android自定义视图 按下移动抬起画出直线

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//设置生成的视图信息 把内部视图类传进去
setContentView(new CustomView(this));
}
//内部类中编写
class CustomView extends View{
//定义各个坐标的位置变量
float startX,startY,stopX,stopY;

public CustomView(Context context) {
super(context);
}
//画的方法
@Override
protected void onDraw(Canvas canvas) {
//创建画笔对象
Paint paint = new Paint();
//设置画笔的颜色
paint.setColor(Color.BLACK);
//画直线的方法，把各个点的坐标值传进去
canvas.drawLine(startX, startY, stopX, stopY, paint);
super.onDraw(canvas);
}
//点击事件
@Override
public boolean onTouchEvent(MotionEvent event) {
//选择点击动作
switch (event.getAction()){
//按下
case MotionEvent.ACTION_DOWN:
//设置起点的坐标值
startX = event.getX();
startY = event.getY();
break;
//移动
case MotionEvent.ACTION_MOVE:
// 设置移动时重点坐标的值
stopX = event.getX();
stopY = event.getY();
//强制刷新视图
invalidate();
break;
//抬起
case MotionEvent.ACTION_UP:
//获取抬起的坐标值
stopX = event.getX();
stopY = event.getY();
//强制刷新视图
invalidate();
break;
}
return true;
}

}

}