Android_Java(22) - ActivityLifeCycle

1. 액티비티 생명주기
    1) 생성부터 소멸까지의 주기 
    2) 앱은 화면이 작아 동시에 여러 개의 액티비티(화면)가 나올 수 없음 
        - 앞에 나오는 화면 하나만 활성화된 상태이고, 나머지는 모두 비활성화된 상태로 남게됨 
    3) 실행상태(resumed, running)
        - 액티비티가 전경에 위치하고 있으며, 사용자의 포커스를 가지고 있음 
       일시멈춤상태(paused)
        - 다른 액티비티가 전경에 있으며, 포커스를 가지고 있으며 현재 액티비티의 일부가 아직도 화면에 보이고 있는 상태 
       정지상태(stoped)
        - 액티비티는 배경에 위치함 
    4) 콜백 메서드  
        - onCreate()
            - 액티비티가 생성되면서 호출
            - 중요한 구성요소를 초기화 
        - onPause()
            - 사용자가 액티비티를 떠나고 있을 때, 이 메소드가 호출
            - 그 동안 이루어졌으면, 변경사항을 저장 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/btnDial"
        android:text="전화걸기"/>
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/btnFinish"
        android:text="끝내기"/>
</LinearLayout>

package kr.co.activitylifecycle;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        getSupportActionBar().setDisplayShowHomeEnabled(true);
        getSupportActionBar().setIcon(R.drawable.ic_launcher);
        setTitle("액티비티 라이프사이클");

        Log.i("액티비티 생명주기", " onCreate()");

        Button btnDial = findViewById(R.id.btnDial);
        btnDial.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Uri uri = Uri.parse("tel:02-532-6509");
                Intent intent = new Intent(Intent.ACTION_DIAL, uri);
                startActivity(intent);
            }
        });

        Button btnFinish = findViewById(R.id.btnFinish);
        btnFinish.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i("액티비티 생명주기", " onDestroy()");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.i("액티비티 생명주기", " onPause()");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.i("액티비티 생명주기", " onRestart()");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.i("액티비티 생명주기", " onResume()");
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.i("액티비티 생명주기", " onStart()");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.i("액티비티 생명주기", " onStop()");
    }
}

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[결과출력]

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