我知道这个问题被多次询问..
但是我无法得到任何正确的解决方案。在我的应用程序中，我使用AsyncTask来加载图像。
我使用AsyncTask因为我想要平滑滚动listview ..并且在实现AsyncTask之后我的listView顺利滚动..
但现在问题是图像在滚动后正在改变.. 。
我该怎么办？
MyAdapter班级
package com.example.adapter;
public class DisplayAllFeedAdapter extends ArrayAdapter<DisplayAllFeedItem> {
private final List<DisplayAllFeedItem> list;
private final Activity context;
ExifInterface exif;
public DisplayAllFeedAdapter(Activity context, List<DisplayAllFeedItem> list) {
super(context, R.layout.feed_screen, list);
this.context = context;
this.list = list;
}
static class ViewHolder {
public TextView optionalDesc, reportedBy;
public LinearLayout layout;
public ImageView displayFeedimg, channelIcon;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder viewHolder = null;
if (convertView == null) {
LayoutInflater inflater = context.getLayoutInflater();
convertView = inflater.inflate(R.layout.display_all_feed_listitem, null);
viewHolder = new ViewHolder();
viewHolder.optionalDesc = (TextView) convertView.findViewById(R.id.txtFeedOptionalDesc);
viewHolder.reportedBy = (TextView) convertView.findViewById(R.id.txtFeedReportedBy);
viewHolder.displayFeedimg = (ImageView) convertView
.findViewById(R.id.imgFeedDisplayImage);
viewHolder.layout = (LinearLayout) convertView.findViewById(R.id.layoutChannelImgView);
convertView.setTag(viewHolder);
convertView.setTag(R.id.txtFeedOptionalDesc, viewHolder.optionalDesc);
convertView.setTag(R.id.txtFeedReportedBy, viewHolder.reportedBy);
convertView.setTag(R.id.imgFeedDisplayImage, viewHolder.displayFeedimg);
convertView.setTag(R.id.layoutChannelImgView, viewHolder.layout);
} else {
viewHolder = (ViewHolder) convertView.getTag();
}
String temp;
String drawableImagePath = list.get(position).getMediaChannelName();
List<String> channelList = new ArrayList<String>();
while (drawableImagePath.length() > 0) {
if (drawableImagePath.indexOf(",") == -1) {
temp = drawableImagePath.substring(0);
channelList.add(temp);
break;
} else {
temp = drawableImagePath.substring(0, drawableImagePath.indexOf(","));
}
channelList.add(temp);
drawableImagePath = drawableImagePath.substring(drawableImagePath.indexOf(",") + 1);
}
viewHolder.layout.removeAllViews();
for (int i = 0; i < channelList.size(); i++) {
LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(dpToPx(30),
dpToPx(30));
ImageView imageView = new ImageView(context);
layoutParams.setMargins(0, 0, 10, 0);
imageView.setLayoutParams(layoutParams);
imageView.setImageResource(Integer.parseInt(channelList.get(i)));
viewHolder.layout.addView(imageView);
}
String tempPath = list.get(position).getMediaPath();
File mediaFile = new File(tempPath);
Bitmap bitmap;
viewHolder.optionalDesc.setText(list.get(position).getMediaDesc());
viewHolder.reportedBy.setText("Reported By " + list.get(position).getMediaDisplayName());
if (viewHolder != null) {
new LoadImage(viewHolder).execute(tempPath);
}
return convertView;
}
private class LoadImage extends AsyncTask<String, String, Bitmap> {
// File mediaFile = new File(tempPath);
Bitmap bitmap, displayBitmap;
File mediaFile;
String mediaPath;
private final ViewHolder imageViewReference;
public LoadImage(ViewHolder viewHolder) {
imageViewReference = viewHolder;
}
@Override
protected Bitmap doInBackground(String... params) {
// File f = new File(params[0]);
mediaPath = params[0];
mediaFile = new File(mediaPath);
if (mediaFile.exists()) {
if (isImage(mediaPath)) {
Bitmap myBitmap = BitmapFactory.decodeFile(mediaFile.getAbsolutePath());
int height = (myBitmap.getHeight() * 512 / myBitmap.getWidth());
Bitmap scale = Bitmap.createScaledBitmap(myBitmap, 512, height, true);
int rotate = 0;
try {
exif = new ExifInterface(mediaFile.getAbsolutePath());
} catch (IOException e) {
e.printStackTrace();
}
int orientation = exif.getAttributeInt(ExifInterface.TAG_ORIENTATION,
ExifInterface.ORIENTATION_UNDEFINED);
switch (orientation) {
case ExifInterface.ORIENTATION_NORMAL:
rotate = 0;
break;
case ExifInterface.ORIENTATION_ROTATE_270:
rotate = 270;
break;
case ExifInterface.ORIENTATION_ROTATE_180:
rotate = 180;
break;
case ExifInterface.ORIENTATION_ROTATE_90:
rotate = 90;
break;
}
Matrix matrix = new Matrix();
matrix.postRotate(rotate);
displayBitmap = Bitmap.createBitmap(scale, 0, 0, scale.getWidth(),
scale.getHeight(), matrix, true);
} else {
displayBitmap = ThumbnailUtils.createVideoThumbnail(mediaPath,
Thumbnails.MICRO_KIND);
}
}
return displayBitmap;
}
@Override
protected void onPostExecute(Bitmap result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
if (imageViewReference != null) {
imageViewReference.displayFeedimg.setImageBitmap(result);
}
// tempView.displayFeedimg.setImageBitmap(result);
}
}
public int dpToPx(int dp) {
DisplayMetrics displayMetrics = getContext().getResources().getDisplayMetrics();
int px = Math.round(dp * (displayMetrics.xdpi / DisplayMetrics.DENSITY_DEFAULT));
return px;
}
public static boolean isImage(String str) {
boolean temp = false;
String[] arr = { ".jpeg", ".jpg", ".png", ".bmp", ".gif" };
for (int i = 0; i < arr.length; i++) {
temp = str.endsWith(arr[i]);
if (temp) {
break;
}
}
return temp;
}
}
答案 0 :(得分：0)
我不清楚您的问题（需要更好的澄清），但我知道在加载图像时存在性能滞后的问题。
请查看Google的网络Making a Standard Request。 搜索（通用）图像加载器，文本“使用ImageLoader和NetworkImageView”。 您可以通过位于该文本下方的缓存来进一步提高性能。
网页上的代码段：
ImageLoader mImageLoader;
ImageView mImageView;
// The URL for the image that is being loaded.
private static final String IMAGE_URL =
"http://developer.android.com/images/training/system-ui.png";
...
mImageView = (ImageView) findViewById(R.id.regularImageView);
// Get the ImageLoader through your singleton class.
mImageLoader = MySingleton.getInstance(this).getImageLoader();
mImageLoader.get(IMAGE_URL, ImageLoader.getImageListener(mImageView,
R.drawable.def_image, R.drawable.err_image));
知识渊博的作者在Solving the Android image loading problem...中似乎有一个很好的教程。 玩得开心。总有一天我可能也要解决这个问题。请告诉我们。
答案 1 :(得分：0)
除了我之前的回答，还有另一种可能的解决方案。但它与谷歌的推荐有所不同，所以要小心......
查看Stackoverflow讨论ListView like in universal image loader sample app。该页面中的结帐代码。在CarListAdapter中：
ImageLoader = ImageLoader.getInstance();
imageLoader.init(ImageLoaderConfiguration.createDefault(context));
......在另一种方法中：
imageLoader.displayImage(...);
我的两个答案都导致了一点，使用（通用）图像加载器。