限制超视图边界内子视图的移动 [英] Restrict the movement of subview inside superview bounds

问题描述

我有一个UIView，这是我的VC视图（self.view），我在其中添加了另一个UIView作为子视图，看起来像一个正方形。我想限制superview里面的子视图的移动。基本上子视图不应超出超视范围。

我确实实现了

I have a UIView which is my VC's view(self.view) inside which I have another UIView added as subview both looks like a square. I would like to limit the movement of subview inside the superview. Basically the subview should not go outside the superview bounds.
I did implement

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { 
// i check if point of touch is inside my superview i set the center i.e
UITouch *touch = [[UITouch allObjects] firstObject];
if (CGRectContainsPoint(subview.frame, [touch locationInView:self.view])) {
// set the center here... i.e
subview.center = [touch locationInView:self.view];
}

此作品和子视图正在移动，但它也移动到超级视图之外;我怎样才能限制超视图中的移动？

This works and subview is moving but it also moves outside the superview; how can I restrict the movement within the superview only?

我甚至尝过类似的东西。

I even tried something like .

if (CGRectContainsRect(self.view.bounds, subview.frame)) {
// this condition works but i don't know why my subview sticks to the sides of superview if i try to drag it through the bounds of superview
}

我不这样做在的touchesBegan，touchesCancelled，并没有任何相关的touchesEnd为好。

I don't do anything in touchesBegan, touchesCancelled, and nothing relevant in touchesEnd as well.

推荐答案

您需要检查要移动的视图的新框架，并将其边缘与其超视图的边界进行比较：

You need to check the "new frame" of the view you are moving, and compare its edges to the bounds of its superview:

@implementation DraggableView

- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    // restrict to superview bounds
    CGRect parentFrame = [self.superview bounds];

    UITouch *aTouch = [touches anyObject];
    CGPoint location = [aTouch locationInView:self];
    CGPoint previousLocation = [aTouch previousLocationInView:self];

    // new frame for this "draggable" subview, based on touch offset when moving
    CGRect newFrame = CGRectOffset(self.frame, (location.x - previousLocation.x), (location.y - previousLocation.y));

    if (newFrame.origin.x < 0) {

        // if the new left edge would be outside the superview (dragging left),
        // set the new origin.x to Zero
        newFrame.origin.x = 0;

    } else if (newFrame.origin.x + newFrame.size.width > parentFrame.size.width) {

        // if the right edge would be outside the superview (dragging right),
        // set the new origin.x to the width of the superview - the width of this view
        newFrame.origin.x = parentFrame.size.width - self.frame.size.width;

    }

    if (newFrame.origin.y < 0) {

        // if the new top edge would be outside the superview (dragging up),
        // set the new origin.y to Zero
        newFrame.origin.y = 0;

    } else if (newFrame.origin.y + newFrame.size.height > parentFrame.size.height) {

        // if the new bottom edge would be outside the superview (dragging down),
        // set the new origin.y to the height of the superview - the height of this view
        newFrame.origin.y = parentFrame.size.height - self.frame.size.height;

    }

    // update this view's frame
    self.frame = newFrame;
}

@end

这也使用了触摸，而不是在触摸上居中视图（因此当你开始拖动时它不会跳到你的手指）。

This also uses the offset of the touch, instead of centering the view on the touch (so it doesn't "jump to your finger" when you start dragging).

编辑以便澄清：在此图片中，蓝色视图类为 DraggableView ...无法将其拖出超级视图（红色视图）。

Edit for clarification: In this image, the Blue view class is DraggableView... It cannot be dragged outside of its superView (the Red view).

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