Mr.Peng解决XCode6 iOS7控制器View整体上移问题

在项目中，在适配iOS7时，遇到了下面的问题，请看下图：


控制器的内容整体上移了大概44像素。而44像素对iOS开发人员来说，肯定比较敏感。而且能够发现navigationBar是透明的，猜测：可能是导航栏透明的问题。动手试一试。在controller中的-(void）viewDidLoad中加入

self.navigationController.navigationBar.translucent = NO;

现在⌘+R运行下。结果如下图：

综上所述：猜想正确。

现在Google一下为什么呢？

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回归正题。在StockOverflow上面也有人在问相同问题。传送门:
https://developer.apple.com/library/prerelease/ios/documentation/UserExperience/Conceptual/TransitionGuide/AppearanceCustomization.html#//apple_ref/doc/uid/TP40013174-CH15-SW1
这个人自问自答了，而自答的答案也是设置navigationBar的translucent = NO。最下面有一个更好的解决方案，就是在-(void）viewDidLoad中加入

if ([self respondsToSelector:@selector(edgesForExtendedLayout)])
       self.edgesForExtendedLayout = UIRectEdgeNone;

来解决此问题。我试了两种方法之后，感觉都是达到同样的目的，但是我还是觉得第二种为最佳解决方法，之所以我认为是最好的解决，是因为`apple doc,明确说明了此情况。

iOS 7 brings several changes to how you layout and customize the appearance of your UI. The changes in view-controller layout, tint color, and font affect all the UIKit objects in your app. In addition, enhancements to gesture recognizer APIs give you finer grained control over gesture interactions.

Using View Controllers

In iOS 7, view controllers use full-screen layout. At the same time, iOS 7 gives you more granular control over the way a view controller lays out its views. In particular, the concept of full-screen layout has been refined to let a view controller specify the layout of each edge of its view.

The wantsFullScreenLayout view controller property is deprecated in iOS 7. If you currently specify wantsFullScreenLayout = NO, the view controller may display its content at an unexpected screen location when it runs in iOS 7.

To adjust how a view controller lays out its views, UIViewController provides the following properties:

• edgesForExtendedLayout

The edgesForExtendedLayout property uses the UIRectEdge type, which specifies each of a rectangle’s four edges, in addition to specifying none and all. Use edgesForExtendedLayout to specify which edges of a view should be extended, regardless of bar translucency. By default, the value of this property is UIRectEdgeAll.

• extendedLayoutIncludesOpaqueBars

If your design uses opaque bars, refine edgesForExtendedLayout by also setting the extendedLayoutIncludesOpaqueBars property to NO. (The default value of extendedLayoutIncludesOpaqueBars is NO.)

• automaticallyAdjustsScrollViewInsets

If you don’t want a scroll view’s content insets to be automatically adjusted, set automaticallyAdjustsScrollViewInsets to NO. (The default value of automaticallyAdjustsScrollViewInsets is YES.)

• topLayoutGuide, bottomLayoutGuide

The topLayoutGuide and bottomLayoutGuide properties indicate the location of the top or bottom bar edges in a view controller’s view. If bars should overlap the top or bottom of a view, you can use Interface Builder to position the view relative to the bar by creating constraints to the bottom of topLayoutGuide or to the top of bottomLayoutGuide. (If no bars should overlap the view, the bottom of topLayoutGuide is the same as the top of the view and the top of bottomLayoutGuide is the same as the bottom of the view.) Both properties are lazily created when requested.

我自己的理解：在iOS7中视图控制器都使用了full-screen layout(全屏布局)，而且全屏布局细化到了每个边缘的布局。而wantsFullScreenLayout在iOS7中废弃了。不过可以用edgesForExtendedLayout、extendedLayoutIncludesOpaqueBars、automaticallyAdjustsScrollViewInsets、topLayoutGuide，bottomLayoutGuide这几个属性来适配控制器的布局。