CODEWITHSUNDEEP
c#winformsmultithreadinguser-interface
Ryan
Ryan

Reputation: 877

Clarification on updating GUI from a separate Thread using an anonymous method

I've found what looks like a very simple solution to my current situation.

My current situation is that I want to do some I/O-heavy operations on a new Thread, so that I do not bog down my GUI Thread. I have a function written, as a member of my Form, that does these I/O operations already, but running it on the GUI Thread really makes the application a pain to use. So my plan was to just run this function in a new Thread. So, I created a Thread variable, in my form, and am trying to get it to use that function as the ThreadStart parameter. It does not seem to like it, though.

I found an elegant looking solution, as a response to another thread, here.

///...blah blah updating files
string newText = "abc"; // running on worker thread
this.Invoke((MethodInvoker)delegate {
    someLabel.Text = newText; // runs on UI thread
});
///...blah blah more updating files

From the looks of that response, I could run this function in a new Thread and then use an anonymous function to update my Form when the Thread has finished its calculations. I'm just not good enough to fill in the blanks from that response, though.

Everything I seem to read about Threads says that my ThreadStart function needs to be a static method in a new class. That response seems to suggest that I can do it within my Form class though, so that the this reference still references my Form instance. Otherwise, if my ThreadStart parameter were a different class, I'd have to pass in references to the Form instance, and that seems like more code, right?

Would anybody mind helping me fill in the context for that response? Thanks in advance!

Upvotes: 2

Views: 868

Answers (1)

Servy
Servy

Reputation: 203825

There are a lot of ways you can do this. A very simple, straightforward one that's been around for a number of versions is to use the BackgroundWorker. It is designed for exactly this case. It has a DoWork method that runs in a background thread, and a Completed event that is fired after the work is done which runs in the UI thread (so you don't need to call invoke or anything to update the UI with the results). It even has support built in for reporting progress (the report progress event also runs in the UI thread) so you can easily update a progress bar or status text.

MSDN has some examples as well, and you can find lots more through some simple searches.

Another option, made available through C# 4.0, is to use Tasks. You can start a new task which will be run in a background thread, and then you can add a continuation which will be in the UI thread.

Here is a simple example:

private void button1_Click(object sender, EventArgs e)
{
    Task.Factory.StartNew(() => doStuffInBackground())
        .ContinueWith(task => updateUI(), TaskScheduler.FromCurrentSynchronizationContext());
}

private void updateUI()
{
    throw new NotImplementedException();
}

private void doStuffInBackground()
{
    throw new NotImplementedException();
}

You can of course do whatever you want in the actual lambdas that I have there, or you could even remove the lambdas and put methods in there directly as long as you ensure the signatures are correct. You could also continue chaining these continuations if you wanted, allowing you to, for example, to task 1, update a label, then do task 2, update a label, etc. The main disadvantage is that it's not good at updating a progress bar frequently inside of a loop, the way a BackgroundWorker can.

Upvotes: 1

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