将在另一个线程中创建的UserControl添加到窗体

Question

I have an application that has a form named as MainAppForm (Thread1). I have a panel in this form which will host UserControls.

When a user clicks the button, I want to create another thread (Thread2) which will create an instance of the UserControl and call a method that is on the Thread1 to add UserControl to the panel in mentioned in the first paragraph.

This is how I call main Thread1 from Thread2

public class SecondThread
{
    public void start()
    {
        ModuleWindow userControl = new ModuleWindow(new Module.ModuleLayer());

        Global.SetModuleWindowThreadSafe(userControl);
    }
}

My method that will add the passed in user control to the panel.

public static class Global
{
    private delegate void SetModuleWindowThreadSafeDelegate(UserControl userControl);
    public static void SetModuleWindowThreadSafe(UserControl userControl)
    {
        if (Global.mainAppForm.pnlMain.InvokeRequired)
        {
            Global.mainAppForm.pnlMain.Invoke(
                new SetModuleWindowThreadSafeDelegate(SetModuleWindowThreadSafe),
                userControl);
        }
        else
        {
            Global.mainAppForm.pnlMain.Controls.Add(userControl);
        }
    }
}

After I do the call in the SetModuleWindowThreadSafe() method it raises

Cross-thread operation not valid: Control 'menuStrip1' accessed from a thread other than the thread it was created on.

Note: menuStrip1 is a control on UserControl.

How can I add the UserControl that is created in the second thread to the panel???

UPDATED:

Thanks for the answers. I am sure they're helpful in some ways but not in my condition. The reason is my MainAppForm(AKTAP project) and the generated UserControl's(KKM project) are being created in different projets even solutions. The project output of KKM is a .dll and I am loading those dll files on runtime using reflections. So MainAppForm does not know what type of usercontrols and controls are being generated in each dll.

What I want to do is in the following order:

1- AKTAP project has an interface which is implemented by a class in KKM project.
2- KKM project is being built and puts dll files to a specified directory.
3- AKTAP starts to run and loads dll files using reflections by filtering the interface mentioned in 1.
4- AKTAP calls a method in KKM hich will generate and return the usercontrol.
5- AKTAP adds the returned usercontrol to the MainAppForm. (And this is where I get the exception above.)

Answer 1

How can I add the UserControl that is created in the second thread to the panel?

You don't. You create the UserControl in the UI thread, rather than in some background thread.

If you have some expensive CPU bound computation to do in order to figure out what data the user control will need then use another thread to compute that data and then have the UI thread take that data and create the UI controls to display it.

Answer 2

Servy is correct - you don't.

However, you can! Meaning, it is possible.

Passing data from a thread is complicated, but the System.ComponentModel.BackgroundWorker (part of WinForms) greatly simplifies threading operations and makes tasks like this rather fun to do.

Here is a generic technique that uses two (2) Windows Forms, one as a variable inside the other. Both are in the same namespace (same project, etc).

Form1:

public partial class Form1 : Form
{

    private Button btnGetInteger;
    private Button btnGetMenuStrip;
    private Button btnGetString;
    private Form2 _form2;
    private Form2.ReturnType _getType;
    private Object _form2Argument;

    public Form1()
    {
        InitializeComponent();
        btnGetInteger = new Button();
        btnGetInteger.Click += Form2_GetInteger;
        btnGetMenuStrip = new Button();
        btnGetMenuStrip.Click += Form2_GetInteger;
        btnGetString = new Button();
        btnGetString.Click += Form2_GetString;
        Shown += (s, e) => { Form2_CreateMenuStrip(s, EventArgs.Empty); };
    }

    public void Form2_ThreadChanged(object sender, ProgressChangedEventArgs e)
    {
        var returned = (Form2.ReturnType)e.ProgressPercentage;
        switch (returned)
        {
            case Form2.ReturnType.MenuStrip:
                var menuStrip = (MenuStrip)e.UserState;
                this.Controls.Add(menuStrip);
                break;
            case Form2.ReturnType.Integer:
                var numberBack = (int)e.UserState;
                Text = String.Format("Form1 : (int){0}", numberBack);
                break;
            case Form2.ReturnType.String:
                var stringBack = e.UserState.ToString();
                Text = String.Format("Form1 : (String){0}", stringBack);
                break;
        }
    }

