UIModalPresentationCurrentContext with Transition?

问题:

I am trying to modal present a view controller like below:

UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
UIViewController *vc = [storyboard instantiateViewControllerWithIdentifier:@"addPopover"];
vc.view.backgroundColor = [UIColor clearColor];
self.modalPresentationStyle = UIModalPresentationCurrentContext;
[self presentModalViewController:vc animated:YES];

Now using UIModalPresentationCurrentContext means I can present this view with a transparent background and see my other view behind the new one. However, it stops me from being able to present it with a transition.

Any ideas why? Or how I can get around this? Thanks.

回答1:

Full screen modals aren't supposed to allow you to see the under layer. Annoying I know.

From your code I'm assuming that "addPopover" is actually a full screen view, where you have your content as a subsection while the rest is transparent.

Try this:

vc.modalPresentationStyle = UIModalPresentationCurrentContext;
vc.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
[self presentViewController:vc animated:YES completion:NULL];

Note: I'd recommend adding a low alpha background color to let the user know that they can't interact with the rest of the view when you pop this over top...

回答2:

I was able to accomplish this by setting modalPresentationStyle = UIModalPresentationCurrentContext on the rootViewController of my UIWindow, IF I haven't presented any new full screen viewControllers on top of this rootViewController. I did something like this:

UIViewController *rootViewController = [UIApplication sharedApplication].delegate.window.rootViewController;
rootViewController.modalPresentationStyle = UIModalPresentationCurrentContext;
[self presentViewController:vc animated:YES completion:nil];

I've tried this with both a UINavigationController as my window's rootViewController and various other custom view controllers. It seems as long as the window's rootViewController knows what's going on, any sub-viewControllers can call presentViewController:animated:completion: without blacking-out the underlying view.

However, let's say you present another viewController on top of your window's rootViewController. And this new viewController is presented with modalPresentationStyle = UIModalPresentationFullScreen (ie. takes up the screen), then you have to call modalPresentationStyle = UIModalPresentationCurrentContext on that top-most viewController.

So to recap:

• If you have UINavigationController -> UIViewController(s) (they could be pushed and popped in and out), then you set modalPresentationStyle = UIModalPresentationCurrentContext on the UINavigationController.
• If you have UINavigationController -> UIViewController -> new-UIViewController (with modalPresentationStyle set to UIModalPresentationFullScreen), then you set modalPresentationStyle = UIModalPresentationCurrentContext on the new-UIViewController.

Hopefully this works for you guys as well!

回答3:

Mr. T's suggestions worked nearly perfectly, you just lose the transition animation on the presented viewcontroller

Since it is also setting the appDelegates rootviewController's presentation style, it will also remove the transition animations for any views presented from that point.

My fix was to return the AppDelegates rootViewController's presentation style back to it's default whenever the viewcontroller is closed that I needed the transparent background on

I have a button that dismisses the presentedViewController, in that I also set the presentation style of the rootViewController back to default using:

    UIViewController *rootViewController = [[[[UIApplication sharedApplication] delegate] window] rootViewController];
    rootViewController.modalPresentationStyle = UIModalPresentationFullScreen;

I hope that helps anyone else getting stumped on this problem.