UIAlertView / UIAlertController兼容iOS 7和iOS 8 [英] UIAlertView/UIAlertController iOS 7 and iOS 8 compatibility

问题描述

我正在使用Swift编写应用程序，我需要显示警报。该应用必须兼容iOS 7和iOS 8。由于 UIAlertView 已替换为 UIAlertController ，如何检查 UIAlertController 可用而不检查系统版本？我听说Apple建议我们不要检查设备的系统版本，以确定API的可用性。

I am using Swift to write an app and I need to show an alert. The app must be iOS 7 and iOS 8 compatible. Since UIAlertView has been replaced with UIAlertController, how can I check if the UIAlertController is available without checking the system version? I have been hearing that Apple recommends that we should not check the system version of the device in order to determine the availability of an API.

这就是我用来做的iOS 8但在iOS 7上崩溃， dyld：未找到符号：_OBJC_CLASS _ $ _ UIAlertAction ：

This is what I am using for iOS 8 but this crashes on iOS 7 with "dyld: Symbol not found: _OBJC_CLASS_$_UIAlertAction" :

let alert = UIAlertController(title: "Error", message: message, preferredStyle: .Alert)
let cancelAction = UIAlertAction(title: "OK", style: .Cancel, handler: nil)
alert.addAction(cancelAction)
presentViewController(alert, animated: true, completion: nil)

如果我使用UIAlertView for iOS 8，我收到此警告：警告：尝试从视图控制器中解除< _UIAlertShimPresentingViewController：0x7bf72d60>正在进行演示或解雇！

If I use the UIAlertView for iOS 8, I get this warning: Warning: Attempt to dismiss from view controller <_UIAlertShimPresentingViewController: 0x7bf72d60> while a presentation or dismiss is in progress!

推荐答案

检测模式与目标相同C风格。

The detection pattern is identical to the Objective-C style.

您需要检测当前活动运行时是否能够实例化此类

You need to detect whether the current active runtime has the ability to instantiate this class

if objc_getClass("UIAlertController") != nil {

     println("UIAlertController can be instantiated")

      //make and use a UIAlertController

 }
 else {

      println("UIAlertController can NOT be instantiated")

      //make and use a UIAlertView
}

请勿尝试根据操作系统版本计算出来。您需要检测不操作系统的能力。

Don't try and work out this based on the OS version. You need to detect abilities NOT OS.

编辑

此答案的原始检测器 NSClassFromString（UIAlertController）在 -O 优化下失败，因此已更改当前版本适用于发布版本

The original detector for this answer NSClassFromString("UIAlertController") fails under -O optimisation so its been changed to the current version which does work for Release builds

编辑2

NSClassFromString 正在Xcode 6.3 / Swift 1.2的所有优化中工作

NSClassFromString is working at all optimisations in Xcode 6.3/Swift 1.2

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