R – HowTo write a recursive Custom Control in WinForms .NET

controlsrecursionuser-controlswinforms

I am attempting to write a 'User Control' in WinForms .NET (not ASP.NET). The control is relatively simple. It will contain a label, a button, and a DataGridView.

However, the control needs to be able to instantiate itself, i.e. when the user clicks the button (of the parent control) at least 1 nested (children) control of the same type will be displayed underneath (kind of like a Tree)

I am having no success writing such a recursive control using a 'User Control'. A StackOverflow Exception occurs when instantiating MyControl within it's own constructor.

Therefore, I am leaning towards using a 'Custom Control', hoping it can handle the instantiation of itself (maybe in the Paint event??). Alot more work has to go into a Custom Control however, so I don't want to go down this path if it's going to take forever. I am on a tight deadline.

Anybody done this using a Custom Control or have any solid ideas on how to create a recursive control?

By the way, this control would be used in a fairly finite number of recursive combinations, so maybe it would be better to create a separate control for each parent/children scenario? I am thinking that would result in at least 10 separate user controls.

thanks for your help

UPDATE (here is my initial attempt at a stop condition per your feedback, but this is still causing children to be created indefinitely) :


public partial class CustomX : UserControl
    {
        private IList _children = new List();

        public CustomX()
        {
            InitializeComponent();

            Recurse(0);

        }

        private void Recurse(int childCount)
        {
            if (childCount

Best Answer

The problem is probably that the child control also instantiates a child control. There has to be a stop condition or controls will be generated until the stack overflows.

This should work:

public partial class CustomX : UserControl
    {
        private IList _children = new List();

        public CustomX(int depth)
        {
            InitializeComponent();
            if(depth > 0)
            {
                CustomX child = new CustomX(depth-1);
                this.Controls.Add(child)
            }
        }
    }

Related Solutions

.net – Control vs UserControl in WinForms

Here is a good article about this question. user controls

However in short

A Control is either inherited or completely custom. You write and handle many of the events yourself. You can even control how and when the control is drawn thru the use of GDI+ drawing.

A UserControl is a collection of controls placed together to be used in a certain way. For example you can place a GroupBox that contains Textbox’s, Checkboxes, etc. This is useful when you have to place the same group of controls on/in multiple forms or tabs. Note: you can write some custom events and drawing for UserControls also.

Winforms – How to expose and raise custom events for a vb.net winforms user control

To use custom events for bubbling the events of another control, you can do like this:

Public Custom Event AddRemoveAttendees As EventHandler
    AddHandler(ByVal value As EventHandler)
        AddHandler _theButton.Click, value
    End AddHandler

    RemoveHandler(ByVal value As EventHandler)
        RemoveHandler _theButton.Click, value
    End RemoveHandler

    RaiseEvent(ByVal sender As Object, ByVal e As System.EventArgs)
        ' no need to do anything in here since you will actually '
        ' not raise this event; it only acts as a "placeholder" for the '
        ' buttons click event '
    End RaiseEvent
End Event

In AddHandler and RemoveHandler you simply propagate the call to attach or remove the given event handler to/from the control's Click event.

To expand a bit on the use of custom events, here is another sample implementation of a custom event:

Dim _handlers As New List(Of EventHandler)
Public Custom Event AddRemoveAttendees As EventHandler

    AddHandler(ByVal value As EventHandler)
        _handlers.Add(value)
    End AddHandler

    RemoveHandler(ByVal value As EventHandler)
        If _handlers.Contains(value) Then
            _handlers.Remove(value)
        End If
    End RemoveHandler

    RaiseEvent(ByVal sender As Object, ByVal e As System.EventArgs)
        For Each handler As EventHandler In _handlers
            Try
                handler.Invoke(sender, e)
            Catch ex As Exception
                Debug.WriteLine("Exception while invoking event handler: " & ex.ToString())
            End Try
        Next
    End RaiseEvent
End Event

Now, as it looks above, it does little else than a regular event declaration:

Public Event AddRemoveAttendees As EventHandler

It provides a similar mechanism allowing for event handlers to be attached and removed, and for the event to be raised. What the Custom event adds is an extra level of control; you get to write some code around the adding, removing and raising of the event, in which you can enforce rules, and tweak what will happen a little bit. For instance, you may want to limit the number of event handlers that are attached to your event. To achieve that you can alter the AddHandler section from the sample above:

    AddHandler(ByVal value As EventHandler)
        If _handlers.Count < 8 Then
            _handlers.Add(value)
        End If
    End AddHandler

If you don't need that kind of detailed control, I see no need to declare custom events.

Best Answer

Related Solutions

.net – Control vs UserControl in WinForms

Winforms – How to expose and raise custom events for a vb.net winforms user control

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