1. 定義

在Android系統(tǒng)中，有一種特殊的視圖，稱為SurfaceView，它擁有獨(dú)立的繪圖表面，即它不與其宿主窗口共享同一個繪圖表面。由于擁有獨(dú)立的繪圖表面，因此SurfaceView的UI可以在一個獨(dú)立的線程中進(jìn)行繪制，且不會占用主線程資源。SurfaceView一方面可以實現(xiàn)復(fù)雜而高效的UI，另一方面又不會導(dǎo)致用戶輸入無法得到響應(yīng)。

2. view、surfaceview和GLsurfaceview的區(qū)別

• View：顯示視圖，內(nèi)置畫布，提供圖形繪制函數(shù)、觸屏事件、按鍵事件函數(shù)等；必須在UI主線程內(nèi)更新畫面，速度較慢。
• SurfaceView : 基于view視圖進(jìn)行拓展的視圖類，更適合2D游戲的開發(fā)；是view的子類，類似使用雙緩機(jī)制，在新的線程中更新畫面所以刷新界面速度比view快。
• GLSurfaceView：基于SurfaceView視圖再次進(jìn)行拓展的視圖類，專用于3D游戲開發(fā)的視圖；是SurfaceView的子類，openGL專用。

3. Surface的使用

• Surface與MediaPlayer實現(xiàn)視頻播放

public class SurfaceViewActivity extends AppCompatActivity implements SurfaceHolder.Callback, MediaPlayer.OnPreparedListener {
    private SurfaceView surfaceView;
    private SurfaceHolder surfaceHolder;
    private MediaPlayer mediaPlayer;
    private static final String VIDEO_PATH = "https://inducesmile.com/wp-content/uploads/2016/05/small.mp4";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_surface_view);
        surfaceView = (SurfaceView) findViewById(R.id.surfaceView);
        //獲取到SurfaceHolder對象
        surfaceHolder = surfaceView.getHolder();
        //設(shè)置其生命周期監(jiān)聽
        surfaceHolder.addCallback(this);
    }

    //創(chuàng)建SurfaceView時被調(diào)用
    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        mediaPlayer = new MediaPlayer();
        mediaPlayer.setDisplay(surfaceHolder); //將SurfaceView與MediaPlayer進(jìn)行綁定
        try {
            mediaPlayer.setDataSource(VIDEO_PATH);
            mediaPlayer.prepare();
            mediaPlayer.setOnPreparedListener(this);
            mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    //SurfaceView大小尺寸改變時調(diào)用，比如橫豎屏切換
    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

    }

    //SurfaceView被銷毀時被調(diào)用
    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        releaseMediaPlayer();
    }

    //音頻播放準(zhǔn)備好后，開始播放
    @Override
    public void onPrepared(MediaPlayer mp) {
        mediaPlayer.start();
    }

    @Override
    protected void onPause() {
        super.onPause();
        releaseMediaPlayer();
    }

    @Override
    protected void onStop() {
        super.onStop();
        releaseMediaPlayer();
    }

    //釋放MediaPlayer對象
    private void releaseMediaPlayer(){
        if (mediaPlayer != null){
            mediaPlayer.release();
            mediaPlayer = null;
        }
    }
}

首先根據(jù)SurfaceView獲取到其SurfaceHolder對象，然后添加SurfaceHolder的監(jiān)聽事件，在SurfaceView被創(chuàng)建時，調(diào)用mediaPlayer.setDisplay(surfaceHolder);將SurfaceView和MediaPlayer進(jìn)行綁定。

• SurfaceView實現(xiàn)動畫效果

public class SinSurfaceView extends SurfaceView implements Runnable{
    private SurfaceHolder mSurfaceHolder;
    private Paint mPaint; //畫筆對象
    private Path mPath; //路徑

    public SinSurfaceView(Context context) {
        super(context);
        init();
    }

    public SinSurfaceView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

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

    //初始化
    private void init(){
        //設(shè)置畫筆
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(5);
        mPaint.setColor(Color.GREEN);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        //設(shè)置路徑
        mPath = new Path();
        //獲取到SurfaceHolder對象
        mSurfaceHolder = getHolder();
        //設(shè)置其監(jiān)聽事件
        mSurfaceHolder.addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(SurfaceHolder holder) {
                //開啟線程，進(jìn)行繪制
                new Thread(SinSurfaceView.this).start();
            }

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

            }

            @Override
            public void surfaceDestroyed(SurfaceHolder holder) {
                isDrawing = false;  //設(shè)置為false，表示停止繪制
                mSurfaceHolder.removeCallback(this); //將callback移除 
            }
        });
    }
    //是否進(jìn)行繪制標(biāo)識，默認(rèn)為false
    private volatile boolean isDrawing = true;
    private int drawX, drawY;

    @Override
    public void run() {
        //當(dāng)允許繪制時，則不斷進(jìn)行繪制
        while (isDrawing){
            drawX ++;
            drawY = (int)(100*Math.sin(drawX*2*Math.PI / 180) + 400);
            mPath.lineTo(drawX, drawY);
            draw();
        }
    }

    //將path對象繪制到canvas中
    private void draw(){
        Canvas canvas = null;
        try {
            //獲取到canvas對象
            canvas = mSurfaceHolder.lockCanvas();
            if (canvas != null){
                canvas.drawColor(Color.WHITE);
                canvas.drawPath(mPath, mPaint);
            }
        } finally {
            if (canvas != null){
                //釋放canvas對象
                mSurfaceHolder.unlockCanvasAndPost(canvas);
            }
        }

    }
}

3. SurfaceView原理