最近做了iOS 9的适配，程序出现大量警告也做了些处理，写出来分先给大家。
一、iOS 9适配
问题一：
<Error>: CGContextSaveGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
出错原因：设置app的状态栏样式的使用使用了旧的方式，在info.plist里面设置了View controller-based status bar appearance为NO，默认为YES，一般式iOS6的时候使用这种方式，iOS7，8也兼容，但是到了iOS9就报了警告。以前我们使用代码为[[UIApplication sharedApplication]setStatusBarStyle:UIStatusBarStyleLightContent];以前我们通过上面代码改变状态了颜色
解决办法：：
1.删除 原先的设置代码[[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleLightContent];
2.修改方式将View controller-based status bar appearance设置为YES，然后使用新的方式来实现状态栏的样式。
3.如果你是用UINavigationController只需要在appdelegate里面添加 [[UINavigationBar appearance] setBarStyle:UIBarStyleBlack]就行。
问题二：
-canOpenURL: failed for URL: "weixin://app/wx9c8771d3c07dfd30/" - error: "This app is not allowed to query for scheme weixin"
解决办法：
info.plist加入
<key>LSApplicationQueriesSchemes</key>
<array>
<string>urlscheme1</string>
<string>urlscheme2</string>
<string>urlscheme3</string>
<string>urlscheme4</string>
</array>
问题三：
Bitcode问题
原因：Xcode7 及以上版本会默认开启 bitcode 。。
解决方法：
1.更新library使包含Bitcode，否则会出现以上的警告。
2.关闭Bitcode，Build Settings”->”Enable Bitcode”改成"NO"
问题四：
App Transport Security has blocked a cleartext HTTP (http://) resource load since it is insecure. Temporary exceptions can be configured via your app‘s Info.plist file.
在iOS9中，将原http协议改成了https协议，使用 TLS1.2 SSL加密请求数据。
解决方法：
在info.plist 加入key
<key>NSAppTransportSecurity</key> <dict> <key>NSAllowsArbitraryLoads</key> <true/> </dict>
参考资料:
二、消除warning
warning 1：
warning :no rule to process file ’…/BBCommmunityVerify.h’ of type sourcecode.c.h for architecture arm64
解决办法：
可以看出是某个.h文件出了问题，在Build Phases -> Compile Sources 里面删除该文件即可
warning 2：
warning：Automatic Preferred Max Layout Width before iOS 8.0
出现条件：
the warning will appear if
(1) you‘re using auto layout,
(2) "Automatic" is set for a multiline label [you can check this in the size inspector for the label], and
(3) your deployment target < iOS 8.
上面的意思是警告出现的三个条件
1.使用自动布局
2.label多行且设置为.Automatic
3.版本低于iOS 8.
解决办法：
1 - (void)layoutSubviews {
2 [super layoutSubviews];
3 CGFloat availableLabelWidth = self.label.frame.size.width; self.label.preferredMaxLayoutWidth = availableLabelWidth;
4 [super layoutSubviews];
5 }
The first call to [super layoutSubviews] will evaluate the constraints on the label (since it’s a direct subview) and change its frame accordingly. At this point the width is useful, but the height is not; the height was set using the label’s intrinsic content size, which in turn relied on a preferred max layout width value that is now stale.
Now we know the actual width of the label, we set that as its max layout width. Internally, this causes the label to invalidate its intrinsic content size; when it’s next queried, it will have the accurate height for its current width. With all layout information in place, we call[super layoutSubviews] again.
大概意思是第一个[super layoutSubviews]; 获得width,然后设置self.label.preferredMaxLayoutWidth，第二个用来计算行数。
warning 3:
directory not found for option ‘-F/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator9.0.sdk/Developer/Library/Frameworks‘
去掉警告的办法如下：
1选择工程, 编译的 (targets)
2选择 Build Settings 菜单
3查找 Library Search Paths 和 Framework Search Paths，-L 找Library Search Paths，-F找Framework Search Paths 删掉编译报warning的路径即OK
参考链接：http://stackoverflow.com/questions/32630967/warning-when-i-update-to-xcode-7/32658881#32658881
warning 4:
warning: Plain Style unsupported in a Navigation Item
解决办法：
1.找到文件,open as source code 搜索 style=“plain"
2.修改<barButtonItem key="rightBarButtonItem" style="plain" id="juB-DL-F9i">
为<barButtonItem key="rightBarButtonItem" id="juB-DL-F9i">
也就是删除style=“plain"
warning 5：
warning:Scene is unreachable due to lack of entry points and does not have an identifier for runtime access via -instantiateViewControllerWithIdentifier:
错误原因： storyboard中存在无法获得的控制器。既不是initial控制器，也没有idenifier;
解决办法：没用就删除，有用的话添加identifier;
warning 6:
warning:Frame for “Phone Text Filed” will be different at run time
这个简单，布局报黄，更新布局即可，可设置快捷键。。。