Android实现随手指移动小球

package com.bwei.self_view;
 
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.WindowManager;
 
/**
 * Created by ZhangTAO on 2017/11/2.
 */
 
public class MyView extends View{
  // 初始化圆的位置
  public int x = 200;
  public int y = 600;
  Context context;
  public MyView(Context context) {
    super(context,null);
    this.context = context;
  }
 
  public MyView(Context context, @Nullable AttributeSet attrs) {
    super(context, attrs,0);
    this.context = context;
  }
 
  public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    initView();
    this.context = context;
  }
 
  private void initView() {
    setBackgroundColor(Color.BLUE);
  }
 
  /**
   * @canvas 画布 paint 画笔
   */
  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    //建立一根画笔
    Paint paint = new Paint();
    paint.setStyle(Paint.Style.FILL);
    paint.setColor(Color.RED);
    paint.setFakeBoldText(true);
    //画布
    canvas.drawCircle(DipUtils.dip(getContext(),x),
        DipUtils.dip(getContext(),y),
        DipUtils.dip(getContext(),50),paint);
 
  }
  /**
   * 进行设置touch移动
   */
  @Override
  public boolean onTouchEvent(MotionEvent event) {
    super.onTouchEvent(event);
    int action = event.getAction();
    switch (action) {
      case MotionEvent.ACTION_DOWN :
      case MotionEvent.ACTION_MOVE :
      case MotionEvent.ACTION_UP :
        //获取当前触摸点的x,y坐标
        x = (int) event.getX();
        y = (int) event.getY();
        invalidate();
        break;
    }
//    获取屏幕的宽高
    WindowManager manger = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    int width = manger.getDefaultDisplay().getWidth();
    int height = manger.getDefaultDisplay().getHeight();
    //重新绘制圆 ，控制小球不会被移除屏幕
    if(x>=20 && y>=20 && x<=width-20 && y<height-20) {
      invalidate();
    }
      //自己处理触摸事件
     return true;
    //修改当前的坐标
//    this.x =(int) event.getX();
//    this.y =(int) event.getY();
    //重绘小球
//    this.invalidate();
//    return true;
  }
}