如何在activity上画一个圆并且不断增大

怎么在activity上画一个圆并且不断增大?
怎么在activity上画一个圆圈，点下按钮后圆圈不断变大，变化过程流畅一点，就像水面涟漪一样？

[解决办法]
我试着写了一个,定义一个view,然后通过thread每隔1秒左右去draw这个圆圈，
下面是代码

MyView

Java code

package wyf.ytl;import android.view.View;import android.graphics.Paint;import android.content.Context;import android.util.AttributeSet;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.RectF;public class MyView extends View {    int iCycle = 0;    //圆的半径10    int r = 10;    // x,y坐标，320屏幕宽度，390屏幕高度，圆的直径20    int x = (320-2*r*0)/2;    int y = (390-2*r*0)/2;        public MyView(Context context,AttributeSet attrs){        super(context,attrs);    }    public MyView(Context context){        super(context);    }        protected void onDraw(Canvas canvas){        super.onDraw(canvas);        Paint paint = new Paint();        paint.setColor(Color.WHITE);                if(iCycle < 5){            iCycle++;        } else {            iCycle = 0;        }                RectF rf1 = new RectF(x-r*iCycle,y-r*iCycle,x+r+r*iCycle,y+r+r*iCycle);        canvas.drawOval(rf1, paint);    }    }