViewById(R.id.sv_text);
    text_holder = sv_text.getHolder();
    text_holder.addCallback(this);

    sv_media = findViewById(R.id.sv_media);
    media_holder = sv_media.getHolder();
    media_holder.addCallback(this);

    editText = findViewById(R.id.et_text);

    //设置透明,将播放弹幕的Surface放到第一位并设置为背景透明
    sv_text.setZOrderOnTop(true);
    text_holder.setFormat(PixelFormat.TRANSPARENT);
  }

@Override
  public void surfaceCreated(SurfaceHolder holder) {
  //判断当前holder是否是media的那个
    if (holder == media_holder) {
    //设置要显示的Surfaceholder
      mediaPlayer.setDisplay(media_holder);
        //判断当前holder是否是字幕的那个
    } else if (holder == text_holder) {
    //创建线程执行耗时操作
      new Thread() {
        @Override
        public void run() {
          super.run();
          //死循环用来一直更新弹幕的位置
          while (true) {
            try {
              Thread.sleep(500);
            } catch (InterruptedException e) {
              e.printStackTrace();
            }
  Paint paint = new Paint();//创建画笔
 paint.setStrokeWidth(5);//画笔粗细
 paint.setColor(Color.GREEN);//画笔颜色
  paint.setTextSize(30);//设置文字大小
 //创建画板
   Canvas canvas = text_holder.lockCanvas();
   //判断若画板为空则跳出循环
            if (canvas == null) {
              break;
            }
        //设置画布颜色,透明
 canvas.drawColor(PixelFormat.TRANSPARENT, PorterDuff.Mode.CLEAR);
 //用循环来你的弹幕集合并且在画板上展示出来
 //x =20为你的弹幕在不断的从左到右移动
      for (Danmu danmu : list) {
  canvas.drawText(danmu.text, danmu.x  = 20, danmu.y, paint);
  //若移动的位置大于视频Surface的宽度了就归0
     if (danmu.x > sv_media.getWidth()) {
                danmu.x = 0;
           }
          }
          //将画布解锁并显示到屏幕上
    text_holder.unlockCanvasAndPost(canvas);
          }
        }
      }.start();//不要忘记开启线程

    }

  }

public void Gogo(View view) {
//先判断输入框里有没有东西
    if (!editText.getText().toString().isEmpty() && !editText.getText().toString().equals("")) {
      Danmu danmu = new Danmu(editText.getText().toString());
      list.add(danmu);
    }
  }