For most people the cause of the problem is probably mismatch between Xcode, device version and app target version. If versions are not a problem for you, most likely is that the device (iPhone/iPad) has been used with another Mac to copy apps to. This happens particularly more with a team environment where an iDevice can be used between team members. Xcode knows some other developer's Mac has connected to this device, it will show up as "Ineligible". But the previous Mac that connected to it, it will show up as normal. The quickest work around is as shown by joshstaiger among others: Go to Xcode ->Product->Destination Select the ineligible device as target. It should work.

升级XCode以确保它支持当前设备上的iOS版本。

(就我而言，我的手机使用的是iOS 9.1.x)但XCode版本是7，支持iOS 9.0设备)

我的解决方案是，我最近将iOS设备升级到8.3，但Xcode仍然无法识别。修复方法是简单地将Xcode升级到6.3:)

我的iPad是8.0，但我的部署目标设置为8.1。我在构建设置中更改了部署目标，ipad立即从“不合格”类别中移出。(我在Yosemite和XCode 6.1)

我的答案很简单，可能已经列出了，但我没有注意到:我从目标中删除了有问题的应用程序，然后启动Xcode，目标就可用了。是的，我尝试了大多数其他建议，并诉诸于从产品菜单激活目标，但这变得乏味。

随着Xcode 6.3.1的发布，首先检查更新5

验证“iOS部署目标”是<=您的设备的版本。

当你在Xcode中点击项目的目标时，你会在“Build Settings”选项卡中找到这个选项。

Then if does not work, try to restart Xcode. Sometimes we have to restart the Mac and iPhone/iPad. Take a look at the Updates below before restarting Xcode Update: in Yosemite, Xcode 6.0.1 does not support iOS 8.1, you have to update to Xcode 6.1 if you want to debug on iOS 8.1 device, or you will probably have the same problem as described in the topic Update 2: Xcode Beta 6.3 does not support iOS 8.2 (and also 8.1 - thanks @steveb). You won't see your device in deploy target list. I don't know if other versions are supported. Update 3. Use Xcode 6.2 instead of Xcode 6.3 beta in order to debug with a device running iOS 8.2 Updated 4 : for Xcode 6.3 (and eventually 6.3 beta if someone use it :) ), if you have this problem, just go to Product > Destination to select your device. Even though it says your device is ineligible, it will still allow you to select it. If your device version is >= target version, the build should work. It must be a bug for Xcode 6.3 in debug with iOS 8.3 (or maybe other iOS version) (thanks @einfach).

更新5:苹果发布了Xcode 6.3.1，修复了不合格设备的问题。如果你在Xcode 6.3中遇到这个问题，请升级到Xcode 6.3.1

发布说明(Xcode 6.3.1):

固定:设备之前被列为“不符合运行条件” 错误的被正确列出。(20121178)