    public void Form2_ThreadCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        _form2Argument = null;
        if (e.Error != null)
        {
            String title;
            if (_form2 != null)
            {
                title = String.Format("{0}: {1}", _form2.Text, e.Error.GetType());
            } else
            {
                title = String.Format("Form2: {0}", e.Error.GetType());
            }
            MessageBox.Show(e.Error.Message, title, MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
        if (_form2 != null)
        {
            _form2.Close();
            _form2.Dispose();
            _form2 = null;
        }
        btnGetInteger.Enabled = true;
        btnGetMenuStrip.Enabled = true;
        btnGetString.Enabled = true;
    }

    private void Form2_CreateMenuStrip(object sender, EventArgs e)
    {
        if (_form2 == null)
        {
            _getType = Form2.ReturnType.MenuStrip;
            var item = new ToolStripMenuItem(Text);
            item.Click += Form2_GetInteger;
            _form2Argument = item;
            Form2_StartWork();
        }
    }

    private void Form2_GetInteger(object sender, EventArgs e)
    {
        if (_form2 == null)
        {
            _getType = Form2.ReturnType.Integer;
            Form2_StartWork();
        }
    }

    private void Form2_GetString(object sender, EventArgs e)
    {
        if (_form2 == null)
        {
            _getType = Form2.ReturnType.String;
            Form2_StartWork();
        }
    }

    private void Form2_StartWork()
    {
        btnGetInteger.Enabled = false;
        btnGetMenuStrip.Enabled = false;
        btnGetString.Enabled = false;
        _form2 = new Form2();
        _form2.Show(); // Show returns immediately
        _form2.StartThread(this, _form2Argument, _getType);

    }

}

Form2_ThreadChanged and Form2_ThreadCompleted are both set to PUBLIC so that they can be visible by the instance of Form2 .

Form2:

public partial class Form2 : Form
{
    private ReturnType _getType; // thread safe
    private BackgroundWorker _bwThread;

    public enum ReturnType { MenuStrip, String, Integer }

    public Form2() // Do Not Call this method
    {
        InitializeComponent();
    }

    public void StartThread(Form1 parent, Object argument, ReturnType getType)
    {
        _getType = getType;
        if (_bwThread == null)
        {
            _bwThread = new BackgroundWorker() {
                WorkerReportsProgress = true,
                WorkerSupportsCancellation = true
            };
            _bwThread.DoWork += ThreadWork;
            _bwThread.ProgressChanged += parent.Form2_ThreadChanged;
            _bwThread.RunWorkerCompleted += parent.Form2_ThreadCompleted;
        }
        if (!_bwThread.IsBusy)
        {
            _bwThread.RunWorkerAsync(argument);
        }
    }

    private void ThreadWork(object sender, DoWorkEventArgs e)
    {
        switch (_getType)
        {
            case ReturnType.MenuStrip:
                var menuStrip = new MenuStrip();
                if (e.Argument != null)
                {
                    var mi = (ToolStripMenuItem)e.Argument;
                    menuStrip.Items.Add(mi);
                }
                _bwThread.ReportProgress((int)_getType, menuStrip);
                break;
            case ReturnType.Integer:
                var numberBack = 1;
                _bwThread.ReportProgress((int)_getType, numberBack);
                break;
            case ReturnType.String:
                var stringBack = "Worker String";
                _bwThread.ReportProgress((int)_getType, stringBack);
                break;
        }
    }

}

If you make a new, small project with 2 empty forms in it called Form1 and Form2, you can go into the code and simply paste everything from above into those two forms.

With that done, just put breakpoints on all of the methods (both public and private) to see how they work.