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Flutter plugin not installed; this adds Flutter specific functionality. windows

For windows 

// run on commandline
flutter config --android-studio-dir=C:Program FilesAndroidAndroid Studio

Flutter plugin not installed; this adds Flutter specific functionality

Solution that worked for me:
  1. Just install plugins.
  		Studio>>File>Settings>Plugins>Browse Repositories
  2. Search for flutter.
  3. Tap on Install (a dialog will pop regarding dart dependency. click Yes).
  4. Once the installation is finished restart android studio.

If still not worked
  1. flutter channel dev
  2. flutter doctor -v

flutter plugin installed but in flutter doctor it shows not installed

flutter channel dev
flutter upgrade
flutter config --android-studio-dir="C:Program FilesAndroidAndroid Studio"
flutter doctor -v

Flutter plugin not installed; this adds Flutter specific functionality.

// for android studio 4.2
ln -s ~/Library/Application Support/Google/AndroidStudio4.2/plugins ~/Library/Application Support/AndroidStudio4.2

Flutter plugin not installed; this adds Flutter specific functionality

ln -s ~/Library/Application Support/Google/AndroidStudio4.1/plugins ~/Library/Application Support/AndroidStudio4.1