I'm always using Android Studio's debugger to walk through the code and see how things work.
As I dive deeper into the SDK, I get to lisView.java for example, and now it's class members are mostly red? (see link)
Why is that?? I could see my code and parts of the SDK prior to 'stepping in' listView.java? Why suddenly is it all red on the right-had column?
As you see in the screenshot, now I can't see the value for
the member variable, mOldItemCount for example.
Try file -> invalidate caches / restart -> Invalidate caches and restart
Sync Gradle and Rebuild Project.
Possible Fixes:
- Sync Gradle
- Restart Android Studio
- Clean and Rebuild
A Possible other problem that can occur is that you moved the location of the file. Its happened to me before.
When you have a red code like the image is because the autogenerate files and de gradle its not working well.
I try this options in order:
First, Check de import and be sure are the rigth imports
Second, Sync Gradle and Rebuild Project.
Third, Clean project
If the problem persist try checking the android dependencies and see which one is creating the problem.
Try deleting .gradle and .idea folder of project. For me its solved the problem.
Just removing .idea or at least files inside of it, even if while you're opening Android Studio a popup alert will be shown to tell you to reload your project and it everything will go back normally
来源：https://stackoverflow.com/questions/41665873/why-is-the-source-code-all-red-in-android-studio