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POIssue when fast scroll a listview?
 

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  1. POIssue when fast scroll a listview?
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    <p>I am working on a small project where I create a <code>listview</code> bound to an ArrayAdapter. In the <code>getView()</code> function of ArrayAdapter, I do a loading of images from web <code>urls</code> on thread, and set them to list items(based on position off course, so <code>url[0]</code> image is set to <code>list_item[0]</code> etc). It all seems to work well.</p> <p>However when I was testing the app, I noticed that if I wait my listview to fully display, then perform a fast scroll back and forth, I see sometimes <strong>the image on one list item is misplaced on other</strong>(like being in an intermediate state). However it's not going away until i scroll the wrongly-displayed-item out of screen and then back.</p> <p>Has anyone met this kind of problem before? I do not know if it relates to my loading web <code>url</code> using thread, or maybe loading image from local resource folder can have the same issue.</p> <p>This actually leads to a question i have about <code>getView()</code> function. I think the logic is correct in my <code>getView()</code> 'cause it's as simple as a binding of url to view based on position. And whenever <code>getView()</code> get a chance to be called, like when I scroll an item out of screen then back, it will make the list item display correctly.</p> <p>The thing I do not get is how to explain the issue that happened(like an intermediate state), and how to avoid it when writing code?</p> <p>Any one could help?</p> <p>I paste my adapter code piece below, but i think the question maybe a general one:</p> <pre><code> @Override public View getView(int position, View v, ViewGroup parent) { ViewHolder viewHolder = null; if (v == null) { LayoutInflater inflater = (LayoutInflater) getContext() .getSystemService(Context.LAYOUT_INFLATER_SERVICE); v = inflater.inflate(layoutResourceId, parent, false); viewHolder = new ViewHolder(); viewHolder.title = (TextView) v.findViewById(R.id.title); viewHolder.description = (TextView) v.findViewById(R.id.description); viewHolder.image = (ImageView) v.findViewById(R.id.image); v.setTag(viewHolder); } else { viewHolder = (ViewHolder) v.getTag(); } listItem item = items[position]; //items is some global array //passed in to ArrayAdapter constructor if (item != null) { viewHolder.title.setText(item.title); viewHolder.description.setText(item.description); if (!(item.imageHref).equalsIgnoreCase("null")) { mDrawableManager.fetchDrawableOnThread(item.imageHref, viewHolder.image); } else { viewHolder.image.setImageDrawable(null); } } return v; } } static class ViewHolder { TextView title; TextView description; ImageView image; } </code></pre>
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    1. USRathakrishnan
    1. USuser1559625
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    1. COTry making method fetchDrawableOnThread() as synchronized. It worked for me. I struggled with this problem for 4 months.
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      1. USYogesh Somani
    2. COThanks a lot Yogesh! Synchronization, synchronization, synchronization. I think you're right in that the mDrawableManager i used has a hashmap that's accessed by multiple threads. And it looks a lot better.
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    3. COSo shall I write it as an answer. Will you accept it?
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      1. USYogesh Somani
 

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