I\'m new to android development and I have this problem with my Android Studio 3.1.3 demo project or any project that I create.
Even though that I can drag and drop diff
Use stable version of support libraries.
The problem is when you are using unstable alpha support libraries. See stable libraries versions on google maven repo.
At the time of answer, most stable version of support:appcomact-v7
is 28.0.0-rc02
Replace
implementation 'com.android.support:appcompat-v7:28.0.0-alpha3' // less stable alpha
With
implementation 'com.android.support:appcompat-v7:28.0.0-rc02' // more stable
Sync, Just Restart AS. Problem resolved !