创建新线程时，不会对GUI进行更改（C＃）

Question

With some help I have managed to create a new thread, although the method appears to execute, the conditions of the method either make a green or red light appear, although when running the method (Check1..etc) without the new thread the changes are reflected on the GUI (eg Red / Green Light Appears), but when creating a new thread and running the method the changes are not reflected on the Form / GUI.

// Method / Action to start the checks         private void StartChecks_Click(object sender, EventArgs e)
        {

            Thread t = new Thread(
               o =>
               {
                   InitChecks();
               });
            t.Start();
        }

// Check1 public void Check1()
        {

            // lets grabs the info from the config!
            var lines = File.ReadAllLines("probe_settings.ini");
            var dictionary = lines.Zip(lines.Skip(1), (a, b) => new { Key = a, Value = b })
                                  .Where(l => l.Key.StartsWith("#"))
                                  .ToDictionary(l => l.Key, l => l.Value);

            // lets set the appropriate value for this check field
            label1.Text = dictionary["#CheckName1"];

            // lets define variables and convert the string in the dictionary to int for the sock.connection method!

            int portno1;
            int.TryParse(dictionary["#PortNo1"], out portno1);

            // Convert hostname to IP, performance issue when using an invalid port on a hostname using the TcpClient class! 
            IPAddress[] addresslist = Dns.GetHostAddresses(hostname2);

            foreach (IPAddress theaddress in addresslist)
            {
                // Attempt to create socket and connect to specified port on host
                TcpClient tcP = new System.Net.Sockets.TcpClient();
                try
                {
                    tcP.ReceiveTimeout = 1;
                    tcP.SendTimeout = 1;
                    tcP.Connect(theaddress, portno1);
                    displayGreen1();
                    tcP.Close();
                }
                catch
                {
                    displayRed1();
                }
            }

        }

// Change the lights when the condition is met

        public void displayGreen1()
        {
            pictureBox2.Visible = false;
            pictureBox1.Visible = true;
        }

        private void displayRed1()
        {
            pictureBox2.Visible = true;
            pictureBox1.Visible = false;
        }

Answer 1

This is how WinForms is designed. You can't make changes from another thread. the solution usually is to use asynchronous delegate.

First of all add this declaration

 public delegate void MyDelegate1 ();

 public delegate void MyDelegate2 (); 

Then When you are in another thread You should do:

MyDelegate1 d1= new MyDelegate1 (displayGreen1);

 this.BeginInvoke(d1);

 MyDelegate2 d2= new MyDelegate2 (displayRed1);

 this.BeginInvoke(d2);

Answer 2

At your skill level, it would be best to:

• use timer in the form to check some status variable (say bool _pb1Visible and bool _pb2Visible )
• in the timer event update picturebox visibility
• in the thread, update ONLY bool member variables mentioned above.

It will work like a charm!

Simple example:

In your Check1() method, instead of:

displayGreen1();

put

_pb1Visible=true;
_pb1Visible=false;

and instead of

displayRed1();

put

_pb1Visible=false;
_pb1Visible=true;

Put the timer on the form. In the timer event, do the:

pictureBox2.Visible = _pb2Visible;
pictureBox1.Visible = _pb1Visible;

Answer 3

This is happening because UI controls can only be updated from the UI thread. When you do not create a new thread, the code which updates the controls runs on the UI thread, so it works as you expect. When you do create a new thread, because this thread is not the UI thread, the code which is supposed to update the controls fails to do so.

You can ensure that the code which updates the controls runs on the UI thread by changing the method calls to:-

this.BeginInvoke(new Action(() => displayRed1()));

and

this.BeginInvoke(new Action(() => displayGreen1()));

---

Incidentally (unrelated to your current problem):-

Try to avoid creating an explicit thread. Instead use the thread pool to manage the thread for you, eg ThreadPool.QueueUserWorkItem(x => InitChecks()) . (Note that this will still run on a non-UI thread so you still need to use BeginInvoke() as detailed above.). The thread pool knows best about when to create and execute a thread and using it will, ultimately, make your code more efficient.

Try to avoid catching all exception types in your try{...}catch{...} . This is stating that your code knows what to do when any type of exception is thrown. Instead, only catch exceptions which you know exactly how to handle,

eg

try
{
    ...
}
catch(TcpException)
{
    ...
}
catch(AnotherKnownException)
{
    ...
}
...

Note that it is OK to also have a catch block for all exception types as long as you rethrow the exception when exiting the block,

eg

try
{
    ...
}
catch(KnownException)
{
    ...
}
catch(Exception)
{
    // perform some logging, rollback, etc.
    throw;
}