iOS 滚动视图内容自动偏移总结

[iOS7 , iOS11):
viewcontroller参数automaticallyAdjustsScrollViewInsets决定其中scrollview偏移量参数contentInset：

默认情况下：automaticallyAdjustsScrollViewInsets = YES，contentInset = {64,0,0,0}，tabbarcontroller情况下为{64,0,49,0}，很容易理解假设设置scorllview的frame为屏幕大小，其可控高度为其高度减掉导航条的64和tabbar的49

导航条隐藏时，两种情况下contentInset分别是{20,0,0,0},{20,0,49,0}，20是状态栏的高度

[iOS11,~):

viewcontroller新增所谓安全区域，带来一系列参数：SafeAreaInsets、additionalSafeAreaInsets、adjustedContentInset、contentInsetAdjustmentBehavior……；

原来的automaticallyAdjustsScrollViewInsets失效了，新的方案认为状态栏导航条、tabbar之间的区域为安全区域

scrollview的最终偏移量adjustedContentInset = safeAreaInset + contentInset，safeAreaInset的值与iOS 11之前的contentInset相同，iOS11中contentInset默认为{0,0,0,0}

导航条隐藏时，两种情况下safeAreaInset分别是{20,0,0,0},{20,0,49,0}，20是状态栏的高度

contentInsetAdjustmentBehavior参数：

　　UIScrollViewContentInsetAdjustmentAutomatic：如果scrollview在一个controller上，并且这个Controller包含在一个navigation controller中，这种情况下会设置在top & bottom上 adjustedContentInset = safeAreaInset + contentInset不管是否滚动。其他情况下与UIScrollViewContentInsetAdjustmentScrollableAxes相同

　　UIScrollViewContentInsetAdjustmentScrollableAxes: 在可滚动方向上adjustedContentInset = safeAreaInset + contentInset，在不可滚动方向上adjustedContentInset = contentInset；依赖于scrollEnabled和alwaysBounceHorizontal / vertical = YES，scrollEnabled默认为yes，所以大多数情况下，计算方式还是adjustedContentInset = safeAreaInset + contentInset

　　UIScrollViewContentInsetAdjustmentNever: adjustedContentInset = contentInset

　　UIScrollViewContentInsetAdjustmentAlways: adjustedContentInset = safeAreaInset + contentInset

当contentInsetAdjustmentBehavior设置为UIScrollViewContentInsetAdjustmentNever的时候，adjustContentInset值不受SafeAreaInset值的影响。

如果你想抵消这种偏移，添加additionalSafeAreaInsets参数。

 

如果你被苹果这个设计恶心到了

if (@available(iOS 11.0, *)) {
        self.table.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
    } else {
        self.automaticallyAdjustsScrollViewInsets = NO;
    }
}

另外注意：edgesForExtendedLayout和extendedLayoutIncludesOpaqueBars

这两个参数导致的view偏移问题