Android初学者之Listview异步加载网络图片并动态更新

应用实例:解析后台返回的数据,把每条都显示在ListView中,包括活动图片、店名、活动详情、地址、电话和距离等。

在布局文件中ListView的定义:

<ListView android:id="@id/maplistview" android:background="@drawable/bg" android:layout_width="fill_parent" android:layout_height="fill_parent" android:cacheColorHint="#00000000"  android:divider="@drawable/separator" android:dividerHeight="2.0px" android:layout_below="@id/mapseparator"/>


在布局文件ListViewItem,中定义活动图片、店名、活动详情、地址、电话和距离的布局:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout android:id="@+id/RelativeLayout01" android:layout_width="fill_parent" xmlns:android=" android:layout_height="wrap_content" android:paddingBottom="2dip" android:paddingLeft="2dip" android:paddingRight="2dip">
<ImageView android:paddingTop="2dip" android:layout_alignParentLeft="true" android:layout_width="80px"  android:layout_height="80px" android:id="@+id/maplistviewitemImage"/>
<TextView android:layout_height="wrap_content" android:textSize="17dip"  android:layout_width="fill_parent" android:id="@+id/maplistviewitemshopname"android:layout_toRightOf="@id/maplistviewitemImage"android:textColor="#000000"/>
<TextView android:layout_height="wrap_content" android:layout_width="fill_parent" android:layout_alignParentLeft="true" android:layout_below="@+id/maplistviewitemImage" android:id="@+id/maplistviewitemActi" android:textColor="#6C6C6C"/>
<TextView android:layout_height="wrap_content" android:layout_width="fill_parent" android:layout_alignParentLeft="true" android:layout_below="@+id/maplistviewitemActi" android:id="@+id/maplistviewitemaddr" android:textColor="#6C6C6C" android:singleLine="true"/>
<TextView android:layout_height="wrap_content" android:layout_width="fill_parent" android:layout_alignParentLeft="true" android:layout_below="@+id/maplistviewitemaddr" android:id="@+id/maplistviewitemtelphone" android:textColor="#6C6C6C" android:singleLine="true"/>
</RelativeLayout>

(1)定义类MapListImageAndText管理ListViewItem中控件的内容

package com.google.zxing.client.android.AsyncLoadImage;
 
public class MapListImageAndText {

        private String imageUrl;

        private String shopname;

        private String activitynifo;

        private String address;

        private String telephone;

        private String distance;
         

        public MapListImageAndText(String imageUrl, String shopname, String activitynifo, String address, String telephone,String distance) {

            this.imageUrl = imageUrl;

            this.shopname = shopname;

            this.activitynifo = activitynifo;

            this.address = address;

            this.telephone = telephone;

            this.distance=distance;

        }
 

        public String getImageUrl() {

            return imageUrl;

        }
         

        public String getShopname() {

            return shopname;

        }
 

        public String getActivitynifo() {

            return activitynifo;

        }
 

        public String getAddress() {

            return address;

        }
 

        public String getTelephone() {

            return telephone;

        }
         

        public String getDistance() {

            return distance;

        }
 
         
}


(2)定义类MapListViewCache实例化ListViewItem中的控件

package com.google.zxing.client.android.AsyncLoadImage;
 
import com.google.zxing.client.android.R;
 
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;
 
public class MapListViewCache {
 

        private View baseView;

        private TextView shopname;

        private TextView activitynifo;

        private TextView address;

        private TextView telephone;

        private TextView distance;
 

        private ImageView imageView;
 

        public MapListViewCache(View baseView) {

            this.baseView = baseView;

        }
 

        public TextView getShopname() {

            if (shopname == null) {

                shopname = (TextView) baseView.findViewById(R.id.maplistviewitemshopname);

            }

            return shopname;

        }
         

        public TextView getActivitynifo() {

            if (activitynifo == null) {

                activitynifo = (TextView) baseView.findViewById(R.id.maplistviewitemActi);

            }

            return activitynifo;

        }
         

        public TextView getAddress() {

            if (address == null) {

                address = (TextView) baseView.findViewById(R.id.maplistviewitemaddr);

            }

            return address;

        }
         

        public TextView getTelephone() {

            if (telephone == null) {

                telephone = (TextView) baseView.findViewById(R.id.maplistviewitemtelphone);

            }

            return telephone;

        }
 

        public ImageView getImageView() {

            if (imageView == null) {

                imageView = (ImageView) baseView.findViewById(R.id.maplistviewitemImage);

            }

            return imageView;

        }
         

        public TextView getDistance() {

            if (distance == null) {

                distance = (TextView) baseView.findViewById(R.id.maplistviewitemdistance);

            }

            return distance;

        }
 
}


(3)定义类AsyncImageLoader,开启线程下载指定图片

package com.google.zxing.client.android.AsyncLoadImage;
 
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);

         }
 
}


(4)定义类MapListImageAndTextListAdapter继承ArrayAdapter,用于创建AsyncImageLoader实例,并指定控件的内容:

package com.google.zxing.client.android.AsyncLoadImage;
 
import java.util.List;
 
import com.google.zxing.client.android.R;
 
import com.google.zxing.client.android.AsyncLoadImage.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 MapListImageAndTextListAdapter extends ArrayAdapter<MapListImageAndText> {
 

        private ListView listView;

        private AsyncImageLoader asyncImageLoader;
 

        public MapListImageAndTextListAdapter(Activity activity, List<MapListImageAndText> 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;

            MapListViewCache viewCache;

            if (rowView == null) {

                LayoutInflater inflater = activity.getLayoutInflater();

                rowView = inflater.inflate(R.layout.maplistviewitem, null);

                viewCache = new MapListViewCache(rowView);

                rowView.setTag(viewCache);

            } else {

                viewCache = (MapListViewCache) rowView.getTag();

            }

            MapListImageAndText 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.refresh);

            }else{

                imageView.setImageDrawable(cachedImage);

            }

            // Set the text on the TextView

            TextView shopname = viewCache.getShopname();

            shopname.setText(imageAndText.getShopname());
             

            TextView activitynifo = viewCache.getActivitynifo();

            activitynifo.setText(imageAndText.getActivitynifo());
             

            TextView address = viewCache.getAddress();

            address.setText(imageAndText.getAddress());
             

            TextView telephone = viewCache.getTelephone();

            telephone.setText(imageAndText.getTelephone());
             

            TextView distance = viewCache.getDistance();

            distance.setText(imageAndText.getDistance());
             

            return rowView;

        }
 
}


(5)主程序中Listview与MapListImageAndTextListAdapter的捆绑

//tuangoupoints为对后台传回来的数据解析后得到的字符串
String mtuangoupoints =tuangoupoints.split("@");
 
List<MapListImageAndText> dataArray=new ArrayList<MapListImageAndText>();
     
for(int i=0; i<mtuangoupoints.length;i++){

    String tonepoint=mtuangoupoints[i].split("#");
     

    String shopname=String.valueOf(i+1)+tonepoint[2];

    String activityinfo=tonepoint[1];

    String address=tonepoint[6];

    String telephone=tonepoint[7];

    String imageurl=tonepoint[8];

    String distance=tonepoint[5];
     

    MapListImageAndText test=new MapListImageAndText(imageurl,shopname,activityinfo,address,telephone,distance);

    dataArray.add(test);
}
     
MapListImageAndTextListAdapter adapter=new MapListImageAndTextListAdapter(this, dataArray, mlistView);
mlistView.setAdapter(adapter);[/i]


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