我发现这发生在我与一个破碎的布局和一切爆炸。放松，这就像你第一次学习编程时犯的错误一样，你忘记了一个分号，它就会产生100个错误。许多人惊慌失措，按下所有的按钮，使事情变得更糟。

解决方案

Make sure that anything the R. links to is not broken. Fix all errors in your XML files. If anything in the ADKs are broken, R will not regenerate. If you somehow hit something and created import android.R in your activity, remove it. Run Project -> Clean. This will delete and regenerate R and BuildConfig. Make sure Project -> Build Automatically is ticked. If not, build it manually via Menu -> Project -> Build Project . Wait a few seconds for the errors to disappear. If it doesn't work, delete everything inside the /gen/ folder If it still doesn't work, try right-clicking your project -> Android Tools -> Fix Project Properties. Check your *.properties files (in the root folder of your app folder) and make sure that the links in there are not broken. Right-click your project > properties > Android. Look at the Project Build Target and Library sections on the right side of the page. Your Build Target should match the target in your AndroidManifest.xml. So if it's set to target 17 in AndroidManifest, make sure that the Target Name is Android 4.2. If your Library has an X under the reference, remove and re-add the library until there's a green tick. This might happen if you've moved a few files and folders around.

如果R不能再生怎么办

这通常发生在XML文件损坏时。

Check errors inside your XML files, mainly within the /res/ folder Common places are /layout/ and /values/, especially if you've changed one of them recently Check AndroidManifest.xml. I find that often I change a string and forget to change the string name from AndroidManifest.xml. Check that Android SDK Build-tools is installed. Window -> Android SDK Manager -> Tools -> Android SDK Build-tools Make sure when you update the Android SDK Tools, you also update the Android SDK Platform-tools and Android ADK Build-tools. Build fails silently if they don't match. If you can't find the issue, right click /gen/ -> Restore from local history... -> tick R.java -> click Restore. Even if it doesn't solve the problem, it will clear out the extra errors to make the problem easier to find.

主要是R.java文件与.xml文件和Java。我们知道XML标记，但是Java呢?因此，我们需要有一个唯一的id来标识标记。

这里的R.java文件主要与使用Java获取值的XML文件相关。

在阅读了许多帖子和YouTube视频后，我发现我们每个人都因为不同的原因丢失了R.java。

下面是我在Eclipse中修复这个问题的方法:

在gen文件夹中手动创建R.java并保存。 然后进入项目，点击“清洁”

将显示以下消息，您的文件将被自动重写:

手动修改了R.java !恢复到生成版本!

我在AndroidManifest.xml文件中有一个错误，所以在修复这个错误后，点击

运行- >清洁

它产生了R.java

不要从strings.xml中删除这两行:

android:icon="@drawable/icon" android:label="@string/app_name"

android:name=".HelloAutoComplete"

android:label="@string/app_name"

我发现了一个解决方案，为什么R.class不被Eclipse重新创建后- 2清洁，构建等。

问题在strings.xml中:

<string name="hello">Hello World, HelloAutoComplete!</string>

<string name="app_name">HelloAutoComplete</string>

这些是Eclipse在创建项目时默认创建的。

当然，您需要根据自己的需求更改strings.xml。有时你会清除字符串。xml这两行代码:

它在AndroidManifest.xml文件中产生了一个问题:

<application android:icon="@drawable/icon"  android:label="@string/app_name">
<activity android:name=".HelloAutoComplete" android:label="@string/app_name">

所以它不能与strings。xml通信。