总体框架：
1.滚动加载
//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
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
}
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。
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 |
} |
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", |
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 |
} |
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 |
} |