1. 定义
在Android系统中，有一种特殊的视图，称为SurfaceView，它拥有独立的绘图表面，即它不与其宿主窗口共享同一个绘图表面。由于拥有独立的绘图表面，因此SurfaceView的UI可以在一个独立的线程中进行绘制，且不会占用主线程资源。SurfaceView一方面可以实现复杂而高效的UI，另一方面又不会导致用户输入无法得到响应。
2. view、surfaceview和GLsurfaceview的区别
- View：显示视图，内置画布，提供图形绘制函数、触屏事件、按键事件函数等；必须在UI主线程内更新画面，速度较慢。
- SurfaceView : 基于view视图进行拓展的视图类，更适合2D游戏的开发；是view的子类，类似使用双缓机制，在新的线程中更新画面所以刷新界面速度比view快。
- GLSurfaceView：基于SurfaceView视图再次进行拓展的视图类，专用于3D游戏开发的视图；是SurfaceView的子类，openGL专用。
3. Surface的使用
- Surface与MediaPlayer实现视频播放
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);
//获取到SurfaceHolder对象
surfaceHolder = surfaceView.getHolder();
//设置其生命周期监听
surfaceHolder.addCallback(this);
}
//创建SurfaceView时被调用
@Override
public void surfaceCreated(SurfaceHolder holder) {
mediaPlayer = new MediaPlayer();
mediaPlayer.setDisplay(surfaceHolder); //将SurfaceView与MediaPlayer进行绑定
try {
mediaPlayer.setDataSource(VIDEO_PATH);
mediaPlayer.prepare();
mediaPlayer.setOnPreparedListener(this);
mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
} catch (IOException e) {
e.printStackTrace();
}
}
//SurfaceView大小尺寸改变时调用，比如横竖屏切换
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
}
//SurfaceView被销毁时被调用
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
releaseMediaPlayer();
}
//音频播放准备好后，开始播放
@Override
public void onPrepared(MediaPlayer mp) {
mediaPlayer.start();
}
@Override
protected void onPause() {
super.onPause();
releaseMediaPlayer();
}
@Override
protected void onStop() {
super.onStop();
releaseMediaPlayer();
}
//释放MediaPlayer对象
private void releaseMediaPlayer(){
if (mediaPlayer != null){
mediaPlayer.release();
mediaPlayer = null;
}
}
}
首先根据SurfaceView获取到其SurfaceHolder对象，然后添加SurfaceHolder的监听事件，在SurfaceView被创建时，调用mediaPlayer.setDisplay(surfaceHolder);将SurfaceView和MediaPlayer进行绑定。
- SurfaceView实现动画效果
public class SinSurfaceView extends SurfaceView implements Runnable{
private SurfaceHolder mSurfaceHolder;
private Paint mPaint; //画笔对象
private Path mPath; //路径
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(){
//设置画笔
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeWidth(5);
mPaint.setColor(Color.GREEN);
mPaint.setStrokeJoin(Paint.Join.ROUND);
//设置路径
mPath = new Path();
//获取到SurfaceHolder对象
mSurfaceHolder = getHolder();
//设置其监听事件
mSurfaceHolder.addCallback(new SurfaceHolder.Callback() {
@Override
public void surfaceCreated(SurfaceHolder holder) {
//开启线程，进行绘制
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; //设置为false，表示停止绘制
mSurfaceHolder.removeCallback(this); //将callback移除
}
});
}
//是否进行绘制标识，默认为false
private volatile boolean isDrawing = true;
private int drawX, drawY;
@Override
public void run() {
//当允许绘制时，则不断进行绘制
while (isDrawing){
drawX ++;
drawY = (int)(100*Math.sin(drawX*2*Math.PI / 180) + 400);
mPath.lineTo(drawX, drawY);
draw();
}
}
//将path对象绘制到canvas中
private void draw(){
Canvas canvas = null;
try {
//获取到canvas对象
canvas = mSurfaceHolder.lockCanvas();
if (canvas != null){
canvas.drawColor(Color.WHITE);
canvas.drawPath(mPath, mPaint);
}
} finally {
if (canvas != null){
//释放canvas对象
mSurfaceHolder.unlockCanvasAndPost(canvas);
}
}
}
}
