Have a problem

In use C# When writing a form application , When debugging, an error is suddenly reported , Say my thread operation is invalid , Not from the thread that created the control to access the control .

The reason for this problem is ：

C# Only the main thread can access the control .

from .NET Framework 2.0 Class library start ,.net The framework is for winform In this paper, we use multithreading to call the form control for security detection , That is to say, if I call the form control from another thread that is not the main thread , There will be an exception .

resolvent

There are many ways to solve cross thread calls , Here are two .

1. Turn off the security check of cross thread access control directly

Turn off security checks , We just need to add the following code to the form function ：

public Form1()
{
    
    InitializeComponent();
    Control.CheckForIllegalCrossThreadCalls = false;	//  This code turns off the security check 
}

This method is the simplest , It directly turns off the security check of cross thread access control , Then you can allow you to randomly change the properties of the control in other sub threads , Such access is uncontrollable , So this method is not recommended .

2. Call... Through a delegate

C# Delegate call of , similar C The function pointer in the language is the same as the function parameter .

C# Provides delegate and invoke To call the control from other threads .

The simplified method of use is as follows , It is directly in the part of code that needs cross thread access to controls , Written in delegate Just enclose the inside .

this.Invoke(new EventHandler (delegate 
{
    //  This is the code related to the access control 
	label1.Text = "hello"; 
}));

such as , I met it at the beginning , I am in a thread of network data receiving , Write the received data into the received text box , No addition Invoke That would be wrong , If you add it, you won't , The following code ：

private void ReceiveCallback(IAsyncResult AR)
{
    
    // Check how much bytes are recieved and call EndRecieve to finalize handshake
    this.Invoke(new EventHandler(delegate
    {
    
        try
        {
    
            int recieved = tcpClient.EndReceive(AR);

            if (recieved <= 0)
                return;

            string message = Encoding.GetEncoding("GBK").GetString(recieveBuffer, 0, recieved);     //  Only convert the received data 
			
            //  Here is cross thread access tbRecv Text box control , This is actually to add the received data to the text box to display 
            tbRecv.AppendText($"[{
      DateTime.Now.ToString("yyy-MM-dd HH.mm.ss.fff")}] {
      message}\r\n");

            // Start receiving again
            tcpClient.BeginReceive(recieveBuffer, 0, recieveBuffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), null);
        }
        catch (SocketException ex)
        {
    
            MessageBox.Show(ex.ToString());
        }
   }));
}