Writing to a TextBox from another thread

Question

I cannot figure out how to make a C  Windows Form application write to a textbox from a thread   For example in the Program cs we have the standard main   that draws the form   static void Main         Application EnableVisualStyles        Application SetCompatibleTextRenderingDefault false       Application Run new Form1         Then we have in the Form1 cs   public Form1         InitializeComponent         new Thread SampleFunction  Start       public static void SampleFunction         while true          WindowsFormsApplication1 Form1 ActiveForm Text     hi         Am I going about this completely wrong   UPDATE  Here is the working code sample provided from bendewey   public partial class Form1   Form       public Form1                 InitializeComponent            new Thread SampleFunction  Start               public void AppendTextBox string value                if  InvokeRequired                        this Invoke new Action lt string gt  AppendTextBox   new object    value                return                    textBox1 Text    value             void SampleFunction                    Gets executed on a seperate thread and             doesn t block the UI while sleeping         for int i   0  i lt 5  i                          AppendTextBox  hi                   Thread Sleep 1000

User · Accepted Answer

On your MainForm make a function to set the textbox the checks the InvokeRequired

public void AppendTextBox(string value)
{
    if (InvokeRequired)
    {
        this.Invoke(new Action<string>(AppendTextBox), new object[] {value});
        return;
    }
    ActiveForm.Text += value;
}

although in your static method you can't just call.

WindowsFormsApplication1.Form1.AppendTextBox("hi. ");

you have to have a static reference to the Form1 somewhere, but this isn't really recommended or necessary, can you just make your SampleFunction not static if so then you can just call

AppendTextBox("hi. ");

It will append on a differnt thread and get marshalled to the UI using the Invoke call if required.

Full Sample

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        new Thread(SampleFunction).Start();
    }

    public void AppendTextBox(string value)
    {
        if (InvokeRequired)
        {
            this.Invoke(new Action<string>(AppendTextBox), new object[] {value});
            return;
        }
        textBox1.Text += value;
    }

    void SampleFunction()
    {
        // Gets executed on a seperate thread and 
        // doesn't block the UI while sleeping
        for(int i = 0; i<5; i++)
        {
            AppendTextBox("hi.  ");
            Thread.Sleep(1000);
        }
    }
}

User · Answer

Have a look at Control BeginInvoke method  The point is to never update UI controls from another thread  BeginInvoke will dispatch the call to the UI thread of the control  in your case  the Form    To grab the form  remove the static modifier from the sample function and use this BeginInvoke   as shown in the examples from MSDN

User · Answer

or you can do like   public partial class Form1   Form       public Form1                 InitializeComponent            new Thread  SampleFunction   Start               void SampleFunction                    Gets executed on a seperate thread and             doesn t block the UI while sleeping         for   int i   0  i  lt  5  i                           this Invoke    MethodInvoker  delegate                                 textBox1 Text     hi                                Thread Sleep  1000

User · Answer

Most simple  without caring about delegates  if textBox1 InvokeRequired    true      textBox1 Invoke  MethodInvoker delegate   textBox1 Text    Invoke was needed       else     textBox1 Text    Invoke was NOT needed

User · Answer

You need to perform the action from the thread that owns the control   That s how I m doing that without adding too much code noise   control Invoke      gt  textBox1 Text     hi      Where Invoke overload is a simple extension from Lokad Shared Libraries        lt summary gt      Invokes the specified  lt paramref name  action   gt  on the thread that owns          the  lt paramref name  control   gt   lt  summary gt       lt typeparam name  TControl  gt type of the control to work with lt  typeparam gt       lt param name  control  gt The control to execute action against  lt  param gt       lt param name  action  gt The action to on the thread of the control  lt  param gt  public static void Invoke lt TControl gt  this TControl control  Action action     where TControl   Control     if   control InvokeRequired          action          else         control Invoke action

User · Answer

Here is the what I have done to avoid CrossThreadException and writing to the textbox from another thread   Here is my Button Click function- I want to generate a random number of threads and then get their IDs by calling the getID   method and the TextBox value while being in that worker thread    private void btnAppend Click object sender  EventArgs e         Random n   new Random         for  int i   0  i  lt  n Next 1 5   i                  label2 Text    UI Id      Thread CurrentThread ManagedThreadId  ToString             Thread t   new Thread getId           t Start              Here is getId  workerThread  code   public void getId         int id   Thread CurrentThread ManagedThreadId        Note that  I have collected threadId just before calling this Invoke       method else it would be same as of UI thread inside the below code block      this Invoke  MethodInvoker delegate                  inpTxt Text     My id is    --  id Environment NewLine

User · Answer

What s even easier is to just use the BackgroundWorker control

User · Answer

I would use BeginInvoke instead of Invoke as often as possible  unless you are really required to wait until your control has been updated  which in your example is not the case   BeginInvoke posts the delegate on the WinForms message queue and lets the calling code proceed immediately  in your case the for-loop in the SampleFunction   Invoke not only posts the delegate  but also waits until it has been completed    So in the method AppendTextBox from your example you would replace Invoke with BeginInvoke like that   public void AppendTextBox string value        if  InvokeRequired                this BeginInvoke new Action lt string gt  AppendTextBox   new object    value            return            textBox1 Text    value      Well and if you want to get even more fancy  there is also the SynchronizationContext class  which lets you basically do the same as Control Invoke Control BeginInvoke  but with the advantage of not needing a WinForms control reference to be known  Here is a small tutorial on SynchronizationContext

[c#] Writing to a TextBox from another thread?

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