TableView

當tableview的style為grouped的時候，會出現每個section之間有間距。

官方解析：Link on iOS 11, all estimated heights default to UITableViewAutomaticDimension Headers, footers, and cells use self-sizing by default.

- 解決方案：

如果開發者不想用這個新特性，可以在代理方法裏面設置具體的高度，然後設置

tableView.estimatedRowHeight = 0 
tableView.estimatedSectionHeaderHeight
 
 = 0 
tableView.estimatedSectionFooterHeight = 0

TitleView

因為iOS11 的navbar的大標題和搜索欄的新特性，navbar的子視圖發生了變化。 如果沒有給出明確的長寬，就會出現Zero-size的出現，就是說titleview不見了，或者各種奇怪的事情出現。

- 解決方案：

1. 給出指定的長寬，和子view設置好對應的約束。
2. 或者重寫intrinsicContentSize方法，設置成UILayoutFittingExpandedSize,讓它自己自動擴展。

@available(iOS 6.0, *)
public let UIViewNoIntrinsicMetric
 
: CGFloat

// Size To Fit

@available(iOS 6.0, *)
public let UILayoutFittingCompressedSize: CGSize
@available(iOS 6.0, *)
public let UILayoutFittingExpandedSize: CGSize

如果設置成擴展的話titleView和兩邊的item粘在一起了，所以需要做一下子視圖的布局。

題外話： iOS6有一個API，systemLayoutSizeFitting，可以根據view的約束計算出對應的大小，具體可以看API文檔。

Safe Area

這個主要影響用到mj的列表頁面，和隱藏navbar的列表頁面。

Safe Area是系統自己算的，系統會根據state bar的高度，navbar、tabbar是否透明(isTranslucent)。

每個view都有一個叫safeAreaInsets的屬性（get only）。 如果開發者需要更改view的safe area 可以在controller設置additionalSafeAreaInsets去屬性去弄。

例如：

帶有navbar，和tabbar的頁面。

controller.view.safeAreaInsets 為 UIEdgeInsets(top: 64.0, left: 0.0, bottom: 49.0, right: 0.0)

如果想改為（20，0，49，0）只需要做如下操作。

controller.view.additionalSafeAreaInsets = UIEdgeInsets(top: -44.0, left: 0.0, bottom: -49.0, right: 0.0)

其實無論設置成（-20000，0，0，0）也是最終得到的（20，0，49，0）,還有就是無論設置bottom為-49還是其他的值，都無法抵消tabbar的高度，也就是說系統不允許我們去縮減bottom的值，可能是因為iPhoneX的底部虛擬home鍵。

view.safeAreaInsets是影響其子ScrollView的adjustedContentInset。 ScrollView會根據contentInsetAdjustmentBehavior屬性去設置 adjustedContentInset。

public enum UIScrollViewContentInsetAdjustmentBehavior : Int {
    case automatic // Similar to .scrollableAxes, but for backward compatibility will also adjust the top & bottom contentInset when the scroll view is owned by a view controller with automaticallyAdjustsScrollViewInsets = YES inside a navigation controller, regardless of whether the scroll view is scrollable

    case scrollableAxes // Edges for scrollable axes are adjusted (i.e., contentSize.width/height > frame.size.width/height or alwaysBounceHorizontal/Vertical = YES)

    case never // contentInset is not adjusted

    case always // contentInset is always adjusted by the scroll view‘s safeAreaInsets
}

1. UIScrollViewContentInsetAdjustmentAutomatic：如果scrollview在一個automaticallyAdjustsScrollViewContentInset = YES的controller上，並且這個Controller包含在一個navigation controller中，這種情況下會設置在top & bottom上 adjustedContentInset = safeAreaInset + contentInset不管是否滾動。其他情況下與UIScrollViewContentInsetAdjustmentScrollableAxes相同
2. UIScrollViewContentInsetAdjustmentScrollableAxes: 在可滾動方向上adjustedContentInset = safeAreaInset + contentInset，在不可滾動方向上adjustedContentInset = contentInset；依賴於scrollEnabled和alwaysBounceHorizontal / vertical = YES，scrollEnabled默認為yes，所以大多數情況下，計算方式還是adjustedContentInset = safeAreaInset + contentInset
3. UIScrollViewContentInsetAdjustmentNever: adjustedContentInset = contentInset
4. UIScrollViewContentInsetAdjustmentAlways: adjustedContentInset = safeAreaInset + contentInset

