Adding another view controller's view as subview

Question

I am trying to get a popup effect and want to design the popup view in another view controller so i can use the xib to do it.

When i used the presentViewController or pushViewController and set the background to transparent, i end up seeing the Window's background color.

I tried this code to add subview to the navigation controller's view so that i can have the Info view cover the entire screen with a transparent background. I also have tab bar to cover up as well.

InfoVC *vc = [[InfoVC alloc] initWithNibName:@"InfoVC" bundle:nil];
[self.navigationController.view addSubview:vc.view];

My problem is inside my InfoVC when i try to dismiss it, the app will crash with some EXC_BAD_ACCESS message:

[self.view removeFromSuperview];

EDIT:

I found a way to stop it crashing but setting the InfoVC as a property in the MainVC. I think the reason for crash is when i call "self.view" in the action inside the InfoVC, it doesn't know that self is the InfoVC inside MainVC.

Answer 1

InfoVC *vc = [[InfoVC alloc] initWithNibName:@"InfoVC" bundle:nil];
[self.navigationController.view addSubview:vc.view];

No no no no. Never never do that.

There is an elaborate dance that you must traverse in order to put a view controller's view inside another view controller's view (or remove it afterwards) if it doesn't come with built-in facilities for doing this (the way a UISplitViewController does, or the way a navigation controller manages the views of the view controllers that are pushed and popped within it).

Read up on customer container controllers. One of the examples from my book is here:

https://github.com/mattneub/Programming-iOS-Book-Examples/blob/master/ch19p556containerController/p476containerController/ViewController.m

Answer 2

After a "modally" presented view controller has appeared the views under the now presented view controller will be removed; this saves memory, and eases rendering. In your case, though, you also end up seeing the window behind the "modally" presented view.

The natural, and seemingly logical, next step is to simply take one view controller's view and cram it into another. However, as you have discovered, this is problematic. With the newly inserted view safely retained by the view hierarchy it is safe, but the new view controller is not so lucky, it is quickly deallocated. So when this new view tries to contact its controller you will get an EXC_BAD_ACCESS and crash. One workaround, again as you have found, is to simply have the original view controller keep a strong reference to the new view controller. And this can work... badly. There's still a good chance you will get an UIViewControllerHierarchyInconsistencyException.

Of course if you simply want to add a small view you create in IB you don't need to use a view controller as the "File's Owner" and there are many examples of creating an instance of a view from a xib file.

The more interesting question here is, "How would/does apple do it?" Apple consistently says that a view controller is the correct controller for an encapsulated unit of work. For example, their TWTweetComposeViewController, you present it, and it seems to float. How?

The first way of accomplishing this that comes to my mind is to have a clear background that isn't clear. That is, create an image of the screen before the presented view controller appears and set that as the background before the presenting view is removed. So for example(Explanation to follow):

QuickSheetViewController.xib

QuickSheetViewController.h

#import <UIKit/UIKit.h>
@interface QuickSheetViewController : UIViewController
- (IBAction)dismissButtonPressed:(id)sender;
@end

QuickSheetViewController.m

#import "QuickSheetViewController.h"
#import <QuartzCore/QuartzCore.h>
@implementation QuickSheetViewController {
    UIImage *_backgroundImage;
}
-(void)renderAndSaveBackgroundImageFromVC:(UIViewController *)vc{
    UIGraphicsBeginImageContext(vc.view.bounds.size);
    [vc.view.layer renderInContext:UIGraphicsGetCurrentContext()];
    _backgroundImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
}
-(void)viewWillAppear:(BOOL)animated{
    [super viewWillAppear:animated];
    // save an image of the current view, and set our background to clear so we can see the slide-in.
    [self renderAndSaveBackgroundImageFromVC:self.presentingViewController];
    self.view.backgroundColor = [UIColor clearColor];
}
-(void)viewDidAppear:(BOOL)animated{
    [super viewDidAppear:animated];
    // Time to use our saved background image.
    self.view.backgroundColor = [UIColor colorWithPatternImage:_backgroundImage];
}
-(void)viewWillDisappear:(BOOL)animated{
    [super viewWillDisappear:animated];
    // Set our background to clear so we can see the slide-out.
    self.view.backgroundColor = [UIColor clearColor];
}
- (IBAction)dismissButtonPressed:(id)sender {
    [self dismissViewControllerAnimated:YES completion:nil];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation{
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
@end

The majority of this example hinges upon the renderAndSaveBackgroundImageFromVC: method. In which, we create a graphics context render the view we are about to cover into it, and then create a UIImage to later (in viewDidAppear) use as a background.

Now simply use it like:

QuickSheetViewController *newVC = [[QuickSheetViewController alloc] initWithNibName:nil bundle:nil];
[self presentViewController:newVC animated:YES completion:nil];

You will see through the background just long enough for the animation to happen, then we use our saved image to hide the removal of the presenting view.

Answer 3

You can never have a UIView remove it's subviews, the subviews themselves must remove themselves from it's superview. You can easily loop through subviews and have them removed like so

for (UIView *view in vc.view.subviews) {
  [view removeFromSuperview];
}

Docs for reference: http://developer.apple.com/library/ios/#documentation/uikit/reference/uiview_class/uiview/uiview.html

Answer 4

Shouldn't you be using the following to remove the view from its superview?

[vc.view removeFromSuperview];