android 拖动圆形控件 滑动到屏幕边缘随机改变颜色

public class MainActivity extends AppCompatActivity implements View.OnTouchListener {

Button button;
GradientDrawable drawable;
int screenWidth = 0;
int screenHeight = 0;
int lastX = 0;
int lastY = 0;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

DisplayMetrics dm = getResources().getDisplayMetrics();
screenWidth = dm.widthPixels;
screenHeight = dm.heightPixels - 50;

button = (Button) findViewById(R.id.btn_hh);
drawable = (GradientDrawable) button.getBackground();

button.setOnTouchListener(this);
}

@Override
public boolean onTouch(View v, MotionEvent event) {
// 随机改变颜色
Random random = new Random();
int ranColor = 0;
int ea=event.getAction();

switch(ea){
case MotionEvent.ACTION_DOWN:
lastX = (int) event.getRawX();
lastY = (int) event.getRawY();
break;
/**
* layout(l,t,r,b)
* l  Left position, relative to parent
t  Top position, relative to parent
r  Right position, relative to parent
b  Bottom position, relative to parent
* */
case MotionEvent.ACTION_MOVE:
int dx =(int)event.getRawX() - lastX;
int dy =(int)event.getRawY() - lastY;

int left = v.getLeft() + dx;
int top = v.getTop() + dy;
int right = v.getRight() + dx;
int bottom = v.getBottom() + dy;

if(left < 0){
left = 0;
right = left + v.getWidth();
ranColor = 0xff000000 | random.nextInt(0x00ffffff);
drawable.setColor(ranColor);
}

if(right > screenWidth){
right = screenWidth;
left = right - v.getWidth();
ranColor = 0xff000000 | random.nextInt(0x00ffffff);
drawable.setColor(ranColor);
}

if(top < 0){
top = 0;
bottom = top + v.getHeight();
ranColor = 0xff000000 | random.nextInt(0x00ffffff);
drawable.setColor(ranColor);
}

if(bottom > screenHeight){
bottom = screenHeight;
top = bottom - v.getHeight();
ranColor = 0xff000000 | random.nextInt(0x00ffffff);
drawable.setColor(ranColor);
}

v.layout(left, top, right, bottom);

Log.i("", "position：" + left +", " + top + ", " + right + ", " + bottom);

lastX = (int) event.getRawX();
lastY = (int) event.getRawY();

break;
case MotionEvent.ACTION_UP:

break;
}
return false;
}
}

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="oval">

<!--填充色-->
<solid android:color="#565745"/>

<!-- 设置按钮的四个角为弧形 -->
<!-- android:radius 弧形的半径 -->
<corners android:radius="360dip"/>
</shape>