Rect的intersect 方法坑

在使用android 做一些小游戏的时候，可能需要用到碰撞检测，而矩形的
Rect.intersect(Rect a)方法可能被用到
但是需要注意的是：这个方法是用来取两个矩形的相交部分，并设置给Rect

    /**
     * If the rectangle specified by left,top,right,bottom intersects this
     * rectangle, return true and set this rectangle to that intersection,
     * otherwise return false and do not change this rectangle. No check is
     * performed to see if either rectangle is empty. Note: To just test for
     * intersection, use {@link #intersects(Rect, Rect)}.
     *
     * @param left The left side of the rectangle being intersected with this
     *             rectangle
     * @param top The top of the rectangle being intersected with this rectangle
     * @param right The right side of the rectangle being intersected with this
     *              rectangle.
     * @param bottom The bottom of the rectangle being intersected with this
     *             rectangle.
     * @return true if the specified rectangle and this rectangle intersect
     *              (and this rectangle is then set to that intersection) else
     *              return false and do not change this rectangle.
     */
    @CheckResult
    public boolean intersect(int left, int top, int right, int bottom) {
        if (this.left < right && left < this.right && this.top < bottom && top < this.bottom) {
            if (this.left < left) this.left = left;
            if (this.top < top) this.top = top;
            if (this.right > right) this.right = right;
            if (this.bottom > bottom) this.bottom = bottom;
            return true;
        }
        return false;
    }
    

如果不知道这一点，在写游戏时会发现有时候碰撞检测没有作用，很是恼火。
正确的应该使用这一个方式：

    /**
     * Returns true if this rectangle intersects the specified rectangle.
     * In no event is this rectangle modified. No check is performed to see
     * if either rectangle is empty. To record the intersection, use intersect()
     * or setIntersect().
     *
     * @param left The left side of the rectangle being tested for intersection
     * @param top The top of the rectangle being tested for intersection
     * @param right The right side of the rectangle being tested for
     *              intersection
     * @param bottom The bottom of the rectangle being tested for intersection
     * @return true iff the specified rectangle intersects this rectangle. In
     *              no event is this rectangle modified.
     */
    public boolean intersects(int left, int top, int right, int bottom) {
        return this.left < right && left < this.right && this.top < bottom && top < this.bottom;
    }

在调试时，可以将Rect 以红色画出来，方便观察。