iphone - Constrain Drag UIButton on diagonal path

Question

How can I constrain the drag-path of a button so that it can only be dragged to the centre of the screen from any point I want?

I know the current position of the UIButton and the centre coordinates. I need the current x and y formula for the drag event.

Answer 1

这应该这样做。保存拖动的开始位置，获取每个移动事件的当前位置。将它们传递给这个函数。它将回答一个可以应用于按钮框架的向量。

计算的要点是通过选择阻力的最小分量（x 或 y）并回答在两个维度上具有相同大小的向量（保留两个轴上的符号）来确定大小。

// answer a vector to apply to an object's frame, constrained to a diagonal
- (CGPoint)constrainToDiagonalFrom:(CGPoint)from to:(CGPoint)to {

    CGPoint diff = CGPointMake(to.x-from.x, to.y-from.y);
    CGFloat magnitude = MIN(fabs(diff.x), fabs(diff.y));    // this is how large the drag will be
    return CGPointMake(copysignf(magnitude, diff.x), copysignf(magnitude, diff.y));
}

像这样称呼它：

// on touches moved
// we saved startPoint on touches began
// get location from this event's touches

CGPoint diagonal = [self constrainToDiagonalFrom:startPoint to:location];
myButton.frame = CGRectOffset(myButton.frame, diagonal.x, diagonal.y);

您可以随意计算幅度。最大分量，最小分量，平均值等。只要结果在两个维度上都是对称的。

Answer 2

你的意思是像：

if ((oldX - newX) < oldX && (oldY - newY) < oldY) {
    updatePosition(newX, newY);
}

Answer 3

在拖动事件中放置一个条件。如果它被拖动到您需要的位置，则移动它；否则什么都不做。