为什么我的药滑动之后才加载图片啊
就是点开程序他不加载图片，显示的是系统图片，要往下滑才能加载，应该不是网络原因，因为没加缓存之前好像没这个问题、
5 回答
解决办法：将mImageView和mUrl声明在AsyncTask中，删除在ImageLorder中的声明。老师在ImageLorder中声明是为了Handler使用，我们这里将Handler的内容全部删除其实是没有影响的。
原理：如果我们在adapter构造方法中初始化ImageView，全局只有一个ImageLorder，而在ImageLoder中声明mImageView和mUrl，那么adapter没调用一次ShowImageByAsynctask，mImageViedw和mUrl就会被初始化一次，导致上一个bitmap形成后需要赋值的ImageVIew却发生了改变，无法加载成功。
解决办法：
1:getview()方法每次都new ImageLorder 不推荐
2:adapter构造方法中初始化ImageLorder,但是mImageView和mUrl在Asynctask中声明，避免被覆盖
但是我的监听器里面还没写函数额
package com.example.newapplication;
import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Handler;
import android.os.Message;
import android.support.v4.util.LruCache;
import android.widget.ImageView;
public class ImageLoader {
private ImageView mimageView;
private String murl;
private LruCache<String , Bitmap> mCache;
public ImageLoader(){
int MaxMemery = (int) Runtime.getRuntime().maxMemory(); //先获得最大内存
int cacheSize = MaxMemery/4;
mCache = new LruCache<String, Bitmap>(cacheSize){
protected int sizeOf(String key, Bitmap value) {
return value.getByteCount(); //每次把图片加入缓存时会调用 用来返回每张图片的大小
}
};
}
public void AddBitmapToCache(String url,Bitmap bitmap){
if (mCache.get(url)==null) {
mCache.put(url, bitmap);
}
}
public Bitmap getBitmapFromCache(String url){
return mCache.get(url);
}
//通过handler更新ui
private Handler handler = new Handler(){
public void handleMessage(android.os.Message msg) {
super.handleMessage(msg);
if (mimageView.getTag().equals(murl)) { //只有图片和url匹配时才设置图片 使他一一对应
mimageView.setImageBitmap((Bitmap) msg.obj);
}
};
};
public void showImageByAsyncTask(ImageView imageView, String url) {
Bitmap bitmap = getBitmapFromCache(url); // 从缓存中取出对应的图片
if (bitmap == null) { // 如果缓存中没有，那么必须下载
// imageView.setImageResource(R.drawable.ic_launcher); // 为空的时候先设置为自带图标
new NewsAsyncTask(imageView,murl).execute(url);
} else {
imageView.setImageBitmap(bitmap);
}
// new NewsAsyncTask(imageView,murl).execute(url);
}
// public void ShowImageByThread(ImageView imageView,final String url){
// mimageView = imageView;
// murl = url;
// new Thread(){
// public void run() {
// super.run();
// Bitmap bitmap = GetBitmapFromUrl(url); //通过下面的方法获取Bitmap对象 然后交给handler传给主线程更新UI
// Message message = new Message().obtain();//获得massage对象
// message.obj = bitmap;
// handler.sendMessage(message);
// }
// }.start();
// }
public Bitmap GetBitmapFromUrl(String urlString){
InputStream is = null;
try {
URL url = new URL(urlString);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection(); //获得URL之后获得连接
is = new BufferedInputStream(httpURLConnection.getInputStream());
Bitmap bitmap = BitmapFactory.decodeStream(is); //将输入流转换成Bitmap对象
httpURLConnection.disconnect();
return bitmap;
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}
private class NewsAsyncTask extends AsyncTask<String, Void, Bitmap> {
public NewsAsyncTask(ImageView imageView,String url) {
mimageView = imageView;
murl = url;
}
@Override
protected Bitmap doInBackground(String... params) {
String url = params[0];
Bitmap bitmap = GetBitmapFromUrl(url);// 从网络获取图片 前面bitmap一直没内容 现在才从网上获取资源
if (bitmap != null) {
AddBitmapToCache(url, bitmap); // 将图片加入缓存
}
return bitmap;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
super.onPostExecute(bitmap);
// ImageView imageView = (ImageView) mListView.findViewWithTag(mUrl);
// if (imageView != null && bitmap != null) {
// imageView.setImageBitmap(bitmap);
// }
// mTask.remove(this);
// if (mimageView.getTag().equals(murl)) { //前面在Myadapter里面已经将图片对应url，如果对应才设置图片
// mimageView.setImageBitmap(bitmap);
// }
if(mimageView.getTag()==null){//初始化时并未设置Tag
mimageView.setTag(murl);
}else if(mimageView.getTag().equals(murl)){//已经设置过Tag
mimageView.setImageBitmap(bitmap);
}
}
}
}
package com.example.newapplication;
import java.util.List;
import java.util.zip.Inflater;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
public class MyAdapter extends BaseAdapter{
private List<NewsBean> mList;
private LayoutInflater inflater;
private ImageLoader mimageLoader;
private int mStart,mEnd;
public static String[] URLS;
public MyAdapter(List<NewsBean> data,Context context){
mList = data;
inflater = LayoutInflater.from(context);
mimageLoader = new ImageLoader(); //初始化ImageLoader，避免后面重复创建
URLS = new String[data.size()];
for (int i = 0; i < data.size(); i++) {
URLS[i] = data.get(i).imageViewURL;
}
}
public int getCount() {
return mList.size();
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return mList.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView==null) { //如果该view对象为空 则创建 否则 直接通过Gettag()方法获得
holder = new ViewHolder();
convertView = inflater.inflate(R.layout.item_layout, null); //将显示样式转换成View对象
holder.imageView = (ImageView) convertView.findViewById(R.id.imageView1); //初始化holder的组件 find样式中的id
holder.Title = (TextView) convertView.findViewById(R.id.Item_tv1);
holder.conten = (TextView) convertView.findViewById(R.id.Item_tv2);
convertView.setTag(holder);
}else {
holder = (ViewHolder) convertView.getTag();
}
//设置控件的资源
holder.imageView.setImageResource(R.drawable.ic_launcher);
String url = mList.get(position).imageViewURL;
holder.imageView.setTag(url); //将图片和url绑定
mimageLoader.showImageByAsyncTask(holder.imageView, url); //设置图片
holder.Title.setText(mList.get(position).Title); //设置标题
holder.conten.setText(mList.get(position).content);
return convertView;
}
//通过该对象 避免重复创建View对象
class ViewHolder{
ImageView imageView;
TextView Title,conten;
}
// public void onScrollStateChanged(AbsListView view, int scrollState) {
// if (scrollState==SCROLL_STATE_IDLE) { //表示此时滑动在停止状态
//
// }
// }
// @Override
// public void onScroll(AbsListView view, int firstVisibleItem,
// int visibleItemCount, int totalItemCount) {
// mStart = firstVisibleItem;
// mEnd = firstVisibleItem+visibleItemCount;
// }
}
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