[JAVA] 안드로이드 LiveData 초간단 예제 (ViewModel 안 쓰고)

이번에는 라이브 데이터만 다루는 예제이다

 

1. MainActivity

package com.monkey.viewmodeltest;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;

import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    TextView tvNormal;
    Button btnPlus, btnMinus;

    MutableLiveData<Integer> normalCount = new MutableLiveData<Integer>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        normalCount.setValue(0);

        tvNormal = findViewById(R.id.tv_normal);
        btnPlus = findViewById(R.id.btn_plus);
        btnMinus = findViewById(R.id.btn_minus);

        normalCount.observe(this, new Observer<Integer>() {
            @Override
            public void onChanged(Integer integer) {
                setCountText();
            }
        });

        btnPlus.setOnClickListener(v-> {
            normalCount.setValue(normalCount.getValue()+1);
        });

        btnMinus.setOnClickListener(v-> {
            normalCount.setValue(normalCount.getValue()-1);
        });
    }

    @Override
    protected void onResume() {
        super.onResume();
        setCountText();
    }

    private void setCountText() {
        tvNormal.setText(normalCount.getValue() +"");
    }
}

 

2. activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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">

    <Button
        android:id="@+id/btn_minus"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="-"
        app:layout_constraintTop_toBottomOf="@id/tv_normal"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@id/btn_plus" />

    <Button
        android:id="@+id/btn_plus"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="+"
        app:layout_constraintLeft_toRightOf="@id/btn_minus"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="@id/btn_minus"
        app:layout_constraintBottom_toBottomOf="@id/btn_minus"/>


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="NORMAL"
        android:textColor="@color/purple_500"
        android:textStyle="bold"
        app:layout_constraintLeft_toLeftOf="@id/tv_normal"
        app:layout_constraintRight_toRightOf="@id/tv_normal"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toTopOf="@id/tv_normal"
        app:layout_constraintVertical_bias="1"/>

    <TextView
        android:id="@+id/tv_normal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="0"
        android:textColor="#000"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

 

 

plus, minus 버튼에서 setText를 해 주지 않아도

값이 변하면 텍스트가 변하게 된다!