Android在 onDraw 事件处理绘图,
初始化的时候就会调用onDraw()
而 invalidate() 函数可以再一次触发onDraw事件,

然后再一次进行绘图动作。[java]
public class DrawCircle extends Activity {

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

setContentView( new View(null){

Paint vPaint = new Paint(); //绘制样式物件
private int i = 0; //弧形角度

@Override
protected void onDraw (Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);

// 设定绘图样式
vPaint.setColor( 0xff00ffff ); //画笔颜色
vPaint.setAntiAlias( true ); //反锯齿
vPaint.setStyle( Paint.Style.STROKE );

// 绘制一个弧形
canvas.drawArc(new RectF(60, 120, 260, 320), 0, i, true, vPaint );

// 弧形角度
if( (i+=10) > 360 )
i = 0;

// 重绘, 再一次执行onDraw 程序
invalidate();
}
});
}
}[/java]