滚动时，Android listview图像消失
当滚动我的列表视图与图像。 图像将消失，然后在一两秒后重新出现。 任何关于此事的帮助将不胜感激！
这是在我的getView中调用下面的代码：
image_main.setImageBitmap(null);
if (curr == 0 && image != null) {
list_image.setVisibility(View.VISIBLE);
image_preference = preferences.getString("image_preferences", "false");
time_right.setVisibility(View.GONE);
if (image_preference.equals("false")) {
ImageDownloader imgDwn = new ImageDownloader();
imgDwn.download(image, image_main, image_table);
}
我的代码：
public class ImageDownloader {
public void download(String url, ImageView imageView, TableLayout imageTable) {
if (cancelPotentialDownload(url, imageView)) {
BitmapDownloaderTask task = new BitmapDownloaderTask(imageView, imageTable);
DownloadedDrawable downloadedDrawable = new DownloadedDrawable(task);
imageView.setImageDrawable(downloadedDrawable);
task.execute(url);
}
}
class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> {
String url;
private final WeakReference<ImageView> imageViewReference;
private final WeakReference<TableLayout> imageTableReference;
public BitmapDownloaderTask(ImageView imageView, TableLayout imageTable) {
imageViewReference = new WeakReference<ImageView>(imageView);
imageTableReference = new WeakReference<TableLayout>(imageTable);
}
@Override
protected Bitmap doInBackground(String... params) {
BitmapFactory.Options o = new BitmapFactory.Options();
o.inJustDecodeBounds = true;
BitmapFactory.decodeFile(params[0], o);
final int REQUIRED_SIZE=70;
//Find the correct scale value. It should be the power of 2.
int width_tmp=o.outWidth, height_tmp=o.outHeight;
int scale=4;
while(true){
if(width_tmp/2<REQUIRED_SIZE || height_tmp/2<REQUIRED_SIZE)
break;
width_tmp/=2;
height_tmp/=2;
scale++;
}
//Decode with inSampleSize
BitmapFactory.Options o2 = new BitmapFactory.Options();
o2.inSampleSize=scale;
return BitmapFactory.decodeFile(params[0], o2);
}
@Override
protected void onPostExecute(Bitmap result) {
if (isCancelled()) {
result = null;
}
if (imageViewReference != null) {
ImageView imageView = imageViewReference.get();
TableLayout imageTable = imageTableReference.get();
BitmapDownloaderTask bitmapDownloaderTask = ImageDownloader.getBitmapDownloaderTask(imageView);
// Change bitmap only if this process is still associated with it
if (this == bitmapDownloaderTask) {
imageView.setImageBitmap(result);
imageView.setVisibility(View.VISIBLE);
imageTable.setVisibility(View.VISIBLE);
}
}
}
}
static class DownloadedDrawable extends ColorDrawable {
private final WeakReference<BitmapDownloaderTask> bitmapDownloaderTaskReference;
public DownloadedDrawable(BitmapDownloaderTask bitmapDownloaderTask) {
super(Color.BLACK);
bitmapDownloaderTaskReference =
new WeakReference<BitmapDownloaderTask>(bitmapDownloaderTask);
}
public BitmapDownloaderTask getBitmapDownloaderTask() {
return bitmapDownloaderTaskReference.get();
}
}
private static boolean cancelPotentialDownload(String url, ImageView imageView) {
BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView);
if (bitmapDownloaderTask != null) {
String bitmapUrl = bitmapDownloaderTask.url;
if ((bitmapUrl == null) || (!bitmapUrl.equals(url))) {
bitmapDownloaderTask.cancel(true);
} else {
// The same URL is already being downloaded.
return false;
}
}
return true;
}
private static BitmapDownloaderTask getBitmapDownloaderTask(ImageView imageView) {
if (imageView != null) {
Drawable drawable = imageView.getDrawable();
if (drawable instanceof DownloadedDrawable) {
DownloadedDrawable downloadedDrawable = (DownloadedDrawable)drawable;
return downloadedDrawable.getBitmapDownloaderTask();
}
}
return null;
}
}
通过阅读这个问题，我发现了这个问题。 如果你隐藏了一些元素，那么你必须再次展示它们:)简单。
就您的代码而言，保持良好的状态，无论何时滚动浏览列表视图，您都会从所需的服务器每次下载图像。 一个位图缓存实现可能可以解决您的问题。
链接地址: http://www.djcxy.com/p/49429.html