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POOnly loading and unloading data based on what's visible in a VirtualObjectListView, using ObjectListView?
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copied!<p>I'm writing a video manager in C# using <a href="http://objectlistview.sourceforge.net/cs/index.html" rel="nofollow">ObjectListView</a>, where preview images are generated, saved, and an entry is put into a sqlite db. From there, I use a VirtualObjectListView component to display the entries (Including the first image as a preview) in Details mode.</p> <p>The problem I've ran into is that with several hundred+ entries, it starts to eat up ram and I'm seeing <strong>a lot</strong> of files <em>(Lots of duplicates too)</em> open/locked in Process Explorer. So, I've attempted to implement a caching system - where only 30 images are loaded at a time, and ones not needed are unloaded while new ones are loaded.</p> <p>It doesn't work. It ends up loading multiple copies of each file somehow, and it just feels... Hacky. I've spent the past few days looking for an event or something that I can bind a method to, to do this - but I can't, so I've had to use <strong>GetNthObject</strong> in <strong>AbstractVirtualListDataSource</strong>.</p> <p>Anyways, here's my code:</p> <pre><code>public override object GetNthObject(int n) { VideoInfo p = (VideoInfo)this.Objects[n % this.Objects.Count]; p.ID = n; int storeBufferHalf = 5; int storeFrom = (n - storeBufferHalf < 0) ? 0 : n - storeBufferHalf; int storeTo = (n + storeBufferHalf >= Objects.Count()) ? Objects.Count() - 1 : n + storeBufferHalf; foreach (int cacheItem in cacheList.ToList()) { if (cacheItem >= storeFrom && cacheItem <= storeTo) continue; VideoInfo unloadItem = (VideoInfo)this.Objects[cacheItem]; //Debug.WriteLine(cacheItem + " Preparing to delete cache: " + unloadItem.Name); unloadItem.DestroyPreviewImage(); cacheList.Remove(cacheItem); } //Load up items into cache. for (int i = storeFrom; i < storeTo; i++) { if (!cacheList.Contains(i)) { VideoInfo loadItem = (VideoInfo)this.Objects[i]; if (loadItem.PreviewImage != null) continue; loadItem.SetPreviewImage(); cacheList.Add(i); } } return p; } </code></pre> <p>Some more information: Basically, it <em>kind of</em> works... It <strong>does</strong> load multiple copies of each file, it does end up loading more images than it should after you scroll down a bit (The entire test DB of 60 items, actually), BUT scrolling the list up and down a few times gets it to unload the files (At least according to Process Explorer).</p> <p>After that, it starts loading them all up again, some of them multiple times...</p>

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