안드로이드 ListView

<?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"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

        <ListView  //ListView 생성
            android:id="@+id/list" //id 생성 id 이름 list
            android:layout_width="match_parent" //넓이
            android:layout_height="wrap_content"> //높이


        </ListView>

</LinearLayout>

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package com.example.listexample01;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private ListView list; //ListView 변수 생성

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        list =(ListView)findViewById(R.id.list);  //ListView를 변수 list에 넣어줌

        List<String> data = new ArrayList<>();  //List생성

        ArrayAdapter<String> adapter = new ArrayAdapter<>(this,android.R.layout.simple_list_item_1,data);  //ListView와 List를 연결하기 위한 adapter 생성 this(현재 Activity)에  android.R.layout.simple_list_item_1 사용할 List 형태 
        list.setAdapter(adapter);  //ListView와 List를 연결

        data.add("Hello World");  //List에 Data를 추가
        data.add("A");
        data.add("B");
        data.add("C");
        adapter.notifyDataSetChanged();  //저장 

    }
}