listView优化，是否滑动，第一行，最后一行判断，判断何时要加载图片

listView.setOnScrollListener(new OnScrollListener() {

private boolean isFling;
private boolean isLastRow;
private boolean isTop;

@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
isFling=(scrollState == OnScrollListener.SCROLL_STATE_FLING);
if (!isLastRow&&!isTop && isFling) {
adapter.setLoading(false);//不加载图片
}else
adapter.setLoading(true);//加载图片
}

@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {

//判断是否滚到第一行
if (totalItemCount>0) {
if (firstVisibleItem == 0) {
isTop = true;
}else {
isTop = false;
}

}
//判断是否滚到最后一行
if (firstVisibleItem + visibleItemCount == totalItemCount && totalItemCount > 0) {
isLastRow = true;
}else {
isLastRow = false;
}
}
});

//adapter部分代码
private boolean isLoading=true;

public void setLoading(boolean isLoading) {
this.isLoading = isLoading;
this.notifyDataSetChanged();
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ListViewHolder viewHolder=null;
if (convertView==null)
{
viewHolder=new ListViewHolder();
convertView=View.inflate(context, R.layout.base_list_item, null);
viewHolder.tvTitle=(TextView) convertView.findViewById(R.id.tv_base_list_title);
viewHolder.tvTime=(TextView) convertView.findViewById(R.id.tv_base_list_time);
viewHolder.ivMsg=(ImageView) convertView.findViewById(R.id.iv_base_list_item);
convertView.setTag(viewHolder);
}else
{
viewHolder=(ListViewHolder) convertView.getTag();
}

Log.i("ListItemAdapter", "type:"+type);

InfoNews infoNews = ((InfoNews)list.get(position));
viewHolder.tvTitle.setText(infoNews.getTit());
String src = infoNews.getSrc();
if (src==null) {
src="";
}
viewHolder.tvTime.setText(infoNews.getAddDate()+" "+src);
String path =infoNews.getImageUrl();
if(isLoading){

viewHolder.ivMsg.setTag(path);
Bitmap bm = loader.loadImage(path, 1);//异步加载图片
if (bm != null) {
viewHolder.ivMsg.setImageBitmap(bm);
} else {
viewHolder.ivMsg
.setImageResource(R.drawable.full_opacity);
}

} else{
viewHolder.ivMsg.setTag("abc");
viewHolder.ivMsg.setImageResource(R.drawable.full_opacity);
}
return convertView;
}
class ListViewHolder
{
TextView tvTitle;
TextView tvTime;
ImageView ivMsg;

}

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.BitmapFactory;
import android.graphics.BitmapFactory.Options;
import android.util.Log;

public class BitmapUtils {

/* 下载图片的方法 */
public static Bitmap Downloadpic(String Url,int type) throws Exception{
try {

URL url = new URL(Url);
//URL url = new URL("http://e.hiphotos.baidu.com/image/w%3D2048/sign=f4ac7fda33adcbef0134790698972edd/3b292df5e0fe9925983f2f4e36a85edf8db171f8.jpg");
HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
httpConn.setReadTimeout(20000);
httpConn.setConnectTimeout(20000);
InputStream input = httpConn.getInputStream();
Bitmap bit = BitmapFactory.decodeStream(input);
input.close();

FileOutputStream b = null;
//
String name = Url.substring(Url.lastIndexOf("/"));
String fileName = "/sdcard/dxt/image/"+name ;
File file = new File(fileName);
save(bit, file,type);

return bit;

} catch (IOException e) {

// TODO Auto-generated catch block

throw new Exception(e.getMessage());

}

}

/**
*
* @param data
* @param width
* @param height
* @return
*/
public static Bitmap loadBitmap(byte[] data, int width, int height) {
Options opts = new Options();
opts.inJustDecodeBounds = true;
BitmapFactory.decodeByteArray(data, 0, data.length, opts);
int xScale = opts.outWidth / width;
int yScale = opts.outHeight / height;
opts.inSampleSize = xScale > yScale ? xScale : yScale;
opts.inJustDecodeBounds = false;
Bitmap bit = BitmapFactory.decodeByteArray(data, 0, data.length, opts);
return bit;
}

