Question

Learning C#, WPF. I’ve come across a problem I can’t solve by research alone.

I want to update the text of a textbox control from another thread which is present in another class.

I know the thread is started, working and has data I can use to populate the text box. What I can’t figure out is how to address the text box control in the GUI from the second thread.

My text box control is called ‘txt_CPU’ and I want ‘cpuCount’ to appear in it. I’m sure I need to use delegation, but I can’t relate the examples to my code.

Help is appreciated. (I’m sure there are may other ‘problems’ in my code, this is rough learning in progress)

So we have the thread creation.

 public MainWindow()
        {
            InitializeComponent();

            //start a new thread to obtain CPU usage
            PerformaceClass pc = new PerformaceClass();
            Thread pcThread = new Thread(pc.CPUThread); 
            pcThread.Start();

        }

The Class it’s calling

 public class PerformaceClass
    {

            public string getCPUUsage()
            {
                PerformanceCounter cpuCounter;

                cpuCounter = new PerformanceCounter();

                cpuCounter.CategoryName = "Processor";
                cpuCounter.CounterName = "% Processor Time";
                cpuCounter.InstanceName = "_Total";
                return cpuCounter.RawValue.ToString() + "%";

            }

        public void CPUThread()
        {
            PerformaceClass PC = new PerformaceClass();

            int i = 0;
            while (i < 5)
            {
                string cpuCount = PC.getCPUUsage();
                i++;
                System.Threading.Thread.Sleep(500);
                // MessageBox.Show(cpuCount);

            }   
        }
    }

Answer 1

One way is to add an event handler to your PerformaceClass like this:

 public class PerformanceClass
 {
     public event EventHandler<PerformanceEventArgs> DataUpdate;

     ....
     public void CPUThread()
     {
        int i = 0;
        while (i++ < 5)
        {
            string cpuCount = getCPUUsage();
            OnDataUpdate(cpuCount);
            System.Threading.Thread.Sleep(500);

        }   
     }

     private void OnDataUpdate(string data)
     { 
          var handler = DataUpdate;
          if (handler != null)
          {
               handler(this, new PerformanceEventArgs(data));
          }
     }
 }

 public class PerformanceEventArgs: EventArgs
 {
       public string Data { get; private set; }
       public PerformanceEventArgs(string data)
       {
            Data = data;
       }
 }

Then use it in your main like this:

public MainWindow()
{
    InitializeComponent();

    //start a new thread to obtain CPU usage
    PerformanceClass pc = new PerformanceClass();
    pc.DataUpdate += HandleDataUpdate;
    Thread pcThread = new Thread(pc.CPUThread); 
    pcThread.Start();
}

private void HandleDataUpdate(object sender, PerformanceEventArgs e)
{
     // dispatch the modification to the text box to the UI thread (main window dispatcher)
     Dispatcher.BeginInvoke(DispatcherPriority.Normal, () => { txt_CPU.Text = e.Data });
}

Note that I fixed the typo in the PerformanceClass (missing n).