在activity中onCreate里，直接操作surfaceview，是无法成功的。
像以下代码：
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.trace);
TraceView=(SurfaceView) findViewById(R.id.TraceView);
TraceViewHolder=TraceView.getHolder();Canvas canvas = TraceViewHolder.lockCanvas();
canvas.drawColor(Color.WHITE); //设置背景颜色
Paint p = new Paint();
p.setStyle(Style.STROKE);
p.setStrokeWidth(2);
p.setColor(Color.BLUE);
canvas.drawLine(10, 0,10, 400, p);
if (canvas!=null) TraceViewHolder.unlockCanvasAndPost(canvas);
}
运行完后，surfaceview里黑乎乎一片，没有想要的线条。
要添加 surfaceviewHolder的Callback函数，才能实现。代码如下:
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.trace);
TraceView=(SurfaceView) findViewById(R.id.TraceView);
///////////////三个函数缺一不可。surfaceCreated， surfaceChanged，surfaceDestroyed /////
TraceView.getHolder().addCallback(new Callback() {
public void surfaceCreated(SurfaceHolder holder) {
Canvas canvas = holder.lockCanvas();
canvas.drawColor(Color.WHITE); //设置背景颜色
Log.i("TraceView Callback","OK");
Paint p = new Paint();
p.setStyle(Style.STROKE);
p.setStrokeWidth(1);
p.setColor(Color.BLUE);
// canvas.drawLine(20, 0,20, 400, p);
DrawGrid(canvas,p,10);
if (canvas!=null) holder.unlockCanvasAndPost(canvas);
}
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height){
// Log.i("TraceView Changed Callback","OK");
}
public void surfaceDestroyed(SurfaceHolder holder){
}
});
/////////////////////////
}