Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on

Solution 1:

As per Prerak K's update comment (since deleted):

I guess I have not presented the question properly.

Situation is this: I want to load data into a global variable based on the value of a control. I don't want to change the value of a control from the child thread. I'm not going to do it ever from a child thread.

So only accessing the value so that corresponding data can be fetched from the database.

The solution you want then should look like:

UserContrl1_LOadDataMethod()
{
    string name = "";
    if(textbox1.InvokeRequired)
    {
        textbox1.Invoke(new MethodInvoker(delegate { name = textbox1.text; }));
    }
    if(name == "MyName")
    {
        // do whatever
    }
}

Do your serious processing in the separate thread before you attempt to switch back to the control's thread. For example:

UserContrl1_LOadDataMethod()
{
    if(textbox1.text=="MyName") //<<======Now it wont give exception**
    {
        //Load data correspondin to "MyName"
        //Populate a globale variable List<string> which will be
        //bound to grid at some later stage
        if(InvokeRequired)
        {
            // after we've done all the processing, 
            this.Invoke(new MethodInvoker(delegate {
                // load the control with the appropriate data
            }));
            return;
        }
    }
}

Solution 2:

Threading Model in UI

Please read the Threading Model in UI applications (old VB link is here) in order to understand basic concepts. The link navigates to page that describes the WPF threading model. However, Windows Forms utilizes the same idea.

The UI Thread

• There is only one thread (UI thread), that is allowed to access System.Windows.Forms.Control and its subclasses members.
• Attempt to access member of System.Windows.Forms.Control from different thread than UI thread will cause cross-thread exception.
• Since there is only one thread, all UI operations are queued as work items into that thread:

• If there is no work for UI thread, then there are idle gaps that can be used by a not-UI related computing.
• In order to use mentioned gaps use System.Windows.Forms.Control.Invoke or System.Windows.Forms.Control.BeginInvoke methods:

BeginInvoke and Invoke methods

• The computing overhead of method being invoked should be small as well as computing overhead of event handler methods because the UI thread is used there - the same that is responsible for handling user input. Regardless if this is System.Windows.Forms.Control.Invoke or System.Windows.Forms.Control.BeginInvoke.
• To perform computing expensive operation always use separate thread. Since .NET 2.0 BackgroundWorker is dedicated to performing computing expensive operations in Windows Forms. However in new solutions you should use the async-await pattern as described here.
• Use System.Windows.Forms.Control.Invoke or System.Windows.Forms.Control.BeginInvoke methods only to update a user interface. If you use them for heavy computations, your application will block:

Invoke

• System.Windows.Forms.Control.Invoke causes separate thread to wait till invoked method is completed:

BeginInvoke

• System.Windows.Forms.Control.BeginInvoke doesn't cause the separate thread to wait till invoked method is completed:

Code solution

Read answers on question How to update the GUI from another thread in C#?. For C# 5.0 and .NET 4.5 the recommended solution is here.