• Listview动态加载网络数据

    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
    public void onScrollStateChanged(AbsListView view, int     scrollState) {
    if (scrollState ==     OnScrollListener.SCROLL_STATE_IDLE) {
    loadRemnantListItem();
    }
    }
    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, 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
    public void onItemSelected(AdapterView<?> parent, View view, int position, long     id) {
    if(footerView ==     view) {
    loadRemnantListItem();
    listView.setSelection(position     - 1    );
    }
    }
    @Override
    publicvoid onNothingSelected(AdapterView<?>     parent) {}
    });

    privatevoid loadRemnantListItem() {//    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
    privatevoid loadRemnantListItem() {//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;

    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 package cn.riddles.activity;
    02  
    03 import android.app.Activity;
    04 import android.os.Bundle;
    05 import android.widget.ListView;
    06  
    07 public class MainActivity extends Activity {
    08     private ListView lv;
    09     @Override
    10     public void onCreate(Bundle savedInstanceState) {
    11         super.onCreate(savedInstanceState);
    12         setContentView(R.layout.main);
    13         lv = (ListView) this.findViewById(R.id.test_lv);
    14         lv.setAdapter(new SongListAdapter(this));
    15     }
    16 }
    view sourceprint?
    01 package cn.riddles.activity;
    02  
    03 import android.content.Context;
    04 import android.util.Log;
    05 import android.view.LayoutInflater;
    06 import android.view.View;
    07 import android.view.ViewGroup;
    08 import android.widget.BaseAdapter;
    09 import android.widget.ImageView;
    10 import android.widget.TextView;
    11 /**
    12  * @author riddlezhang 歌曲条目适配器
    13  */
    14 public class SongListAdapter extends BaseAdapter {
    15     private static final String TAG = "SongListAdapter";
    16     private Context mContext;
    17     private String[] strings = {"王力宏","吴尊","何润东","金城武","吴彦祖"};
    18     private String[] 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     public SongListAdapter(Context mContext) {
    24         this.mContext = mContext;
    25     }
    26  
    27     public void setmContext(Context mContext) {
    28         this.mContext = mContext;
    29     }
    30  
    31     public int getCount() {
    32         return paths.length;
    33     }
    34  
    35     public Object getItem(int position) {
    36         return position;
    37     }
    38  
    39     public long getItemId(int position) {
    40         return position;
    41     }
    42  
    43     public View getView(int position, 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         new CanvasImageTask().execute(image);//异步加载图片
    50         Log.i(TAG, "execute:"+strings[position]);
    51         return convertView;
    52     }
    53      
    54 }
    view sourceprint?
    01 package cn.riddles.activity;
    02  
    03 import java.io.InputStream;
    04 import java.net.HttpURLConnection;
    05 import java.net.URL;
    06  
    07 import android.graphics.drawable.Drawable;
    08 import android.os.AsyncTask;
    09 import android.util.Log;
    10 import android.view.View;
    11 import android.webkit.URLUtil;
    12  
    13  
    14 /**
    15  * @author riddlezhang
    16  *  异步加载图片
    17  */
    18 public class AsyncViewTask extends AsyncTask<View, Void, Drawable>{
    19     private View mView;
    20     protected Drawable 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 = new URL(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                 return null;
    39             }
    40         }
    41         this.mView=view;
    42         return drawable;
    43     }
    44  
    45     protected void onPostExecute(Drawable drawable) {
    46         if (drawable != null) {
    47             this.mView.setBackgroundDrawable(drawable);
    48             this.mView= null;
    49         }
    50     }
    51  
    52 }
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  • 原文地址：https://www.cnblogs.com/Greenwood/p/2003170.html
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