Android 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<ImageAndText> list = new ArrayList<ImageAndText>();              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<String, SoftReference<Drawable>> imageCache;       public AsyncImageLoader() {               imageCache = new HashMap<String, SoftReference<Drawable>>();           }               public Drawable loadDrawable(final String imageUrl, final ImageCallback imageCallback) {               if (imageCache.containsKey(imageUrl)) {                   SoftReference<Drawable> 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>(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<ImageAndText> {                    private GridView gridView;              private AsyncImageLoader asyncImageLoader;              public ImageAndTextListAdapter(Activity activity, List<ImageAndText> 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：

1、griditem：

<?xml version="1.0" encoding="UTF-8"?>      <RelativeLayout               xmlns:android="http://schemas.android.com/apk/res/android"             android:layout_height="100dip"               android:paddingBottom="4dip" android:layout_width="fill_parent">           <ImageView                  android:id="@+id/image"                 android:layout_height="80dip"                 android:layout_width="80dip"                 android:layout_centerHorizontal="true"                 android:scaleType="centerCrop">           </ImageView>           <TextView                 android:id="@+id/text"                    android:layout_width="wrap_content"                 android:layout_height="wrap_content"                 android:layout_below="@+id/image"                 android:layout_centerHorizontal="true"                 >           </TextView>  </RelativeLayout>

2、main

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"      android:orientation="vertical" android:layout_width="fill_parent"      android:layout_height="fill_parent">            <GridView xmlns:android="http://schemas.android.com/apk/res/android"          android:id="@+id/gridview"         android:layout_width="fill_parent"          android:layout_height="fill_parent"         android:numColumns="4"         android:verticalSpacing="10dp"         android:horizontalSpacing="10dp"         android:columnWidth="80dp"      android:stretchMode="columnWidth"         android:gravity="center"       android:background="#ffffff"   />   </LinearLayout> 

文件出处：http://blog.csdn.net/lanpy88/article/details/6671915