解决 UIAlterController 不居中问题

最后更新：2017-06-30

现象描述

新公司做的解决的第一个bug 就是 UIAlterController 不居中，莫名其妙的飞出屏幕之外

找了很久的答案，最终在苹果论坛看到了相关的描述

We have noticed this in an app when we attempt to present a view from the current "top-most" view. If a UIAlertController happens to be the top-most view we get this behavior. We have changed our code to simply ignore UIAlertControllers, but I'm posting this in case others hit the same issue (as I couldn't find anything).

我们注意到，当我们试图从“top-most”的view present 一个view 时候，当 UIAlertController 刚还是 ““top-most”” 的视图，就会出现这个情况

解决方案:

OC:

在 UIAlertControllers分类里面写

/*
 * UIAlertControllers (of alert type, and action sheet type on iPhones/iPods) get placed in crazy
 * locations when you present a view controller over them.  This attempts to restore their original placement.
 */
- (void)_my_fixupLayout
{
    if (self.preferredStyle == UIAlertControllerStyleAlert && self.view.window)
    {
        CGRect myRect = self.view.bounds;
        CGRect windowRect = [self.view convertRect:myRect toView:nil];
        if (!CGRectContainsRect(self.view.window.bounds, windowRect) || CGPointEqualToPoint(windowRect.origin, CGPointZero))
        {
            CGPoint center = self.view.window.center;
            CGPoint myCenter = [self.view.superview convertPoint:center fromView:nil];
            self.view.center = myCenter;
        }
    }
    else if (self.preferredStyle == UIAlertControllerStyleActionSheet && self.traitCollection.userInterfaceIdiom == UIUserInterfaceIdiomPhone && self.view.window)
    {
        CGRect myRect = self.view.bounds;
        CGRect windowRect = [self.view convertRect:myRect toView:nil];
        if (!CGRectContainsRect(self.view.window.bounds, windowRect) || CGPointEqualToPoint(windowRect.origin, CGPointZero))
        {
            UIScreen *screen = self.view.window.screen;
            CGFloat borderPadding = ((screen.nativeBounds.size.width / screen.nativeScale) - myRect.size.width) / 2.0f;
            CGRect myFrame = self.view.frame;
            CGRect superBounds = self.view.superview.bounds;
            myFrame.origin.x = CGRectGetMidX(superBounds) - myFrame.size.width / 2;
            myFrame.origin.y = superBounds.size.height - myFrame.size.height - borderPadding;
            self.view.frame = myFrame;
        }
    }
}

- (void)viewWillLayoutSubviews
{
    [super viewWillLayoutSubviews];
    [self _my_fixupLayout];
}

SWIFT

extension UIAlertController {
    open override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        fixupLayout()
    }

    private func fixupLayout() {
        if preferredStyle == .alert && view.window != nil {

            let myRect = view.bounds
            let windowRect = view.convert(myRect, to: nil)

            guard let window = view.window else {
                return
            }

            guard let superview = view.superview else {
                return
            }

            if !window.bounds.contains(windowRect) || windowRect.origin.equalTo(CGPoint.zero) {
                let myCenter = superview.convert(window.center, from: nil)
                view.center = myCenter
            }

        } else if preferredStyle == .actionSheet && self.traitCollection.userInterfaceIdiom == .phone && view.window != nil {
            let myRect = view.bounds
            let windowRect = view.convert(myRect, to: nil)

            guard let window = view.window else {
                return
            }

            guard let superview = view.superview else {
                return
            }

            if !(window.bounds.contains(windowRect)) || windowRect.origin.equalTo(CGPoint.zero) {
                let screen = window.screen
                let borderPadding = ((screen.nativeBounds.width / screen.nativeScale) - myRect.size.width) / 2.0
                var myFrame = view.frame
                let superBounds = superview.bounds
                myFrame.origin.x = superBounds.maxX - myFrame.width / 2
                myFrame.origin.y = superBounds.height - myFrame.height - borderPadding
                self.view.frame = myFrame
            }
        }
    }
}

参考

• Apple Solution: http://openradar.appspot.com/19037589

• https://stackoverflow.com/questions/27028983/uialertcontroller-is-moved-to-buggy-position-at-top-of-screen-when-it-calls-pre