/**
*
* @param path
* @return
*/
public static Bitmap loadBitmap(String path) {
return BitmapFactory.decodeFile(path);
}

/**
*
* @param bm
* @param file
*/
public static void save(Bitmap bm, File file,int type) throws IOException {
Log.i("dxt", "save bm:"+file.getName());
if (!file.getParentFile().exists()) {
file.getParentFile().mkdirs();
}
if (!file.exists()) {
file.createNewFile();
}

FileOutputStream out = new FileOutputStream(file);
if (type ==1 ) {
bm.compress(CompressFormat.JPEG, 10, out);
}else {

bm.compress(CompressFormat.JPEG, 100, out);
}
out.close();
}
}

import java.io.File;
import java.io.IOException;
import java.lang.ref.SoftReference;
import java.util.ArrayList;
import java.util.HashMap;

import org.apache.http.HttpEntity;

import android.content.Context;
import android.graphics.Bitmap;
import android.os.Handler;
import android.os.Message;
import android.util.Log;

import com.ywtx.dxt.util.BitmapUtils;
import com.ywtx.dxt.util.HttpService;

public class AsyncImageLoader {
private Context context;
private boolean isLoop;
private ArrayList<ImageLoadTask> tasks;
private Thread workThread;
private Handler handler;
private HashMap<String, SoftReference<Bitmap>> caches;

public AsyncImageLoader(final Context context, final Callback callback) {
this.context = context;
this.isLoop = true;
this.tasks = new ArrayList<AsyncImageLoader.ImageLoadTask>();
this.caches = new HashMap<String, SoftReference<Bitmap>>();
this.handler = new Handler() {
public void handleMessage(android.os.Message msg) {
ImageLoadTask task = (ImageLoadTask) msg.obj;
callback.imageLoaded(task.path, task.bitmap,task.type);
};
};
this.workThread = new Thread() {
@Override
public void run() {
while (isLoop) {
while (isLoop && !tasks.isEmpty()) {
try {
ImageLoadTask task = tasks.remove(0);
try {
Log.i("dxt", "runtask.path = "+task.path);
task.bitmap = BitmapUtils.Downloadpic(task.path,task.type);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();

}
Message msg = Message.obtain(handler, 0, task);
msg.sendToTarget();

caches.put(task.path, new SoftReference<Bitmap>(task.bitmap));
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

if (!isLoop)
break;

synchronized (this) {
try {
this.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}

};
this.workThread.start();
}

public Bitmap loadImage(String path,int type) {
if (caches.containsKey(path)) {
Log.i("dxt", path+"缓存");
Bitmap bm = caches.get(path).get();
if (bm != null) {
return bm;
}
}
File dir = context.getCacheDir();
File file = new File(dir, path);
if (file.exists()) {
Log.i("dxt", path+"SD卡");
Bitmap bm = BitmapUtils.loadBitmap(file.getAbsolutePath());
if (bm != null) {
return bm;
}
}
ImageLoadTask task = new ImageLoadTask();
task.path = path;
task.type = type;
if (!tasks.contains(task)) {
Log.i("dxt", path+"download");
tasks.add(task);
synchronized (workThread) {
try {
workThread.notify();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
return null;
}

public void quit() {
isLoop = false;
synchronized (workThread) {
workThread.notify();
}
}

private class ImageLoadTask {
private String path;
private Bitmap bitmap;
private int type;

@Override
public boolean equals(Object o) {
ImageLoadTask task = (ImageLoadTask) o;
if (path==null||task==null||task.path==null) {
return false;
}
return path.equals(task.path);
}
}

public interface Callback {
void imageLoaded(String path, Bitmap bitmap, int type);
}
}