UINavigationController: Apply Common Padding/Margin to all Popped View Controller's Views - cocoa-touch

Question

I have a UINavigationController and I would like the view of every view controller that is popped onto the stack to have a common padding/margin (e.g. 25 pixels on all sides). What is the best way to accomplish this?
I originally thought that I could implement UINavigationControllerDelegate and inside the navigationController:didShowViewController:animated or navigationController:willShowViewController:animated methods, simply change the frame of the view controller that was about to be displayed. This does not seem to have an effect though.
I tried to do the same thing inside the view controller's viewDidAppear and viewWillAppear methods, but this also did not work. Ideally, I don't want to put any logic in the controllers anyway, as they may not always be used inside a navigation controller.
One last idea that I haven't tried yet is to create a "wrapper" UIViewController that would actually get pushed onto this stack. This wrapper would add the real view controller's view as a subview with a frame that would provide the desired margin. The downside here is that I would need to subclass UINavigationController and override pushViewController:animated, where the wrapper would be initialized and pushed. Apple's documentation indicates that UINavigationController is not meant to be subclassed.
Thanks in advance.

Answer 1

I solved this by putting a "wrapper" UIView around the UIViewController's view instead of the UIViewController itself. The wrapper view then pads the subview by setting the subview's frame in the layoutSubviews method.
I've attached the code I used for convenience. To use, replace your UINavigationController with the PaddedNavigationController, and set the PaddedNavigationController's insets property.
PaddedNavigationController.h:
#import <Foundation/Foundation.h>
#interface PaddedNavigationController : UINavigationController
{
UIEdgeInsets _insets;
}
#property (nonatomic, assign) UIEdgeInsets insets;
#end
PaddedNavigationController.m:
#import "PaddedNavigationController.h"
#interface PaddedView : UIView
{
UIView *_view;
UIEdgeInsets _insets;
}
#property (nonatomic, assign) UIEdgeInsets insets;
+ (PaddedView *) wrapView:(UIView *)view withInsets:(UIEdgeInsets)insets;
- (id) initWithView:(UIView *)view insets:(UIEdgeInsets)insets;
#end
#implementation PaddedNavigationController
#synthesize insets = _insets;
- (void) pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
//check if the UIViewController's view has already been wrapped by the PaddedView; don't want to wrap it twice
if(![viewController.view isKindOfClass:[PaddedView class]])
{
viewController.view = [PaddedView wrapView:viewController.view withInsets:self.insets];
}
[super pushViewController:viewController animated:animated];
}
- (void) setInsets:(UIEdgeInsets)insets
{
_insets = insets;
//loop through this navigation controller's view controllers and set the new insets on any PaddedViews
for(UIViewController *viewController in self.viewControllers)
{
if([viewController.view isKindOfClass:[PaddedView class]])
{
PaddedView *padded = (PaddedView *)viewController.view;
padded.insets = insets;
}
}
}
#end
#implementation PaddedView
#synthesize insets = _insets;
+ (PaddedView *) wrapView:(UIView *)view withInsets:(UIEdgeInsets)insets
{
return [[[PaddedView alloc] initWithView:view insets:insets] autorelease];
}
- (id) initWithView:(UIView *)view insets:(UIEdgeInsets)insets
{
if(self = [super initWithFrame:view.frame])
{
_insets = insets;
self.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
_view = [view retain];
[self addSubview:view];
}
return self;
}
- (void) dealloc
{
[_view release];
[super dealloc];
}
- (void) layoutSubviews
{
//apply the insets to the subview
_view.frame = CGRectMake(self.insets.left, self.insets.top, self.frame.size.width - self.insets.left - self.insets.right, self.frame.size.height - self.insets.top - self.insets.bottom);
}
- (void) setInsets:(UIEdgeInsets)insets
{
_insets = insets;
//we need to re-layout the subviews as the insets have changed
[self layoutSubviews];
}
#end