Question

I’m trying to change the text on my Form1’s textbox to “hello there” from within a thread.
But when I execute it, I get the error “Object reference not set to an instance of an object.”
When I check I see that txtboxCheckedFiels has a Null value.

How would I create an Object of that txtbox? (I have multiple threads running of which all should be able to change that text.

Code I’ve tried:

txtboxCheckedFiles.Invoke(new Action(() =>
                {
                    txtboxCheckedFiles.Text = "Hello there";
                }));

And another way i tried

var t = new Thread(
o => 
{
     txtboxCheckedFiles.BeginInvoke(
         ((Action)(() => txtboxCheckedFiles.Text = "Hello there")));
});

Answer 1

First you MUST check if invokation is required, and then you may invoke it.
Also, consider checking that there is a handle to the window, which means that windows is up and running (eg. this will fail if you try to load data in the constructor of the form)

if (this.InvokeRequired)
{
    IAsyncResult result = BeginInvoke(new MethodInvoker(delegate()
    {
        // DOSTUFF
    }));

    // wait until invocation is completed
    EndInvoke(result);
}
else if (this.IsHandleCreated)
{
    // DO STUFF
}