Trying to use task.factory on a method

Jason

I'm trying to keep the main UI from locking up while I do a DB lookup in the background. I'm assuming this can be done with threading. I tried this Task.Factory.StartNew(()=>Method(string,string,string) but I get a message about crossthreading because the method is getting the value of a combo box. How do I avoid this?

5 Replies

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Sam Hobbs15y ago
In Windows Forms the easiest way is to use BackgroundWorker Class; it is designed for this purpose. Look for articles in this web site about it. Using that class, the BackgroundWorker.ProgressChanged Event will automatically solve the cross-threading problem. The BackgroundWorker.DoWork Event is the other thread; everything else automatically executes in the thread that creates the BackgroundWorker.
Jason15y ago
Yeah, I ran stopwatch on my parallel task and there was no difference in timing. Not sure why, maybe whatever controls the queries can't do parallel. I'll try your suggestion for the combo box though!
Vulpes15y ago
Basically, it's just the statement in which the control is accessed that needs to be marshalled back to the UI thread.

I'd do it like this:

void Method(string, string)
{
string value = null;

this.BeginInvoke(new MethodInvoker(delegate()
{
value = cmb1.SelectedItem.ToString();
}));

if (value == "Stuff")
{
// Do Stuff here
}
}

On the second point, you could use a lambda to call the existing method:

Parallel.Invoke(() => ExistingMethod());

However, I doubt whether it would parallelize correctly as I suspect it just parallelizes the various Action delegates, not what's inside them.
Jason15y ago
Do I replace the Task.Factory with the BeginInvoke? Here's a snippet. Where would I add your example?

if...
{
   Method(string,string)
}

I changed it to

if...
{
     Task.Factory.StartNew(()=>Method(string,string));
}}
Method(string, string)
{
        if(cmb1.SelectedItem.ToString() == "Stuff")
               Do stuff here

}

Also on a different note I used Parallel.Invoke() successfully but is there a way to do parallel without making a bunch of methods? I had a list of combo boxes that set datasources from queries I pulled them out of the main method and made a new method for each one, that works but is there a way to do it without making the new methods?
Vulpes15y ago
You'll need to marshal any code which accesses controls back to the UI thread to avoid the cross-threading errors. It can be done asynchronously like this:

this.BeginInvoke(new MethodInvoker(delegate()
{
// code to get combobox value
}));