[Android] instance

 

when to use? 

• Activity의 간단한 UI정보를 저장할 때
• portrait <-> landscape (세로 <->가로) 모드 변경 시 

 

ex) 화면 모드 전환 Activity Lifecycle

[소멸과정]
onPause() ->onSaveInstanceState() -> onStop() -> onDestroy() 
[재생성 과정]
onCreate() -> onStart() ->onRestoreInstanceState(savedInstanceState : Bundle) -> onResume() 
새로 액티비티를 생성하는데 이때 기존에 액티비티가 가지고 있던 정보가 사라짐.
(ex. EditText)

 

onSaveInstanceState (outState : Bundle)

 

outState : Bundle in which to place your saved state. This value can't be null

 

 

 

onRestoreInstanceState(savedInstanceState : Bundle)

when is it called? this method is called between onStatrt() and onPostCreate(Bundle)

 

 

Example

//outState – Bundle in which to place your saved state.
//    user가 명시적으로 activity를 닫거나 finish()호출시 다음 메소드는 호출되지않음.
    override fun onSaveInstanceState(outState: Bundle) {
//    입력했던것 저장
        Log.i("State", "save Instance")
        outState.putString("USER_NAME", user_name_input_editText.text.toString())
        outState.putString("USER_PHONE", user_phone_number_editText.text.toString())
        super.onSaveInstanceState(outState)
    }

    override fun onRestoreInstanceState(savedInstanceState: Bundle?) {
        Log.i("State", "Restore Instance")
        super.onRestoreInstanceState(savedInstanceState)
        savedInstanceState?.run {
            user_name_input_editText.setText(savedInstanceState.getString("USER_NAME"))
            user_phone_number_editText.setText(savedInstanceState.getString("USER_PHONE"))
        }
    }

 

 

※ 뒤로가기 onBackPressed()같은 메소드 호출시 해당 Activity 객체는 메모리에서 해제되기 때문에

onSaveInstanceState를 해봤자 의미가 없다 .

∵ 다시 activity를 생성할 때는 새로운 activity 객체가 생성되기 때문이다.

[Reference]

https://developer.android.com/reference/android/app/Activity#onSaveInstanceState(android.os.Bundle)