C++ – Update statusbar from a thread using C++/CLI

c++-climultithreadingwinforms

I'm sure this is a pretty straight forward question. I'm writing a small windows forms app using C++/CLI. When the form initializes, I start a thread that will process some code. When the code in the thread is executed, I want the thread to somehow update the text in a statusbar in the bottom of the window. So I was thinking something like this:

I create an event.
Then I create the Thread that will do some processing.
When the processing is done, fire an event that makes the text in the statusbar update.

Is this a reasonable way to go? If so, how do I update the statusbar from within the thread? Maybe there is a smarter way to acheive this?

Best Answer

Declare a method like that changes the status text given a string:

private: void UpdateStatus(String^ msg) {
    statusBar.Text = msg;
}

and from the other thread, use Invoke:

Invoke(gcnew Action<String^>(this, &Form1::UpdateStatus), "message");

Invoke will call the given delegate with the specified parameters on the UI thread.

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

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;
        }
    }
}

The difference between a process and a thread

Both processes and threads are independent sequences of execution. The typical difference is that threads (of the same process) run in a shared memory space, while processes run in separate memory spaces.

I'm not sure what "hardware" vs "software" threads you might be referring to. Threads are an operating environment feature, rather than a CPU feature (though the CPU typically has operations that make threads efficient).

Erlang uses the term "process" because it does not expose a shared-memory multiprogramming model. Calling them "threads" would imply that they have shared memory.

Best Answer

Related Solutions

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

The difference between a process and a thread

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