3-3-3 액티비티 수명주기

MainActivity

package com.example.boostcoursepractice;
 
import androidx.annotation.Nullable;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
 
import android.app.Activity;
import android.content.ComponentName;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.FrameLayout;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
 
import com.google.android.material.snackbar.Snackbar;
 
import org.w3c.dom.Text;
 
import java.lang.reflect.Array;
import java.util.ArrayList;
 
 
public class MainActivity extends AppCompatActivity {
 
    Button closeBtn ;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        Toast.makeText(this, "OnCreate() 호출됨", Toast.LENGTH_LONG).show();
 
        closeBtn = (Button) findViewById(R.id.btn_close);
        closeBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });
    }
 
    @Override
    protected void onPostCreate(@Nullable Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
    }
 
    @Override
    protected void onStart() {
        super.onStart();
        Toast.makeText(this, " onStart() 호출됨", Toast.LENGTH_LONG).show();
    }
 
    @Override
    protected void onStop() {
        super.onStop();
        Toast.makeText(this, "onStop() 호출됨", Toast.LENGTH_LONG).show();
    }
 
    @Override
    protected void onDestroy() {
        super.onDestroy();
        Toast.makeText(this, "onDestroy() 호출됨", Toast.LENGTH_LONG).show();
    }
 
    @Override
    protected void onPause() {
        super.onPause();
        Toast.makeText(this, "onPause() 호출됨", Toast.LENGTH_LONG).show();
 
        SharedPreferences pref = getSharedPreferences("pref", Activity.MODE_PRIVATE);
        if(pref == null) Toast.makeText(this, "pref가 없습니다.", Toast.LENGTH_LONG).show();
        SharedPreferences.Editor editor = pref.edit();
        editor.putString("name", "소녀시대");
        editor.commit() ;
    }
 
    @Override
    protected void onResume() {
        super.onResume();
        Toast.makeText(this, "onResume() 호출됨", Toast.LENGTH_LONG).show();
 
        SharedPreferences pref = getSharedPreferences("pref", Activity.MODE_PRIVATE);
        if(pref == null) Toast.makeText(this, "pref가 없습니다.", Toast.LENGTH_LONG).show();
        if(pref != null)
        {
            String name = pref.getString("name", "");
            Toast.makeText(this, "복구된 데이터 : " + name, Toast.LENGTH_LONG).show();
        }
    }
 
    @Override
    protected void onRestart() {
        super.onRestart();
 
        Toast.makeText(this, "onRestart() 호출됨", Toast.LENGTH_LONG).show();
    }
}
 

 

액티비티 수명주기는 아래 그림과 같다.

 

추가적으로 간단한 데이터베이스인 

  SharedPreferences pref = getSharedPreferences("pref", Activity.MODE_PRIVATE);

가 있는데 key값과 value값을 이용하여 사용한다.(getSharedPreferences를 하는 순간부터 pref는 null값을 가지지 않는다)