getting error - System.InvalidOperationException was unhandled

c#, invalidoperationexception, multithreading

Solution

`You can access Form GUI controls in GUI thread` and you are trying to access outside GUI thread that is the reason for getting exception. You can use MethodInvoker to access controls in the GUI thread.

void sendMethod()
{
    MethodInvoker mi = delegate{
       string lblText = (String) MsgSender.sendSMS(to, msg, "hotmail", uname, pwd);
       pictureBox1.Visible = false;
       lblMsgStatus.Visible = true;
       lblMsgStatus.Text = 
             lblText + "\nFrom: " + uname + 
             " To: " + cmbxNumber.SelectedItem + " " + count;
   }; 

   if(InvokeRequired)
       this.Invoke(mi);
}

Problem

I have just started to learn windows application development, and we have been given self learn project to develop one windows application. I am trying to create the application to send email. I have created a class `MsgSender.cs` to handle that. When I call that class from main form I am getting the following error System.InvalidOperationException was unhandled. Error Message--> Cross-thread operation not valid: Control 'pictureBox1' accessed from a thread other than the thread it was created on.` The stacktrace is as follows: ``` System.InvalidOperationException was unhandled Message=Cross-thread operation not valid: Control 'pictureBox1' accessed from a thread other than the thread it was created on. Source=System.Windows.Forms StackTrace: at System.Windows.Forms.Control.get_Handle() at System.Windows.Forms.Control.SetVisibleCore(Boolean value) at System.Windows.Forms.Control.set_Visible(Boolean value) at UltooApp.Form1.sendMethod() in D:\Ultoo Application\UltooApp\UltooApp\Form1.cs:line 32 at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() InnerException: ``` Code: ``` private void btnSend_Click(object sender, EventArgs e) { pictureBox1.Visible = true; count++; lblMsgStatus.Visible = false; getMsgDetails(); msg = txtMsg.Text; Thread t = new Thread(new ThreadStart(sendMethod)); t.IsBackground = true; t.Start(); } void sendMethod() { string lblText = (String)MsgSender.sendSMS(to, msg, "hotmail", uname, pwd); pictureBox1.Visible = false; lblMsgStatus.Visible = true; lblMsgStatus.Text = lblText + "\nFrom: " + uname + " To: " + cmbxNumber.SelectedItem + " " + count; } ```

Original source