上一篇講到ImageView，這篇利用Button切換ImageView的圖片，
可以讓圖片跳至上一張及下一張。
首先在xml檔新增ImageView及切換上下張圖片的2個Button
接著把要切換的圖片放置於專案名稱\app\src\main\res\drawable裡
在imageView裡先放第一張顯示的圖

xml範例如下:

<?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" >
    <ImageView
        android:id="@+id/imageView"
        android:layout_width="300dp"
        android:layout_height="300dp"
        android:layout_marginTop="50dp"
        android:layout_gravity="center"
        app:srcCompat="@drawable/lisa1" />
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="30dp"
        android:layout_gravity="center"
        android:orientation="horizontal">
        <Button
            android:id="@+id/buttonup"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="30sp"
            android:layout_weight="1"
            android:text="上一張圖片" />
        <Button
            android:id="@+id/buttonnext"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="30sp"
            android:text="下一張圖片" />
    </LinearLayout>
</LinearLayout>

接著到MainActivity.java來設定Button切換imageView的圖片

public class MainActivity extends AppCompatActivity {
    
    Button buttonup;
    Button buttonnext;
    ImageView imageView;

    private int[]  picture = {R.drawable.lisa1,R.drawable.jennie1,R.drawable.rose1,R.drawable.jisoo1};
    private int pictureIndex = 0;
    private int maxIndex = 3;

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

        buttonnext = (Button)findViewById(R.id.buttonnext);
        buttonup = (Button)findViewById(R.id.buttonup);
        imageView = (ImageView)findViewById(R.id.imageView);
        buttonup.setOnClickListener(this::onClick);
        buttonnext.setOnClickListener(this::onClick);
        imageView.setImageResource(picture[3]);
    }
    public void onClick(View view)
    {
        switch (view.getId())
        {
            case R.id.buttonnext:
                if (pictureIndex == maxIndex)
                {
                    pictureIndex = 0;
                }
                else
                {
                    pictureIndex = pictureIndex+1;
                }
                break;
            case R.id.buttonup:
                if (pictureIndex == 0)
                {
                    pictureIndex = maxIndex;
                }
                else
                {
                    pictureIndex = pictureIndex-1;
                }
                break;
            default:
                break;
        }
        imageView.setImageResource(picture[pictureIndex]);
    }

}