Question

I have no issues invoking actions on UI controls through BeginInvoke and such, however, that’s a void method. I need to get a value from a textbox for use in a different thread.

How can I accomplish this?

Answer 1

The simplest solution is to capture a local variable in a closure.

String text;
textBox.Invoke(() => text = textBox.Text);

The compiler will generate some code that is much like chibacity’s solution – the local variable becomes a field of a compiler-generated class.

UPDATE

This does not work – the lambda expression is not assignable to Delegate. This problem can be solved using an extension method.

internal void ExecuteOnOwningThread(this Control control, Action action)
{
    if (control.InvokeRequired)
    {
        control.Invoke(action);
    }
    else
    {
        action();
    }
}

The usage is then as follows.

String text;
textBox.ExecuteOnOwningThread(() => text = textBox.Text);

It is possible to stuff multiple statements into the lambda expression.

textBox.ExecuteOnOwningThread(() =>
{
    DoStuff();
    text = textBox.Text
    DoOtherStuff();
});

But as chibacity already mentioned in a comment it may be better to explicitly write a method. Beyond a certain point using lambda expressions will adversely affect the readability of the code. And using lambda expressions is of course very prone to introducing repeated code.