Android(安卓)GridView 异步加载图片

网上的资源普遍上是ListView异步加载图片，比较少有GirdView异步加载图片，参考了ListView异步加载图片的做法把GridView的异步加载图片功能做出来，方法和思想大同小异，本文章把GridView异步加载内存卡和网络图片希望对大家有用。效果图如下：

一、主界面代码：

import java.util.ArrayList;import java.util.List;import android.app.Activity;import android.os.Bundle;import android.widget.GridView;public class MainActivity extends Activity {    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        GridView gridView=(GridView)findViewById(R.id.gridview);        List list = new ArrayList();        String[] paths=new String[15];        for(int i=0;i<15;i++){        int index=i;        paths[i]="/sdcard/"+String.valueOf(index+1)+".jpg";//自己动手向SD卡添加15张图片，如：1.jpg        }        for(int i=0;i<15;i++){        list.add(new ImageAndText(paths[i], String.valueOf(i)));        }        gridView.setAdapter(new ImageAndTextListAdapter(this, list, gridView));    }}

二、以下代码是实现异步获取图片的主方法，SoftReference是软引用，是为了更好的为了系统回收变量，重复的URL直接返回已有的资源，实现回调函数，让数据成功后，更新到UI线程。

import java.io.IOException;import java.io.InputStream;import java.lang.ref.SoftReference;import java.net.MalformedURLException;import java.net.URL;import java.util.HashMap;import android.R.drawable;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.BitmapFactory.Options;import android.graphics.drawable.BitmapDrawable;import android.graphics.drawable.Drawable;import android.os.Handler;import android.os.Message;import android.util.Log;import android.widget.ImageView;public class AsyncImageLoader {     private HashMap> imageCache;     public AsyncImageLoader() {             imageCache = new HashMap>();         }           public Drawable loadDrawable(final String imageUrl, final ImageCallback imageCallback) {             if (imageCache.containsKey(imageUrl)) {                 SoftReference softReference = imageCache.get(imageUrl);                 Drawable drawable = softReference.get();                 if (drawable != null) {                     return drawable;                 }             }             final Handler handler = new Handler() {                 public void handleMessage(Message message) {                     imageCallback.imageLoaded((Drawable) message.obj, imageUrl);                 }             };             new Thread() {                 @Override                 public void run() {                     Drawable drawable = loadImageFromUrl(imageUrl);                     imageCache.put(imageUrl, new SoftReference(drawable));                     Message message = handler.obtainMessage(0, drawable);                     handler.sendMessage(message);                 }             }.start();             return null;         }           public static Drawable loadImageFromUrl(String url) {//    /**//     * 加载网络图片//     *///            URL m;//            InputStream i = null;//            try {//                m = new URL(url);//                i = (InputStream) m.getContent();//            } catch (MalformedURLException e1) {//                e1.printStackTrace();//            } catch (IOException e) {//                e.printStackTrace();//            }//            Drawable d = Drawable.createFromStream(i, "src");        /**     * 加载内存卡图片     */        Options options=new Options();        options.inSampleSize=2;        Bitmap bitmap=BitmapFactory.decodeFile(url, options);        Drawable drawable=new BitmapDrawable(bitmap);            return drawable;        }          public interface ImageCallback {             public void imageLoaded(Drawable imageDrawable, String imageUrl);                      }}

三、ImageAndTextListAdapter是实现ListView的Adapter，里面有个技巧就是 imageView.setTag(imageUrl)，setTag是存储数据的，这样是为了保证在回调函数时，listview去更新自己对应 item。

import java.util.List;import cn.wangmeng.test.AsyncImageLoader.ImageCallback;import android.app.Activity;import android.graphics.drawable.Drawable;import android.util.Log;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.ArrayAdapter;import android.widget.GridView;import android.widget.ImageView;import android.widget.ListView;import android.widget.TextView;public class ImageAndTextListAdapter extends ArrayAdapter {        private GridView gridView;        private AsyncImageLoader asyncImageLoader;        public ImageAndTextListAdapter(Activity activity, List imageAndTexts, GridView gridView1) {            super(activity, 0, imageAndTexts);            this.gridView = gridView1;            asyncImageLoader = new AsyncImageLoader();        }        public View getView(int position, View convertView, ViewGroup parent) {            Activity activity = (Activity) getContext();            // Inflate the views from XML            View rowView = convertView;            ViewCache viewCache;            if (rowView == null) {                LayoutInflater inflater = activity.getLayoutInflater();                rowView = inflater.inflate(R.layout.griditem, null);                viewCache = new ViewCache(rowView);                rowView.setTag(viewCache);            } else {                viewCache = (ViewCache) rowView.getTag();            }            ImageAndText imageAndText = getItem(position);            // Load the image and set it on the ImageView            String imageUrl = imageAndText.getImageUrl();            ImageView imageView = viewCache.getImageView();            imageView.setTag(imageUrl);            Drawable cachedImage = asyncImageLoader.loadDrawable(imageUrl, new ImageCallback() {                public void imageLoaded(Drawable imageDrawable, String imageUrl) {                    ImageView imageViewByTag = (ImageView) gridView.findViewWithTag(imageUrl);                    if (imageViewByTag != null) {                        imageViewByTag.setImageDrawable(imageDrawable);                    }                }            });            if (cachedImage == null) {                imageView.setImageResource(R.drawable.icon);            }else{                imageView.setImageDrawable(cachedImage);            }            // Set the text on the TextView            TextView textView = viewCache.getTextView();            textView.setText(imageAndText.getText());            return rowView;        }}

四、2个辅助类：

public class ImageAndText {    private String imageUrl;    private String text;    public ImageAndText(String imageUrl, String text) {        this.imageUrl = imageUrl;        this.text = text;    }    public String getImageUrl() {        return imageUrl;    }    public String getText() {        return text;    }}

public class ViewCache {    private View baseView;    private TextView textView;    private ImageView imageView;    public ViewCache(View baseView) {        this.baseView = baseView;    }    public TextView getTextView() {        if (textView == null) {            textView = (TextView) baseView.findViewById(R.id.text);        }        return textView;    }    public ImageView getImageView() {        if (imageView == null) {            imageView = (ImageView) baseView.findViewById(R.id.image);        }        return imageView;    }}

五、Xml配置文件，包括griditem和main：

1griditem：

<?xml version="1.0" encoding="UTF-8"?>

2main:

<?xml version="1.0" encoding="utf-8"?>

六、大功告成，总结方法。

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