Multithreading in C#

[farnooshr65]

hi i'm new to multithreading in c#, i have this code:

namespace WindowsApplication4
{
    public partial class Form1 : Form
    {
         Thread t1;
         delegate void d1();
 
        public Form1()
        {
            InitializeComponent();
            t1 = new Thread(new ThreadStart(Sta));
            t1.IsBackground = false;
            t1.start();
        }
 
        public void Sta()
        {  
            button1.Invoke(new d1(DD));
        }
 
       public void DD()
        {
            webbrowser1 .Navigate("www.google.com");        
        }
     }          
  }
 
}

and it work.now i want to make it work with 2 threads,i want to have two threads,each one open a webbrowser and navigate google.com.i've written this code but it say's invoke cannot be used on a control until the window handle has been created.i don t know what to do.please help me

namespace WindowsApplication4
{
    public partial class Form1 : Form
    {
         Thread t1;
         delegate void d1();
         Thread t2;
         delegate void d2();
 
 
        public Form1()
        {
            InitializeComponent();
            t1 = new Thread(new ThreadStart(Sta));
            t1.IsBackground = false;
            t1.Start();
            t2 = new Thread(new ThreadStart(St));
            t2.IsBackground = false;
            t2.Start();
        }
 
 
        public void Sta()
        {          
            button1.Invoke(new d1(DD));
           // Use any form control for this ....
        }
 
 
        public void St()
        {
 
            button2.Invoke(new d2(DD2));
           // Use any form control for this ....
        }
 
 
       public void DD()
        {
            webbrowser1 .Navigate("www.google.com");       
         }
 
        public void DD2()
        {
           webBrowser2.Navigate("www.google.com");
        }
 
    }
 
}

[tlhintoq]

invoke cannot be used on a control until the window handle has been created

Where does it say this? Which line? Which control?
wbbbrowser1 and 2 are created outside of the code shown here. Is it possible you didn't initialize webbrowser2 the same as you did #1?

[farnooshr65]

no i created both browsers on my form.and the error is shown on button1.Invoke(new d1(DD)); lin 25 of secon code,but it doesn't show this same error on the first code

[Christian Binder]

The Invoke()-Method requires an already created Window-Handle.
You could put

object o = Handle;

between lines 13 and 14 respectively before you start the threads.
Referring to Handle causes the form to create a Window-Handle if it hasn't been created yet.

Also it would be possible to put the (thread-)code in an eventhandler of the HandleCreated-event. Within a handler of the Shown-event it should work as well.

The answer to your question, why the problem only occurs in the second code is (or could be ...) that in the first code the Window-Handle is created before the thread calls the Invoke-Method. In the second code you create a second thread after calling the first thread's Start()-method. Thread-creation is expensive, your main-thread (GUI-thread) is blocked when creating the 2nd thread but the first (already started) thread could call Invoke() meanwhile.