IOS7 APP 升级的10个TIP 建议

1. There is no way to preserve the iOS 6 style status bar layout. The status bar will always overlap your application on iOS 7

2. Do not confuse status bar appearance with status bar layout. The appearance (light or default) does not affect how the status bar is laid out (frame/height/overlap). It is important to note as well that the system status bar no longer has any background color. When the API refers to UIStatusBarStyleLightContent, they mean white text on a clear background. UIStatusBarStyleDefault is black text on a clear background.

3. Status bar appearance is controlled along one of two mutually-exclusive basis paths: you can either set them programmatically in the traditional manner, or UIKit will update the appearance for you based on some new properties of UIViewController. The latter option is on by default. Check your app’s plist value for “ViewController-Based Status Bar Appearance” to see which one you’re using. If you set this value to YES, every top-level view controller in your app (other than a standard UIKit container view controller) needs to override preferredStatusBarStyle, returning either the default or the light style. If you edit the plist value to NO, then you can manage the status bar appearance using the familiar UIApplication methods.

4. UINavigationController will alter the height of its UINavigationBar to either 44 points or 64 points, depending on a rather strange and undocumented set of constraints. If the UINavigationController detects that the top of its view’s frame is visually contiguous with its UIWindow’s top, then it draws its navigation bar with a height of 64 points. If its view’s top is not contiguous with the UIWindow’s top (even if off by only one point), then it draws its navigation bar in the “traditional” way with a height of 44 points. This logic is performed by UINavigationController even if it is several children down inside the view controller hierarchy of your application. There is no way to prevent this behavior.

5. If you supply a custom navigation bar background image that is only 44 points (88 pixels) tall, and the UINavigationController’s view’s bounds matches the UIWindow’s bounds (as discussed in #4), the UINavigationController will draw your image in the frame (0,20,320,44), leaving 20 points of opaque black space above your custom image. This may confuse you into thinking you are a clever developer who bypassed rule #1, but you are mistaken. The navigation bar is still 64 points tall. Embedding a UINavigationController in a slide-to-reveal style view hierarchy makes this abundantly clear.

6. Beware of the confusingly-named edgesForExtendedLayout property of UIViewController. Adjusting edgesForExtendedLayout does nothing in most cases. The only way UIKit uses this property is if you add a view controller to a UINavigationController, then the UINavigationController uses edgesForExtendedLayout to determine whether or not its child view controller should be visible underneath the navigation bar / status bar area. Setting edgesForExtendedLayout on the UINavigationController itself does nothing to alter whether or not the UINavigationController has a 44 or 64 point high navigation bar area. See #4 for that logic. Similar layout logic applies to the bottom of your view when using a toolbar or UITabBarController.

7. If all you are trying to do is prevent your custom child view controller from underlapping the navigation bar when inside a UINavigationController, then set edgesForExtendedLayout to UIRectEdgeNone (or at least a mask that excludes UIRectEdgeTop). Set this value as early as possible in the life cycle of your view controller.

8. UINavigationController and UITabBarController will also try to pad the contentInsets of table views and collection views in its subview hierarchy. It does this in a manner similar to the status bar logic from #4. There is a programmatic way of preventing this, by setting automaticallyAdjustsScrollViewInsets to NO for your table views and collection views (it defaults to YES). This posed some serious problems for Whisper and Riposte, since we use contentInset adjustments to control the layout of table views in response to toolbar and keyboard movements.

9. To reiterate: there is no way to return to iOS 6 style status bar layout logic. In order to approximate this, you have to move all the view controllers of your app into a container view that is offset by 20 points from the top of the screen, leaving an intentionally black view behind the status bar to simulate the old appearance. This is the method we ended up using in Riposte and Whisper.

10. Apple is pushing very hard to ensure that you don’t try to do #9. They want us to redesign all our apps to underlap the status bar. There are many cogent arguments, however, for both user experience and technical reasons, why this is not always a good idea. You should do what is best for your users and not simply follow the whimsy of the platform.