Android:如何确定触摸事件是否在圈中? [英] Android: How to determine if a touch event is in a circle?

问题描述

我想在触摸圆形区域时播放媒体，但是如何确定触摸位置在圆圈中呢?

I want to play a media when i touch a circular area, but how can I could determine that my touch position is in the circle?

到目前为止，我扩展了view并实现了onTouchEvent，并且我需要一种算法来确定位置是在圆内还是圆外.

So far I extend a view and implement the onTouchEvent, and I need the algorithm for deciding if the position is inside or outside the circle.

推荐答案

您应该使用 MotionEvent获取xTouch和yTouch .getX()和 MotionEvent.getY( )，并检查是否:

You should take position of the view with View.getX() and View.getY() to get x and y of the upper left corner and also assuming You know the radius (or able to obtain width/height of the view to determine radius). After that, obtain xTouch and yTouch using MotionEvent.getX() and MotionEvent.getY() and check if:

double centerX = x + radius;
double centerY = y + radius;
double distanceX = xTouch - centerX;
double distanceY = yTouch - centerY;

boolean isInside() {
    return (distanceX * distanceX) + (distanceY * distanceY) <= radius * radius;
}

该公式只是对学校几何形状的解释，以确定点是否在圆形区域内.有关更多详细信息，请参考笛卡尔坐标系的圆方程.

The formula is just interpretation of schools geometry for determining if dot is inside circle area or not. Refer to circle equation for Cartesian coordinates for more details.

值的解释是:

(x + radius)和(y + radius)是圆的中心.

(xTouch - (x + radius))是触摸点到中心的距离X.

(xTouch - (x + radius)) is distance from touch point to center by X.

(yTouch - (y + radius))是触摸点到中心的距离，以Y为单位.

(yTouch - (y + radius)) is distance from touch point to center by Y.

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