Cannot resolve symbol 'v4'

The error "Cannot resolve symbol 'v4'" typically occurs when the Android Support Library v4 is not properly imported or referenced in your project. To resolve this issue, you can follow these steps:

1. Open your project in Android Studio.
2. Go to the "app" module's build.gradle file.
3. Check if the dependency for the Android Support Library v4 is included in the dependencies block. It should look like this:

dependencies {
    implementation 'com.android.support:support-v4:28.0.0'
    // other dependencies...
}

4. If the dependency is missing, add it manually and sync your project.
5. After syncing, clean and rebuild your project.

This should resolve the "Cannot resolve symbol 'v4'" error by properly importing the Android Support Library v4 into your project.