android中listView實現異步加載網絡圖片

 

ListView異步加載圖片是非常實用的方法，凡是是要通過網絡獲取圖片資源一般使用這種方法比較好，用戶體驗好，下面就說實現方法，先貼上主方法的代碼：
package cn.wangmeng.test; 
 
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.graphics.drawable.Drawable; 
import android.os.Handler; 
import android.os.Message; 
 
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) { 
            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"); 
            return d; 
        } 
       
         public interface ImageCallback { 
             public void imageLoaded(Drawable imageDrawable, String imageUrl); 
         } 
 
} 
package cn.wangmeng.test;

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.graphics.drawable.Drawable;
import android.os.Handler;
import android.os.Message;

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) {
   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");
   return d;
  }
  
      public interface ImageCallback {
          public void imageLoaded(Drawable imageDrawable, String imageUrl);
      }

}

以上代碼是實現異步獲取圖片的主方法，SoftReference是軟引用，是爲了更好的爲了系統回收變量，重複的URL直接返回已有的資源，實現回調函數，讓數據成功後，更新到UI線程。
幾個輔助類文件：
package cn.wangmeng.test; 
 
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; 
        } 
} 
Java代碼
package cn.wangmeng.test; 
 
import android.view.View; 
import android.widget.ImageView; 
import android.widget.TextView; 
 
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; 
        } 
 
} 
package cn.wangmeng.test;

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;
     }
}
package cn.wangmeng.test;

import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;

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;
     }

}
ViewCache是輔助獲取adapter的子元素佈局

package cn.wangmeng.test; 
 
import java.util.List; 
 
import cn.wangmeng.test.AsyncImageLoader.ImageCallback; 
 
import android.app.Activity; 
import android.graphics.drawable.Drawable; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ArrayAdapter; 
import android.widget.ImageView; 
import android.widget.ListView; 
import android.widget.TextView; 
 
public class ImageAndTextListAdapter extends ArrayAdapter<ImageAndText> { 
 
        private ListView listView; 
        private AsyncImageLoader asyncImageLoader; 
 
        public ImageAndTextListAdapter(Activity activity, List<ImageAndText> imageAndTexts, ListView listView) { 
            super(activity, 0, imageAndTexts); 
            this.listView = listView; 
            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.image_and_text_row, 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) listView.findViewWithTag(imageUrl); 
                    if (imageViewByTag != null) { 
                        imageViewByTag.setImageDrawable(imageDrawable); 
                    } 
                } 
            }); 
            if (cachedImage == null) { 
                imageView.setImageResource(R.drawable.default_image); 
            }else{ 
                imageView.setImageDrawable(cachedImage); 
            } 
            // Set the text on the TextView 
            TextView textView = viewCache.getTextView(); 
            textView.setText(imageAndText.getText()); 
 
            return rowView; 
        } 
 
} 
package cn.wangmeng.test;

import java.util.List;

import cn.wangmeng.test.AsyncImageLoader.ImageCallback;

import android.app.Activity;
import android.graphics.drawable.Drawable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

public class ImageAndTextListAdapter extends ArrayAdapter<ImageAndText> {

     private ListView listView;
     private AsyncImageLoader asyncImageLoader;

     public ImageAndTextListAdapter(Activity activity, List<ImageAndText> imageAndTexts, ListView listView) {
         super(activity, 0, imageAndTexts);
         this.listView = listView;
         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.image_and_text_row, 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) listView.findViewWithTag(imageUrl);
                 if (imageViewByTag != null) {
                     imageViewByTag.setImageDrawable(imageDrawable);
                 }
             }
         });
   if (cachedImage == null) {
    imageView.setImageResource(R.drawable.default_image);
   }else{
    imageView.setImageDrawable(cachedImage);
   }
         // Set the text on the TextView
         TextView textView = viewCache.getTextView();
         textView.setText(imageAndText.getText());

         return rowView;
     }

}

ImageAndTextListAdapter是實現ListView的Adapter，裏面有個技巧就是imageView.setTag(imageUrl)，setTag是存儲數據的，這樣是爲了保證在回調函數時，listview去更新自己對應item,大家仔細閱讀就知道了。
最後貼出佈局文件：

Xml代碼
<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
              android:orientation="horizontal" 
              android:layout_width="fill_parent" 
              android:layout_height="wrap_content"> 
 
        <ImageView android:id="@+id/image" 
                   android:layout_width="wrap_content" 
                   android:layout_height="wrap_content" 
                   /> 
 
        <TextView android:id="@+id/text" 
                  android:layout_width="wrap_content" 
                  android:layout_height="wrap_content"/> 
 
</LinearLayout> 
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="horizontal"
              android:layout_width="fill_parent"
              android:layout_height="wrap_content">

        <ImageView android:id="@+id/image"
                   android:layout_width="wrap_content"
                   android:layout_height="wrap_content"
                   />

        <TextView android:id="@+id/text"
                  android:layout_width="wrap_content"
                  android:layout_height="wrap_content"/>

</LinearLayout>

 

轉載：http://blog.csdn.net/zeng622peng/article/details/5912431