ListView_SelectedIndexChanged event

Question

I have a listview which can contain a large number of items (files, sizes are included) and in the status bar of the application I show how many items are selected and the total number of bytes of all the selected files. I have a handle set up for ListView_SelectedIndexChanged to caluculate this information and place it on the statusbar. At first my "Select All" was pretty slow as it looped through the items in the ListView and set them to selected one at a time which called my selected index changed event (once for each time an item was selected) and calculated the total. I solved this problem by having my select all function -= the event handler before it started and then re-adding it and then manaually calling it when it was done selecting everything. That worked great, but now my problem is whenever I have everything selected and then select one item the framework calls the ListView_SelectedIndexChanged once for every item it deselects. And this is slowwwww. Does anyone have an idea about how I fix this up?

Administrator · Answer

Basically I've got a situation where the framework fires off an event 1000's of times and I really only need to handle the last one it fires. Example: ListView has 2000 items selected User selects one item item (which deselects 1999 items) Frameworks calls my ListView_SelectedIndexChanged event 1999 times In this even I do some intense processing and if I have to do this processing 1999 times the user gets to wait about 40 seconds for those 1999 items to deselect. The only way I could think of to do it with threads so far is to have a thread which does the calculations and then the even would try to call the thread but don't if it's already running the calculation. That almost works but I need to do the calculations once more at the end when the last ListView_SelectedIndexChanged event is called. Not sure how I'd handle that. Threads are also not my strong suit (as is probably obvious from the above)

Administrator · Answer

As I understand You want to lock variable until all computations will be done? I'm not good in threads. May be the other solution is to check at beginning of computations if some operations are waiting and in this case not to compute?

Administrator · Answer

I changed it to a 10th of a second so it's pretty snappy but if there is a better way to do what I was looking for I'm open to give it a shot. So how would say would be a good way to do it using threads as opposed to timers?

Administrator · Answer

Personally I prefer not to use timers. Overall they are an easy solution but may not be the most efficient (although waiting half a second for processing isn't bad). I generally like to use threads. Most of my programs are multi-threaded for just this kind of application. You simply perform a lock on the variable you are currently handling and then the other threads can't access it until you are done.

Administrator · Answer

Wow that worked like a charm. Time to go read up on that class and find out why now and see if there are any other clever applications for the thing. Thanks!

Administrator · Answer

Try to use timer to delay calculations. It's dummy but works: private System.Timers.Timer tmOkres; this.tmOkres.AutoReset = false; this.tmOkres.Interval = 1000; this.tmOkres.SynchronizingObject = this; this.tmOkres.Elapsed += new System.Timers.ElapsedEventHandler(this.tmOkres_Elapsed); private void ListView_SelectedIndexChanged(...) { this.tmOkres.Stop(); this.tmOkres.Start(); } private void tmOkres_Elapsed(object sender System.Timers.ElapsedEventArgs e) { this.tmOkres.Stop(); ... //calculations ... }