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Problem description:
The windows program on the client uses webmethod to obtain a list of system information from the server. There are multiple messages in the information list. When the system message time meets the requirements, use a custom messageform to show the system message. Messageform is a winform containing webbrowser. The show messageform call is executed in a timer. The following error occurs when you call the showmessage operation.
Error code:
Private void btntests_click (Object sender, eventargs E)
{
Datarow ROW = (New datatable (). newrow ();
System. Threading. Timer timer = new system. Threading. Timer (
New system. Threading. timercallback (showmessageforms ),
Row,
0,
30000 );
}
Private void showmessageforms (Object status)
{
(New messageform (). Show ();
} |
An error occurred when new messageform calls its initializecomponent () method. If you delete the webbrowser control on messageform, the program can show the form normally without errors. Problem investigation:
From the program error information, we can see that it may be an ActiveX suite problem. ActiveX webbrowser requires that the current thread is a single-thread apartment. The webbrowser COM component requires that the current thread be a single-suite, while the thread from system. Threading. Timer is a mtathread multi-suite. A problem occurs. Solution:
Solution 1: Use a new thread to start messageform and set the apartmentstate of this thread to sta
Private void btntestt_click (Object sender, eventargs E)
{
Datarow ROW = (New datatable (). newrow ();
System. Threading. Timer timer = new system. Threading. Timer (
New system. Threading. timercallback (showmessageformt ),
Row,
0,
300000 );
}Private void showmessageformt (Object status)
{
System. Threading. Thread thread = new system. Threading. Thread (
New system. Threading. parameterizedthreadstart (showmessage ));
Thread. setapartmentstate (system. Threading. apartmentstate. Sta );
Thread. Start (Status );
} Private void showmessage (Object status)
{
System. Windows. Forms. application. Run (New messageform ());
(New messageform (). showdialog ();
} |
Solution 2: Find the main UI thread and schedule it with the main UI thread. Show messageform
Private void btntestg_click (Object sender, eventargs E)
{
Datarow ROW = (New datatable (). newrow ();
System. Threading. Timer timer = new system. Threading. Timer (
New system. Threading. timercallback (showmessageformg ),
Row,
0,
300000 );
}
Private delegate void showmessagehandler (datarow row );
Private void showmessageformg (Object status)
{
If (system. Windows. Forms. application. openforms [0]. invokerequired)
{
System. Windows. Forms. application. openforms [0]. Invoke (New showmessagehandler (showmessageformg), new object [] {status });
Return;
}
Showmessage (Status );
}
Private void showmessage (Object status)
{
(New messageform (). showdialog ();
} |
In the example, datarow ROW = (New able (). newrow (); has no practical significance. In actual code, showmessage requires a datarow to draw messages. In the sample code, datarow is only used to simulate the actual environment and has no practical significance.
Add another method public partial class Form1 : Form
{
private void button1_Click(object sender, EventArgs e)
{
System.Threading.Thread s = new System.Threading.Thread(new System.Threading.ThreadStart(test));
s.ApartmentState = System.Threading.ApartmentState.STA;
s.Start();
}
public void test()
{
this.Invoke(new EventHandler(this.invokeTest));
}
public void invokeTest(object sender,EventArgs e)
{
System.Windows.Forms.WebBrowser wb = new WebBrowser();
this.Controls.Add(wb);
}
public Form1()
{
InitializeComponent();
}
} |
