Android_Java(4) - RatingBarApp

<이벤트 처리>

1. 이벤트 구동 방식
    1) 터치하면 바로 처리됨 => 폴링(polling) 방식 
    2) 다른 작업을 하고 있을테니 터치하면 알려줌 => 이벤트 구동 (event-driven) 방식 

2. 안드로이드에서 이벤트 처리 방법
    1) 이벤트 처리 객체를 생성하여 컴포넌트에 등록
    2) 뷰 클래스의 이벤트 처리 메소드를 재정의 
        - 버튼에 붙은 리스너 객체가 이벤트를 처리함 
    3) 이벤트 리스너                        콜백 메서드                 설명
       =====================================================================================
        - View.OnClickListener           onClick()              사용자가 어떤 항목을 터치하거나 엔터키를 눌러서 선택하면 호출됨
        - View.OnKeyListener             onKey()                키를 눌렀다가 놓았을 때 호출됨 
        - View.OnTouchListener         onTouch()            사용자가 터치 이벤트로 간주되는 동작을 한 경우에 호출됨 
    4) 리스너 객체를 생성하는 방법 
        - 리스너 클래스를 익명 클래스로 정의함 (가장 많이 사용되는 방법)
            - 익명클래스 : 클래스 몸체는 정의되지만, 이름이 없는 클래스임 
                        클래스를 정의하면서 동시에 객체를 생성하게 됨 

---

<MainActivity.java>

package kr.co.ratingbarapp;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.RatingBar;
import android.widget.Toast;

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);

        final RatingBar ratingBar = findViewById(R.id.ratingbar);
        ratingBar.setOnRatingBarChangeListener(new RatingBar.OnRatingBarChangeListener() {
            @Override
            public void onRatingChanged(RatingBar ratingBar, float v, boolean b) {
                Toast.makeText(getApplicationContext(), "New Rating : " + v, Toast.LENGTH_SHORT).show();
            }
        });
    }
}

<activity_main.xml>

<?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="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <RatingBar
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/ratingbar"
        android:numStars="5"
        android:stepSize="1.0"/>

</LinearLayout>​

<결과 출력>