[Do it! Android] 도전! 1. 한 화면에 두 개의 이미지 뷰 배치하기(2개의 이미지 Change)

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:id="@+id/topImage"
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:src="@drawable/rock"
        android:layout_alignParentTop="true"
        />
    <ImageView
        android:id="@+id/bottomImage"
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:src="@drawable/paper"
        android:layout_alignParentBottom="true"
        />

    <Button
        android:id="@+id/topButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/topImage"
        android:text="위"
        android:onClick="topButton"
        />
    <Button
        android:id="@+id/bottomButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignTop="@+id/bottomImage"
        android:layout_alignParentRight="true"
        android:text="아래"
        android:onClick="bottomButton"
        />


</RelativeLayout>

MainActivity.java

package org.androidtown.a2_1;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {

    ImageView topImage;
    ImageView bottomImage;
    Button topButton;
    Button bottomButton;
    Boolean check = true;

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

        topImage = (ImageView) findViewById(R.id.topImage);
        bottomImage = (ImageView) findViewById(R.id.bottomImage);

        topButton = (Button) findViewById(R.id.topButton);
        bottomButton = (Button) findViewById(R.id.bottomButton);
    }

    public void topButton(View v){
        changeImage();
    }

    public void bottomButton(View v){
        changeImage();
    }

    private void changeImage(){
        if(check == true){
            check = false;
            topImage.setImageResource(R.drawable.paper);
            bottomImage.setImageResource(R.drawable.rock);
        }else{
            check = true;
            topImage.setImageResource(R.drawable.rock);
            bottomImage.setImageResource(R.drawable.paper);
        }
    }
}