How come some of my UIViews are shifted after navi

问题:

In some of my application designs or for just some UIViews, following a navigationController's pushViewController, my new view will be shifted off the window by the height of the status bar. As a result, I will put this code stub in the viewDidLoad method.

CGRect  frameAt = [self.view frame];
CGRect  statusBarFrame = [[UIApplication sharedApplication] statusBarFrame];
frameAt.origin.y += statusBarFrame.size.height;
[self.view setFrame: frameAt];

It does not make sense to me that this is the intention of XCode and Interface Builder, so I suspect that I am doing something fundamentally wrong with the SDK during my view design. Furthermore, on the rare occasion that I don't have to shift my view, I really don't know what the difference in the two design approaches.

Note also, that most of the time I try to design my views using IB, with some minor customization.

Does anyone else run into this and know what they do to fix without such a code stub?

回答1:

I've used Apple's NavBar sample code to try and reproduce this problem.

the applicationDidFinishLaunching is originally implemented like this:

[window addSubview:navigationController.view];
[window makeKeyAndVisible];

If I change it to this:

UIViewController *shellController = [[UIViewController alloc] initWithNibName:nil bundle:nil];
[shellController.view addSubview:navigationController.view];
[window addSubview:shellController.view];
[window makeKeyAndVisible];

Then I get the gap appearing.

However if I only do this:

UIView *shell = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
[shell addSubview:navigationController.view];
[window addSubview:shell];
[window makeKeyAndVisible];

Then everything looks normal.

So I guess every view controller will offset its view if its the root view controller. But the navigation controller overrides this behaviour to offset its view regardless of whether it's the root view controller. Therefore I would say your gap is appearing because you've got a navigation controller somewhere lower in the hierarchy than it's supposed to be.

回答2:

The main thing to keep in mind here is that a view controller will set the frame of its view itself. This is because the amount of space available to the view may change during the lifetime of the app, and only the view controller knows how to adjust the view's frame appropriately. Examples of when the amount of space changes include the navigation bar changing height, turning the device from portrait to landscape and the status bar can also increase in height if the user is taking a call. Because of this you should not modify the view's frame yourself.

So, the first thing you need to is is remove all code related to modifiying the view's frame.

Now you need to design your views with the mindset that the frame size could change at any moment. This means setting the autoresizing property of each subview properly. If you do this, then it won't matter if you turn on the simulated navigation and status bars or not; they're just there to help you see what the final result will look like in most cases.

You can set the autoresizing property of each subview in Interface Builder in the Size Inspector (the one with the ruler icon). In the animation, the white box represents the root view of the view controller, the red box represents the currently selected subview. You'll notice that the subview is anchored to the top-left corner of the root view by default. This is fine if the size of the view never changes, but we know that not to be true. If you have subviews that you want to appear at the bottom no-matter-what, then you need to play with the diagram to the left. The way it works is if one of the four lines around the edge is selected, then the distance between that edge of the root view and the edge of the subview is fixed. So if you want a subview to appear at the bottom, you need to make sure the bottom-most line is selected and not the top. The two lines in the middle affect whether the size of the subview changes when the root view change size. So, for example, if you had a table view that you wanted to occupy the entire height of the screen, you would make sure the inner vertical line was selected. This is called the struts and springs model.

If you are adding subviews programatically you need to set the autoresizingMask property on each subview. Here's an explanation.

Hope that helps!

回答3:

I've run into similar issues. Check out my two previous questions:

IPhone - After dismissing Modal View Controller - gap is left at top of page

IPhone - UIView addSubview Gap at top

回答4:

link text

A similar bug is discussed here.

Also is animation set to NO? Try setting it to YES as this solved a similar problem I was facing.

回答5:

Moshy's answer was very helpful as I finally realized the meaning of the dotted/solid lines in IB for controlling the resize properties of UIView elements.

However, adjusting those properties did not address a similar problem I faced with one of my views. This view had a status and top bar defined in IB. It was a slightly heavy one, containing a UIWebView that would load a HTML string within viewWillAppear and a few other interface elements.

While loading the view, if the user suddenly changed the orientation of the device from portrait to landscape, all contents of the view would shift downwards by the height of the status bar. The resulting gap between the view controls and its top would remain even after switching back to portrait orientation.

What finally solved my issues, and my remaining hair, was adding the line:

    self.view.frame = [[UIScreen mainScreen] bounds];

within

-(void) willAnimateRotationToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration

Ever since my view contents are held in place despite abrupt device orientation changes.