使用AsyncTask for Android ListView更新图像缩略图的操作不正确 [英] updating of Image Thumbnails using AsyncTask for Android ListView not coming proper
问题描述
我从服务器收到有关数据和图像url的强烈响应.我需要在列表视图上显示它们.图片应该像缩略图一样.为了使它正确，我已经自定义了我的适配器并使用异步任务获取图像.这是我的适配器和Asynctask代码:
I am getting a big response from the server with data and image url. I need to display them on the List View. Images should be like thumbnails. To make it proper i have customized my Adapter and getting the images using Async Task. Here is my Adapter and Asynctask Code:
public class TalkofTownAdapter extends BaseAdapter{
private LayoutInflater inflater = null;
private Context context = null;
ImageView thumb_image = null;
private ProgressDialog progressbar = null;
ArrayList<String> items;
ArrayList<String> thumb_url;
public TalkofTownAdapter(Context c, ArrayList<String> list, ArrayList<String> thumb)
{
this.context = c;
this.items = list;
this.thumb_url = thumb;
progressbar = new ProgressDialog(c);
Log.d("Testing", "talk of town adapter constructor "+items.size());
inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return items.size();
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return position;
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = inflater.inflate(R.layout.talkoftown, null);
Log.d("Testing", "before creating holder object");
holder = new ViewHolder();
holder.headlineView = (TextView) convertView.findViewById(R.id.list_title);
holder.duration = (TextView)convertView.findViewById(R.id.duration);
holder.imageView = (ImageView) convertView.findViewById(R.id.list_image_playlist);
Log.d("Testing", "image view created :::::::: ");
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
Log.d("Testing", "text::: "+items.get(position));
holder.headlineView.setText(items.get(position));
Log.d("Testing", "settting the text ");
holder.duration.setText("22/09/1987");
if (holder.imageView != null) {
Log.d("Testing", "getting the image "+thumb_url.get(position));
new ImageDownloaderTask(holder.imageView).execute(thumb_url.get(position));
}
return convertView;
}
static class ViewHolder {
TextView headlineView;
TextView duration;
ImageView imageView;
}
public static Bitmap getBitmapFromURL(String src) {
try {
URL url = new URL(src);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setDoInput(true);
connection.connect();
InputStream input = connection.getInputStream();
Bitmap myBitmap = BitmapFactory.decodeStream(input);
Log.d("Testing", "image loaded "+myBitmap);
// myBitmap = Bitmap.createBitmap(100, 50, Config.ARGB_8888);
myBitmap = Bitmap.createScaledBitmap(myBitmap,(int)(myBitmap.getWidth()), (int)(myBitmap.getHeight()), true);
return myBitmap;
} catch (IOException e) {
Log.d("Testing", "exception is getting the image "+e.toString());
e.printStackTrace();
return null;
}
}
public void startProgress()
{
progressbar.setMessage("Please wait");
progressbar.show();
}
public void stopProgress()
{
progressbar.dismiss();
}
class ImageDownloaderTask extends AsyncTask<String, Void, Bitmap> {
private final WeakReference<ImageView> imageViewReference;
public ImageDownloaderTask(ImageView imageView) {
imageViewReference = new WeakReference<ImageView>(imageView);
}
@Override
// Actual download method, run in the task thread
protected Bitmap doInBackground(String... params) {
// params comes from the execute() call: params[0] is the url.
return getBitmapFromURL(params[0]);
}
@Override
// Once the image is downloaded, associates it to the imageView
protected void onPostExecute(Bitmap bitmap) {
if (isCancelled()) {
bitmap = null;
}
if (imageViewReference != null) {
ImageView imageView = imageViewReference.get();
if (imageView != null) {
if (bitmap != null) {
imageView.setImageBitmap(bitmap);
} else {
imageView.setImageDrawable(imageView.getContext().getResources()
.getDrawable(R.drawable.rihanna));
}
}
}
}
}
现在，缩略图将显示为默认图像，然后随下载的图像一起更改.但是，如果我向下滚动列表视图，则图像会不断变化，并且出现在上面已经向上滚动的行中的图像重复出现.所以在这里我要说的是，图像按相应行的正确顺序排列.我知道这里也有很多教程和质量检查.但是我尝试了很多解决方案，但无法正常工作.
Now the thumbnails are showing with the default image and then changing with downloaded images. But if i am scrolling down the list view, images are keep on changing and coming duplicates of those that appeared in the rows above that were already scrolled up. So i mean to say here, the images are coming on proper order for the corresponding rows. I know there are lots of tutorials and QA here also. But i have tried lots of solutions and it did not work properly.
有人可以帮我吗?
推荐答案
问题在于您是否符合条件.只需删除条件条件if (holder.imageView != null) {，问题就出在每一次getView都会检查您的视图是否为空，并以此为基础执行并膨胀图像.
The problem is with you if condition. Just remove the if condition if (holder.imageView != null) { the problem is each and everytime getView will check for your view is null or not and based on that it will execute and inflate the image.
更改您的if条件，例如
Change your if condition like
if(thumb_url.get(position) !=null)
{
Log.d("Testing", "getting the image "+thumb_url.get(position));
new ImageDownloaderTask(holder.imageView).execute(thumb_url.get(position));
}
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