viewWillAppear: not being called inside a UINavigationController

最新推荐文章于 2018-05-03 16:00:20 发布

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最新推荐文章于 2018-05-03 16:00:20 发布

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分类专栏： iOS 文章标签： uinavigationcontroller refactoring hierarchy methods testing tree

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本文介绍了一个关于 UINavigationController 作为 UIViewController 子视图时出现的数据不刷新问题。作者通过调整视图层级并进行重构后发现，在导航控制器中切换视图时未能正确调用 viewWillAppear 方法，导致视图未能更新。文中提供了如何手动调用该方法以解决问题的具体实现。

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I just stumbled on a small problem that gave me a great headache. I changed the view hierarchy to implement flipping preferences on the back of my App’s main view. Accordingly, I had to move some stuff out of the nibs and into the code. Iin other words, some heavy refactoring, and without testing (I know, bad bad me).

So basically I now have a root UIViewController which has a UINavigationController as a subview; this, in turn, loads a number of UIViewControllers to navigate my items hierarchy.

Today, while working on cosmestic/usability improvements, I realised that something was definitely not working. When moving back and forth in my items, data were not refreshed. This pointed to one culprit, viewWillAppear not being called in the UIViewControllers.

After some googling I found out that if you add a UINavigationController as a subview of a UIViewController subclass, you must explicitly call its viewWillAppear method from its container; otherwise, they won’t be called, and when moving back and forth in the navigation tree, your UIViewControllers’ viewWillAppear: methods won’t be called.

It’s quite simple; assuming that projectNavigationController is a navigation controller added as a a subview of this UIViewController subclass, just make sure you add this simple call:

-(void)viewWillAppear:(BOOL)animated { 
	[super viewWillAppear:animated];
	[projectNavigationController viewWillAppear:animated];
}

Of course the same applies to your other viewWill/Did methods

-(void)viewWillDisappear:(BOOL)animated { 
	[super viewWillDisappear:animated];
	[projectNavigationController viewWillDisappear:animated];
}
-(void)viewDidAppear:(BOOL)animated { 
	[super viewDidAppear:animated];
	[projectNavigationController viewDidAppear:animated];
}
-(void)viewDidDisappear:(BOOL)animated { 
	[super viewDidDisappear:animated];
	[projectNavigationController viewDidDisappear:animated];
}