Android中点击button，实现ImageView中图片的循环切换

package ztestchangedpicture;

import com.example.ztestchangedpicture.R;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;

public class ChangedPicture extends Activity {

    private Button forChange;
    private ImageView forDisplay;
    int[] image = {R.drawable.img_temp_16,R.drawable.img_temp_17,R.drawable.img_temp_18,R.drawable.img_temp_19};
    int counts = 0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.changed_picture);
        forChange = (Button) findViewById(R.id.btn_click);
        forDisplay = (ImageView) findViewById(R.id.img_display);
        
        forDisplay.setImageResource(image[0]);
        
        forChange.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                //因为数组中有4张图片，第一张已默认。
                if(counts >= 3){
                    counts = -1;//
                }
                /*counts初始值为0，所以不执行if判断，直接执行下面的语句，而数据的第一张图片已默认，
                 * 所以++counts的值为1，依次当点击第三次时，counts值为2，而++counts为3，再次点击时就执行if判断，将-1
                 * 赋值给counts，再执行下面的语句，++counts为0，重新开始*/
                forDisplay.setImageResource(image[++counts]);
            }
        });
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >
    
    <Button
        android:id="@+id/btn_click"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="changed picture for click" />
    
    <ImageView
        android:id="@+id/img_display"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp"
        android:layout_gravity="center" />

</LinearLayout>