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<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);         }     } } 

Answer 1

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);         }     } }