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c#multithreadingthread-safetyinvoke
nitrkli
nitrkli

Reputation: 369

How to read combobox from a thread other than the thread it was created on?

I am trying to read a combobox.Text from a thread other than the thread it was created on but I am getting the error:

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Windows.Forms.dll

Additional information: Cross-thread operation not valid: Control 'levelsComboBox' accessed from a thread other than the thread it was created on.

I have used .Invoke before but only to set properties, how can I use it to read combobox.Text? Because .Invoke returns void and I need a string. Or is there another way to do it without the Invoke?

Upvotes: 30

Views: 34695

Answers (4)

Igor Vaschuk
Igor Vaschuk

Reputation: 2924

Shortest way is:

string text;
this.Invoke(() => text = combobox.Text);

Upvotes: 5

BrandonZeider
BrandonZeider

Reputation: 8152

You can do it like this:

this.Invoke((MethodInvoker)delegate()
    {
        text = combobox.Text;
    });

Upvotes: 52

João Angelo
João Angelo

Reputation: 57718

You can still use Invoke and read it to a local variable.

Something like this:

string text;

this.Invoke(new MethodInvoker(delegate() { text = combobox.Text; }));

Since Invoke is synchronous you have the guarantee that text variable will contain the value of the combo box text after it returns.

Upvotes: 18

Morten Mertner
Morten Mertner

Reputation: 9474

The easiest solution is to use the BackgroundWorker class to execute work on another thread, while still being able to update the UI (e.g. when reporting progress or when the task has completed).

Upvotes: 3

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