我有这个问题。我不小心把这个删了

xmlns:tools="http://schemas.android.com/tools"

在我的XML文件和Java文件中，这开始导致整个项目的构建错误。当我重新输入我删除的内容时，它又工作了:)

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.

在我的情况下，我检查了所有以前的解决方案，但没有生成r。我只是从菜单文件夹中删除了我的main.xml文件，并重新生成它。我不知道为什么，但它现在对我有用……

确保你没有导入

android.R;

同样会导致这种情况的是，如果你有一个scale9可绘制文件与另一个文件具有相同的名称:

img_file.9.png img_file.png

只需删除其中一个文件就可以修复它。

我遇到过几次这样的问题。我发现，如果我没有通过应用程序的名称导入包R，例如，如果我的应用程序有包名称示例。然后我发现我必须导入example.test.R才能访问任何资源。

如果没有导入，那么返回的资源是默认资源，不包括我自己的资源。

也就是说，如果你发现你只是得到一个默认资源的列表，然后检查，以确保你导入application_package_name。R而不是android。