- 使用MJ的列表頁的適配方案

if #available(iOS 11, *) {
    t.contentInset.top += kTopBarHeight
    t.contentInset.bottom += kHomeBarHeight // 如果列表底部沒有任何toolbar的需要添加，為了適配iPhone X
    t.contentInsetAdjustmentBehavior = .never
}

底層API命名改變

例如我使用一些第三方庫的時候，它們有用到一些API如check_compile_time（） 在iOS11裏面的命名改變為__Check_Compile_Time（）。

-解決方案：

找到對應的頭文件，搜索舊的API一般都有說明的。

/*
 *	For time immemorial, Mac OS X has defined version of most of these macros without the __ prefix, which
 *	could collide with similarly named functions or macros in user code, including new functionality in
 *	Boost and the C++ standard library.
 *
 *  macOS High Sierra and iOS 11 will now require that clients move to the new macros as defined above.
 *
 *  If you would like to enable the macros for use within your own project, you can define the
 *  __ASSERT_MACROS_DEFINE_VERSIONS_WITHOUT_UNDERSCORES macro via an Xcode Build Configuration.
 *  See "Add a build configuration (xcconfig) file" in Xcode Help. 
 *
 *  To aid users of these macros in converting their sources, the following tops script will convert usages
 *  of the old macros into the new equivalents.  To do so, in Terminal go into the directory containing the
 *  sources to be converted and run this command.
 *
    find . -name ‘*.[c|cc|cp|cpp|m|mm|h]‘ -print0 |  xargs -0 tops -verbose \
      replace "check(<b args>)" with "__Check(<args>)"       replace "check_noerr(<b args>)" with "__Check_noErr(<args>)"       replace "check_noerr_string(<b args>)" with "__Check_noErr_String(<args>)"       replace "check_string(<b args>)" with "__Check_String(<args>)"       replace "require(<b args>)" with "__Require(<args>)"       replace "require_action(<b args>)" with "__Require_Action(<args>)"       replace "require_action_string(<b args>)" with "__Require_Action_String(<args>)"       replace "require_noerr(<b args>)" with "__Require_noErr(<args>)"       replace "require_noerr_action(<b args>)" with "__Require_noErr_Action(<args>)"       replace "require_noerr_action_string(<b args>)" with "__Require_noErr_Action_String(<args>)"       replace "require_noerr_string(<b args>)" with "__Require_noErr_String(<args>)"       replace "require_string(<b args>)" with "__Require_String(<args>)"       replace "verify(<b args>)" with "__Verify(<args>)"       replace "verify_action(<b args>)" with "__Verify_Action(<args>)"       replace "verify_noerr(<b args>)" with "__Verify_noErr(<args>)"       replace "verify_noerr_action(<b args>)" with "__Verify_noErr_Action(<args>)"       replace "verify_noerr_string(<b args>)" with "__Verify_noErr_String(<args>)"       replace "verify_string(<b args>)" with "__Verify_String(<args>)"       replace "ncheck(<b args>)" with "__nCheck(<args>)"       replace "ncheck_string(<b args>)" with "__nCheck_String(<args>)"       replace "nrequire(<b args>)" with "__nRequire(<args>)"       replace "nrequire_action(<b args>)" with "__nRequire_Action(<args>)"       replace "nrequire_action_quiet(<b args>)" with "__nRequire_Action_Quiet(<args>)"       replace "nrequire_action_string(<b args>)" with "__nRequire_Action_String(<args>)"       replace "nrequire_quiet(<b args>)" with "__nRequire_Quiet(<args>)"       replace "nrequire_string(<b args>)" with "__nRequire_String(<args>)"       replace "nverify(<b args>)" with "__nVerify(<args>)"       replace "nverify_string(<b args>)" with "__nVerify_String(<args>)"       replace "require_action_quiet(<b args>)" with "__Require_Action_Quiet(<args>)"       replace "require_noerr_action_quiet(<b args>)" with "__Require_noErr_Action_Quiet(<args>)"       replace "require_noerr_quiet(<b args>)" with "__Require_noErr_Quiet(<args>)"       replace "require_quiet(<b args>)" with "__Require_Quiet(<args>)"       replace "check_compile_time(<b args>)" with "__Check_Compile_Time(<args>)"       replace "debug_string(<b args>)" with "__Debug_String(<args>)"
 *
 */

參考文章

官方適配iOS11原文
譯文

safe area

為App適配iOS11