LISTVIEW动态加载网络数据2-优快云博客

写的有点乱，但是写的挺好的。

转自：http://www.cnblogs.com/Greenwood/archive/2011/04/02/2003170.html

总体框架：

1.滚动加载

listView.setOnScrollListener(new OnScrollListener() {
//添加滚动条滚到最底部，加载余下的元素
@Override
publicvoidonScrollStateChanged(AbsListView view,int scrollState) {
if(scrollState== OnScrollListener.SCROLL_STATE_IDLE) {
loadRemnantListItem();
}
}
@Override
publicvoidonScroll(AbsListView view,intfirstVisibleItem,intvisibleItemCount,int totalItemCount) {}
});

listView.setOnItemSelectedListener(new OnItemSelectedListener() {
//按键选择List中的item，焦点落在最下面的view上加载余下的item
@Override
publicvoidonItemSelected(AdapterView<?>parent, View view,intposition,long id) {
if(footerView== view) {
loadRemnantListItem();
listView.setSelection(position-1 );
}
}
@Override
publicvoidonNothingSelected(AdapterView<?> parent) {}
});

privatevoidloadRemnantListItem() {// 滚到加载余下的数据
// 动态的改变listAdapter.getCount()的返回值
//使用Handler调用listAdapter.notifyDataSetChanged();更新数据
}

2.滚动翻页

//listView监听器代码相同
privatevoidloadRemnantListItem() {// 滚到加载余下的数据
// 重新listView.setAdapter(newsAdapter);
//使用Handler调用listAdapter.notifyDataSetChanged();更新数据
}

注：在listView最下面可以使用listView.addFooterView(footerView, null, true);来显示“加载中...”等的字样来美化用户体验，在loadRemnantListItem()方法中动态控制“加载中...”的显示和不显示。

具体例子1:

ListView异步加载图片是非常实用的方法，凡是是要通过网络获取图片资源一般使用这种方法比较好，用户体验好，不用让用户等待下去，下面就说实现方法，先贴上主方法的代码：

package cn.wangmeng.test;

importJava.io.IOException;
import java.io.InputStream;
import java.lang.ref.SoftReference;
import java.NET.MalformedURLException;
import java.net.URL;
import java.util.HashMap;

importAndroid.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。

ViewCache是辅助获取adapter的子元素布局

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;
}

}

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,大家仔细阅读就知道了。

具体例子2:

 01  packagecn.riddles.activity; 
 
     02  
 
     03  importandroid.app.Activity; 
 
     04  importandroid.os.Bundle; 
 
     05  importandroid.widget.ListView; 
 
     06  
 
     07  publicclassMainActivityextendsActivity { 
 
     08  privateListView lv; 
 
     09  @Override 
 
     10  publicvoidonCreate(Bundle savedInstanceState) { 
 
     11  super.onCreate(savedInstanceState); 
 
     12  setContentView(R.layout.main); 
 
     13  lv = (ListView)this.findViewById(R.id.test_lv); 
 
     14  lv.setAdapter(newSongListAdapter(this)); 
 
     15  } 
 
     16  } 
 
        01  packagecn.riddles.activity; 
 
        02  
 
        03  importandroid.content.Context; 
 
        04  importandroid.util.Log; 
 
        05  importandroid.view.LayoutInflater; 
 
        06  importandroid.view.View; 
 
        07  importandroid.view.ViewGroup; 
 
        08  importandroid.widget.BaseAdapter; 
 
        09  importandroid.widget.ImageView; 
 
        10  importandroid.widget.TextView; 
 
        11  /** 
 
        12  * @author riddlezhang 歌曲条目适配器 
 
        13  */ 
 
        14  publicclassSongListAdapterextendsBaseAdapter { 
 
        15  privatestaticfinalString TAG ="SongListAdapter"; 
 
        16  privateContext mContext; 
 
        17  privateString[] strings = {"王力宏","吴尊","何润东","金城武","吴彦祖"}; 
 
        18  privateString[] paths = {"http://list.image.baidu.com/t/image_category/galleryimg/menstar/hk/wang_li_hong.jpg", 
 
