我是Android新手，尝试使用异步任务加载一些图片并将其填充到ListView。但是对于我当前的代码，图像没有设置为正确的ImageViews，并且每当我滚动时它们都会改变。我找不到我犯的错误。提前谢谢。
public class BookAdapter extends ArrayAdapter<Book> {
public BookAdapter(Context context, ArrayList<Book> objects) {
super(context, 0, objects);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = null;
View booksView = convertView;
// inflate a view if its empty
if (booksView == null) {
holder = new ViewHolder();
booksView = LayoutInflater.from(getContext()).inflate(R.layout.list_item, parent, false);
holder.bookName = booksView.findViewById(R.id.book_name_textView);
holder.publishedDate = booksView.findViewById(R.id.dateTextView);
holder.bookAuthor = booksView.findViewById(R.id.author_textView);
holder.bookImage = booksView.findViewById(R.id.book_image);
booksView.setTag(holder);
} else {
holder = (ViewHolder) booksView.getTag();
}
Book currentBook = getItem(position);
if (holder.bookImage != null && currentBook.getBookImage()!=null) {
new LoadImages(holder.bookImage).execute(currentBook.getBookImage());
}
holder.bookName.setText(currentBook.getBookName());
holder.bookAuthor.setText(currentBook.getAuthor());
holder.publishedDate.setText(currentBook.getDate());
return booksView;
}
private class ViewHolder {
ImageView bookImage;
TextView bookName;
TextView bookAuthor;
TextView publishedDate;
}
}
将以下类用于asynctask
public class LoadImages extends AsyncTask<String,Void,Bitmap>{
private WeakReference<ImageView> imageview;
public LoadImages(ImageView imv){
imageview=new WeakReference<ImageView>(imv);
}
/** Background process
* input:url
* output: Bitmap image
* It passed into onPostExecute method
**/
@Override
protected Bitmap doInBackground(String... urls) {
return QueryUtils.fetchBookImages(urls[0]);
}
/** This method called after the doINputBackground method
* input:Bitmap image
* output: image set into the image view
* Image view passed from RecyclerViewOperation to ShowImage class through constructor
**/
@Override
protected void onPostExecute(Bitmap result) {
if((imageview!=null)&&(result!=null)){
ImageView imgview=imageview.get();
if(imgview!=null){
imgview.setImageBitmap(result);
}
}
}
}
注意： fetchBookImages类加载返回位图。