How to differentiate top windows in iOS8?

问题

Following the strategy from this SO answer, in iOS 7 I could find the top window in my app like so:

UIWindow *topWindow = [[[UIApplication sharedApplication].windows sortedArrayUsingComparator:^NSComparisonResult(UIWindow *win1, UIWindow *win2) {
    return win1.windowLevel - win2.windowLevel;
}] lastObject];

However, since iOS8 there may be one or more UITextEffectsWindows which may be the lastObject in the above strategy. No good.

Initially I could run a predicate filter on the array of windows and test which windows are UIWindows like so:

NSPredicate *filter = [NSPredicate predicateWithBlock:^BOOL(id obj, NSDictionary *bind) {
    return [obj isMemberOfClass:[UIWindow class]];
}];

However, the top UIWindow may not be UIWindow, but some subclass like NRWindow. Here is an example:

[[NRWindow class] isKindOfClass:[UIWindow class]]; // true
[[UITextEffectsWindow class] isKindOfClass:[UIWindow class]]; // true

My question is this: How can I safely differentiate/find the top UIWindow subclass so I can do things like

[[topWindow rootViewController] presentViewController:mailComposer animated:YES completion:nil];

(Note: Testing for UITextEffectsWindow directly is frowned upon, and [[UIApplication sharedApplication] keyWindow] unfortunately isn't reliable.)

回答1:

I assume that you only want to present from windows that you have created. So you could:

Write a subclass of UIWindow and use that when creating your windows. Then you can test for windows of that subclass.
Add an associated object to all windows that are eligible for presenting a modal view. Then you can test for the associated object when searching for a window.

来源：https://stackoverflow.com/questions/31375915/how-to-differentiate-top-windows-in-ios8

标签

ios

objective-c

ios8

uiwindow