        19  "http://list.image.baidu.com/t/image_category/galleryimg/menstar/hk/wu_zun.jpg", 
 
        20  "http://list.image.baidu.com/t/image_category/galleryimg/menstar/hk/he_run_dong.jpg", 
 
        21  "http://list.image.baidu.com/t/image_category/galleryimg/menstar/hk/jin_cheng_wu.jpg", 
 
        22  "http://list.image.baidu.com/t/image_category/galleryimg/menstar/hk/wu_yan_zu.jpg"}; 
 
        23  publicSongListAdapter(Context mContext) { 
 
        24  this.mContext = mContext; 
 
        25  } 
 
        26  
 
        27  publicvoidsetmContext(Context mContext) { 
 
        28  this.mContext = mContext; 
 
        29  } 
 
        30  
 
        31  publicintgetCount() { 
 
        32  returnpaths.length; 
 
        33  } 
 
        34  
 
        35  publicObject getItem(intposition) { 
 
        36  returnposition; 
 
        37  } 
 
        38  
 
        39  publiclonggetItemId(intposition) { 
 
        40  returnposition; 
 
        41  } 
 
        42  
 
        43  publicView getView(intposition, View convertView, ViewGroup parent) { 
 
        44  convertView = LayoutInflater.from(mContext).inflate(R.layout.lv_adapter,null); 
 
        45  ImageView image = (ImageView) convertView.findViewById(R.id.image); 
 
        46  TextView songer = (TextView) convertView.findViewById(R.id.songer); 
 
        47  image.setTag(paths[position]); 
 
        48  songer.setText(strings[position]); 
 
        49  newCanvasImageTask().execute(image);//异步加载图片 
 
        50  Log.i(TAG,"execute:"+strings[position]); 
 
        51  returnconvertView; 
 
        52  } 
 
        53   
 
        54  } 
 
     view source 
     print 
     ? 
    
     01  packagecn.riddles.activity; 
 
     02  
 
     03  importjava.io.InputStream; 
 
     04  importjava.net.HttpURLConnection; 
 
     05  importjava.net.URL; 
 
     06  
 
     07  importandroid.graphics.drawable.Drawable; 
 
     08  importandroid.os.AsyncTask; 
 
     09  importandroid.util.Log; 
 
     10  importandroid.view.View; 
 
     11  importandroid.webkit.URLUtil; 
 
     12  
 
     13  
 
     14  /** 
 
     15  * @author riddlezhang 
 
     16  * 异步加载图片 
 
     17  */ 
 
     18  publicclassAsyncViewTaskextendsAsyncTask<View, Void, Drawable>{ 
 
     19  privateView mView; 
 
     20  protectedDrawable doInBackground(View... views) { 
 
     21  Drawable drawable =null; 
 
     22  View view=views[0]; 
 
     23  if(view.getTag() !=null) { 
 
     24  try{ 
 
     25  if(URLUtil.isHttpUrl(view.getTag().toString())) {//如果为网络地址。则连接url下载图片 
 
     26  URL url =newURL(view.getTag().toString()); 
 
     27  HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 
 
     28  conn.setDoInput(true); 
 
     29  conn.connect(); 
 
     30  InputStream stream = conn.getInputStream(); 
 
     31  drawable = Drawable.createFromStream(stream,"src"); 
 
     32  stream.close(); 
 
     33  }else{//如果为本地数据，直接解析 
 
     34  drawable = Drawable.createFromPath(view.getTag().toString()); 
 
     35  } 
 
     36  }catch(Exception e) { 
 
     37  Log.v("img", e.getMessage()); 
 
     38  returnnull; 
 
     39  } 
 
     40  } 
 
     41  this.mView=view; 
 
     42  returndrawable; 
 
     43  } 
 
     44  
 
     45  protectedvoidonPostExecute(Drawable drawable) { 
 
     46  if(drawable !=null) { 
 
     47  this.mView.setBackgroundDrawable(drawable); 
 
     48  this.mView=null; 
 
     49  } 
 
     50  } 
 
     51  
 
 52  }