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 |
} |