LISTVIEW动态加载网络数据2

最新推荐文章于 2025-11-26 16:17:36 发布

最新推荐文章于 2025-11-26 16:17:36 发布 · 76 阅读

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本文深入探讨了Android中ListView的滚动加载机制，包括如何在滚动到最底部时加载剩余元素，以及如何实现异步加载图片资源，以提升用户体验。详细介绍了滚动监听器的使用、滚动翻页功能的实现，以及利用SoftReference优化内存管理。同时，通过具体的代码实例展示了如何在Adapter中异步加载图片，并确保UI线程更新操作的正确性。

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  }