C# Multi threading- Move objects between threads

Question

i am working with a winforms control that is both a GUI element and also does some internal processing that has not been exposed to the developer. When this component is instantiated it may take between 5 and 15 seconds to become ready so what i want to do is put it on another thread and when its done bring it back to the gui thread and place it on my form. The problem is that this will (and has) cause a cross thread exception.

Normally when i work with worker threads its just with simple data objects i can push back when processing is complete and then use with controls already on the main thread but ive never needed to move an entire control in this fashion.

Does anyone know if this is possible and if so how? If not how does one deal with a problem like this where there is the potential to lock the main gui?

Answer 1

You don't need to lock the GUI, you just need to call invoke:

Controls in Windows Forms are bound to a specific thread and are not thread safe. Therefore, if you are calling a control's method from a different thread, you must use one of the control's invoke methods to marshal the call to the proper thread. This property can be used to determine if you must call an invoke method, which can be useful if you do not know what thread owns a control. ref

Here is how it looks in code:

public delegate void ComponentReadyDelegate(YourComponent component);
public void LoadComponent(YourComponent component)
{
    if (this.InvokeRequired)
    {
        ComponentReadyDelegate e = new ComponentReadyDelegate(LoadComponent);
        this.BeginInvoke(e, new object[]{component});
    }
    else
    {
        // The component is used by a UI control
        component.DoSomething();
        component.GetSomething();
    }
}

// From the other thread just initialize the component
// and call the LoadComponent method on the GUI.
component.Initialize(); // 5-15 seconds
yourForm.LoadComponent(component);

Normally calling the LoadComponent from another thread will cause a cross-thread exception, but with the above implementation the method will be invoked on the GUI thread.

InvokeRequired tells you if:

the caller must call an invoke method when making method calls to the control because the caller is on a different thread than the one the control was created on. ref

Update:
So if I understand you correctly the control object is created on a thread other than the GUI thread, therefore even if you were able to pass it to the GUI thread you still won't be able to use it without causing a cross-thread exception. The solution would be to create the object on the GUI thread, but initialize it on a separate thread:

public partial class MyForm : Form
{
    public delegate void ComponentReadyDelegate(YourComponent component);
    private YourComponent  _component;
    public MyForm()
    {
        InitializeComponent();
        // The componet is created on the same thread as the GUI
        _component = new YourComponent();

        ThreadPool.QueueUserWorkItem(o =>
        {
            // The initialization takes 5-10 seconds
            // so just initialize the component in separate thread
            _component.Initialize();

            LoadComponent(_component);
        });
    }

    public void LoadComponent(YourComponent component)
    {
        if (this.InvokeRequired)
        {
            ComponentReadyDelegate e = new ComponentReadyDelegate(LoadComponent);
            this.BeginInvoke(e, new object[]{component});
        }
        else
        {
            // The component is used by a UI control
            component.DoSomething();
            component.GetSomething();
        }
    }
}