In every instance in all of my classes where I reference R.id.something, the R is in red and it says "cannot resolve symbol R". Also every time there is R.layout.something it is underlined in red and says "cannot resolve method setContentView(?)". The project always builds fine. It is annoying to see this all the time. I have read many other questions on here about something similar but most involved importing projects from Eclipse. I am using what I believe to be the most recent version of Android Studio and the project was created with Android Studio and worked without any "cannot resolve R" problems. I would like to know what causes this if anyone knows.


当前回答

最近,当我更新一个项目的很多库时,我就遇到了这种情况。没有找到R,但是我可以很好地构建和运行项目。它没有崩溃。IDE只是在所有地方显示红色。

我试过

Check for damaged/improper XMLs and images, none found Check for invalid resource file names (e.g. capitalized), none found Downgrade some libraries because maybe it was a resource conflict, not resolved Lowered compileSdkVersion and targetSdkVersion because, in the past, I encountered resource issues due to this. In this project however, that was not the case. Clean, didn't help Rebuild project, didn't help Invalidate caches/Restart multiple times, didn't help Adjusted idea.max.intellisense.filesize to a very high value, didn't help Did a Lint run, no errors found

最后,我发现降级我的Gradle构建工具(从3.3.1到3.2.1)解决了这个问题。这是我唯一要做的改变。其余内容已更新。现在,我所有的库都更新了,没有问题。

buildscript {
    repositories {
        google()
        jcenter()
    }
    dependencies {
        //classpath 'com.android.tools.build:gradle:3.3.1'
        classpath 'com.android.tools.build:gradle:3.2.1'
        classpath 'com.google.gms:google-services:4.2.0'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

其他回答

建立>清洁项目

这对我很管用。同样的问题我也遇到过几次,这似乎解决了问题。除非你改变了一些东西或变量r,这个问题通常是突然发生的,当它发生在我身上时,所以我想这只是Android工作室吓坏了。哈哈

祝你过得愉快,并祝你的项目好运。

同样的问题。当我在我的可绘制文件夹中添加了一些图像并试图访问它们时开始。此外,添加的图像有大写字母的扩展名。这似乎使构建崩溃,因为即使我重命名它们,消息也是一样的,R是不可访问的。我所做的是,在.iml文件中,我寻找了excludeFolder并删除了它们(如下图所示):

  <excludeFolder url="file://$MODULE_DIR$/build/apk" />
  <excludeFolder url="file://$MODULE_DIR$/build/assets" />
  <excludeFolder url="file://$MODULE_DIR$/build/bundles" />
  <excludeFolder url="file://$MODULE_DIR$/build/classes" />
  <excludeFolder url="file://$MODULE_DIR$/build/dependency-cache" />
  <excludeFolder url="file://$MODULE_DIR$/build/incremental" />
  <excludeFolder url="file://$MODULE_DIR$/build/libs" />
  <excludeFolder url="file://$MODULE_DIR$/build/manifests" />
  <excludeFolder url="file://$MODULE_DIR$/build/res" />
  <excludeFolder url="file://$MODULE_DIR$/build/symbols" />
  <excludeFolder url="file://$MODULE_DIR$/build/tmp" />

在那之后,我重建了项目,R神奇地重新出现了。

我在androidmanifest中有android:textAllCaps = "false",这对R文件造成了严重破坏。我删除了,一切正常。我认为目标sdk设置得不够高。

以上答案都不能解决我的问题。所以我添加了我的解决方案,以防有人遇到类似的问题。在我的构建中。我有gradle依赖,

compile 'com.android.support:appcompat-v7:22+'

我的compilesdk版本是 编译esdkversion 21,所以android工作室不高兴。我简单地更新了我的compilesdkversion到23,并进行了同步。

我还将依赖项更新为

compile 'com.android.support:appcompat-v7:23.1.1'

匹配我的支持库在工具—> Android—> SDK管理器—> SDK工具选项卡—> Android支持库—>版本。 现在一切都好了。快乐编码:)

更改最新的SDK版本,这对我来说是工作

1.单击文件,然后单击项目结构 2.然后选择app 然后点击确定,这对我有用。