自定义View可跟手指移动

转载https://blog.youkuaiyun.com/jiahui6666/article/details/83719306

创建项目

自定义View

public class globlue extends View {
    private Paint mPaint;
    private int x;
    private int y;
    private int startX;
    private int startY;
    private boolean mBall;

    public globlue(Context context) {
        super(context);
    }

    public globlue(Context context,  AttributeSet attrs) {
        super(context, attrs);

    }

    public globlue(Context context,  AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, 0);
        initView();
    }
    private void initView(){
//        实例画笔对象
        mPaint= new Paint();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
//        初始化View位置
        int width=this.getWidth();
        int height=this.getHeight();
        x=width/2;
        y=height/2;
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
    }

    private static int RADIUS=50;

    @Override
    protected void onDraw(Canvas canvas) {
        mPaint.setColor(Color.BLUE);
        canvas.drawCircle(x,y,RADIUS,mPaint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                startX = (int) event.getX();
                startY = (int) event.getY();
//              是否触摸到View
                mBall = isBall(startX, startY);

                break;
            case MotionEvent.ACTION_MOVE:
                if (mBall) {
                    x = (int) event.getX();
                    y = (int) event.getY();
//                   刷新界面，调用onDraw（）
                    postInvalidate();
                }
                break;
            case MotionEvent.ACTION_UP:
                break;
            default:
                break;
        }
        return true;
    }

    public boolean isBall(int startX,int startY){

        double sqrt=Math.sqrt((startX-x)*(startX-x)+(startY-y)*(startY-y));
        if(sqrt<RADIUS){
            return true;
        }
        return false;
    }
    
}

在布局文件中添加自定义控件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <com.example.gn.viewdemo.globlue
        android:id="@+id/view"
        android:layout_height="wrap_content"
        android:layout_width="wrap_content"
    />
</LinearLayout>

    运行项目效果