How to change theme from another app resource in android?

So, what should I do to use a theme from different package resource?

You shouldn't do this for many reasons. I wrote a simple project that shows that it is indeed possible as long as the package contains the resources your activity uses.

See: https://github.com/jaredrummler/SO-41872033

Basically, you would need to return the package's resources from the activity:

java

public class MainActivity extends AppCompatActivity {

  Resources resources;

  @Override protected void onCreate(Bundle savedInstanceState) {

    int themeResId = getResources().getIdentifier("AppTheme", "style", "com.example.theme");
    if (themeResId != 0) {
      setTheme(themeResId);
    }

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
  }

  @Override public Resources getResources() {
    if (resources == null) {
      try {
        resources = getPackageManager().getResourcesForApplication("com.example.theme");
      } catch (PackageManager.NameNotFoundException e) {
        resources = super.getResources();
      }
    }
    return resources;
  }

}

This is just to show that it is possible. Again, I recommend that you avoid this.