WPF invoke a control

c# wpf invoke

47,060

When you call Invoke, you're not specifying your argument (text). When the Dispatcher tries to run your method, it doesn't have a parameter to supply, and you get an exception.

Try:

this.textboxlink.Dispatcher.Invoke(
     System.Windows.Threading.DispatcherPriority.Normal,
     new TBXTextChanger(this.WriteToTextBox), text);

If you want to read the value from a text box, one option is to use a lambda:

string textBoxValue = string.Empty;

this.textboxlink.Dispatcher.Invoke(DispatcherPriority.Normal, 
     new Action( () => { textBoxValue = this.textboxlink.Text; } ));

if (textBoxValue == string.Empty)
    Thread.Sleep(5000);

47,060

Author by

Yustme

Updated on April 16, 2020

Comments

Yustme about 4 years
How can I invoke a control with parameters? I've googled this up, but nowhere to find!

invoke ui thread

This is the error i get:

Additional information: Parameter count mismatch.

And this happens when i do a simple check whether the text property of a textbox control is empty or not. This works in WinForms:
```
if (this.textboxlink.Text == string.Empty)
   SleepThreadThatIsntNavigating(5000);
```
It jumps from this if the line to the catch block and shows me that message.

This is how i try to invoke the control:
```
// the delegate:
private delegate void TBXTextChanger(string text);

private void WriteToTextBox(string text)
{
    if (this.textboxlink.Dispatcher.CheckAccess())
    {
        this.textboxlink.Text = text;
    }
    else
    {
        this.textboxlink.Dispatcher.Invoke(
            System.Windows.Threading.DispatcherPriority.Normal,
            new TBXTextChanger(this.WriteToTextBox));
    }
}
```
What am I doing wrong? And since when do i have to invoke a control when i just want to read its content?
Yustme over 13 years

Ok, i fixed that, that was my first question. But how do i read the content of a textbox?
Reed Copsey over 13 years

Typically, you'd read it before calling the work function in the separate thread...
Yustme over 13 years

But i have to constantly read it. not just before it. the worker thread is an endless thread, which only stops when the program closes. this app works fine in WinForm, im migrating it to WPF
Reed Copsey over 13 years

@Yustme: Technically, it could be a problem in Windows Forms, as well... What version of C#/VS are you using?
Yustme over 13 years

okay thanks. think i need to do an extreme make over in the code. still not working.
Reed Copsey over 13 years

@Yustme: Better to just have the UI set the string, and poll on a string in a field/property. That way, you're not touching the control directly from your background thread...
Boern over 9 years

blog.somecreativity.com/2008/01/10/… might be of help as well