使用SurfaceView实现视频弹幕

package com.example.app2;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PixelFormat;
import android.graphics.PorterDuff;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity implements SurfaceHolder.Callback {
  private SurfaceView mSvVideo;
  private SurfaceView mSvDanMu;
  private EditText mEd;
  private MediaPlayer mediaPlayer;
  private SurfaceHolder svVideoHolder, svDanMuHolder;
  private boolean isPlay = true;
  List<DanMuBean> list = new ArrayList<>();
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    // 创建MediaPlayer
    initPlayer();
    // 初始化视图
    initView();
  }
  private void initPlayer() {
    if (mediaPlayer == null) {
      mediaPlayer = new MediaPlayer();
    }
    // 重置
    mediaPlayer.reset();
    try {
      mediaPlayer.setDataSource("http://clips.vorwaerts-gmbh.de/big_buck_bunny.mp4");
      mediaPlayer.prepareAsync(); //异步准备
      mediaPlayer.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {
        @Override
        public void onPrepared(MediaPlayer mp) {
          mediaPlayer.setLooping(true); //是否开启循环播放
          mediaPlayer.start(); //开始播放
        }
      });
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
  /**
   * 发送的信息
   *
   * @param view
   */
  public void send(View view) {
    submit();
  }
  private void submit() {
    // validate 非空判断
    String edString = mEd.getText().toString().trim();
    if (TextUtils.isEmpty(edString)) {
      Toast.makeText(this, "edString不能为空", Toast.LENGTH_SHORT).show();
      return;
    }
    list.add(new DanMuBean(edString)); //添加数据
    mEd.setText(""); //清空
  }
  private void initView() {
    mSvVideo = (SurfaceView) findViewById(R.id.sv_video);
    mSvDanMu = (SurfaceView) findViewById(R.id.sv_danMu);
    mEd = (EditText) findViewById(R.id.ed);
    // 初始化 svDanMuHolder svVideoHolder
    svVideoHolder = mSvVideo.getHolder();
    svDanMuHolder = mSvDanMu.getHolder();
    // 添加监听
    svVideoHolder.addCallback(this);
    svDanMuHolder.addCallback(this);
    // 将弹幕显示在最上层, 并设置为透明
    mSvDanMu.setZOrderOnTop(true);
    svDanMuHolder.setFormat(PixelFormat.TRANSPARENT); //PixelFormat: 像素格式, TRANSPARENT(2):透明的; TRANSLUCENT(-3):半透明
  }
  /**
   * surfaceCreated:创建
   *
   * @param holder
   */
  @Override
  public void surfaceCreated(SurfaceHolder holder) {
    if (holder == svVideoHolder) {
      mediaPlayer.setDisplay(svVideoHolder); //将内容显示在 svVideoHolder上
    } else if (holder == svDanMuHolder) {
      // 弹幕设置 开启线程
      new Thread(new Runnable() {
        @Override
        public void run() {
          while (isPlay) { //死循环
            // 得到画笔, 设置属性
            Paint paint = new Paint();
            paint.setStrokeWidth(5); //设置笔画宽度
            paint.setTextSize(30); //设置字体大小
            paint.setColor(Color.GREEN); // 设置颜色
            // 得到画布 通过lockCanvas
            Canvas canvas = svDanMuHolder.lockCanvas();
            if (canvas == null) {
              break;
            }
            // 填充画布的颜色
            canvas.drawColor(PixelFormat.TRANSPARENT, PorterDuff.Mode.CLEAR); //参数1: 设为透明, 参2: PorterDuff.Mode.CLEAR: 所绘制不会提交到画布上
            // 设置弹幕内容
            for (int i = 0; i < list.size(); i++) {
              String text = list.get(i).text;
              canvas.drawText(text, list.get(i).x += 1, list.get(i).y, paint);
              if (list.get(i).x > mSvVideo.getWidth()) {
                list.get(i).x = 0;
              }
            }
            // 提交
            svDanMuHolder.unlockCanvasAndPost(canvas);
          }
        }
      }).start();
    }
  }
  @Override
  public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
  }
  @Override
  public void surfaceDestroyed(SurfaceHolder holder) {
    isPlay = false;
  }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical"
  tools:context=".MainActivity">
  <FrameLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <SurfaceView
      android:id="@+id/sv_video"
      android:layout_width="match_parent"
      android:layout_height="280dp" />
    <SurfaceView
      android:id="@+id/sv_danMu"
      android:layout_width="match_parent"
      android:layout_height="280dp" />
  </FrameLayout>
  <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <EditText
      android:id="@+id/ed"
      android:layout_width="0dp"
      android:layout_height="wrap_content"
      android:layout_weight="1" />
    <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:onClick="send"
      android:text="弹幕" />
  </LinearLayout>
</LinearLayout>