How can you resize a User Control at design time using code? [modified]

Paul Hasler

The Situation I have created a user control which is similar to a standard slider control but which has quite at few different features such as multiple slider pointers. The control uses an image to visualise the slider strip background.

Private mySliderStripImage As Image = My.Resources.Horizontal\_Slider\_\_\_Basic\_V1\_\_\_Strip

To make the user control more flexible at design time, I've included a SliderStripImage property.

<Description("(As Image) The image to use for the Slider Strip.")> \_
Property SliderStripImage() As Image
    Get
        SliderStripImage = mySliderStripImage
    End Get
    Set(ByVal value As Image)
        mySliderStripImage = value
    End Set
End Property

The control functions correctly, and when I'm working with the control at design time I can change the SliderStripImage property. The Problem If I change the SliderStripImage property to an image of a different size at design time, I have to manually resize the control to suit. That is, if I change to a larger image, I have to manually increase the size of the control in order to be able to see all of the new larger image. I can get the dimensions of the new image with SliderStripImage.Width and SliderStripImage.Height, but how can I get the size of the control to update itself with these values at design time?:confused: I thought I'd be able to do it with something along the lines of

Me.Size.Width = SliderStripImage.Width
Me.Size.Height = SliderStripImage.Height

But this doesn't work. I get the message "Expression is a value and therefore cannot be the target of an assignment." Any advice greatly appreciated. Paul

modified on Monday, February 16, 2009 4:38 AM

Paul Hasler · modified on Monday, February 16, 2009 4:38 AM

Well after a few more hours of banging my head against the keyboard I've managed to get a solution that works. But to be honest I don't fully understand why it works. Perhaps someone with a bit more knowledge could explain it? While reading more about the System.Windows.Forms.UserControl class in the MSDN (http://msdn.microsoft.com/en-us/library/system.windows.forms.usercontrol.aspx[^]), I noticed the following lines in some example code:

     ' Size the user control.
     Size = New System.Drawing.Size(375, 150)

So I modified my SliderStripImage property to

<Description("(As Image) The image to use for the Slider Strip.")> \_
Property SliderStripImage() As Image
    Get
        SliderStripImage = mySliderStripImage
    End Get
    Set(ByVal value As Image)
        mySliderStripImage = value
        Size = New System.Drawing.Size(SliderStripImage.Width, SliderStripImage.Height)
    End Set
End Property

This raises some questions: 1.Why haven't we had to specify what Size refers to with something like Me.Size? 2.Why are we creating a New object every time the property changes? Doesn't the control already exist? Of course, nobody likes putting lines of code in their work that they don't understand themselves. :sigh: Can anyone shed some light on this?:confused: Regards Paul

riced

1. In the MSDN example:

Public Class MyCustomerInfoUserControl
Inherits System.Windows.Forms.UserControl

MyCustomerInfoUserControl has a property Size inherited from UserControl hence any reference to Size in a method of of the MyCustomerInfoUserControl class does not need to be qualified. It refers to the property of the current instance. 2. The Size property is of type System.Drawing.Size. The new is creating a new instance of a System.Drawing.Size object not a new MyCustomerInfoUserControl control.

Regards David R

Paul Hasler

Ah ha! Thanks for the lightbulb moment David! :-D 1. This works in my code because my slider user control would also inherit from System.Windows.Forms.UserControl right? I'm using Visual Studio 2008 Express, and when I added a User Control, the template would have set up the inheritance in the hidden code. I didn't see it in the visible code which helped my confusion. 2. I think I get it. We're creating a new System.Drawing.Size object with the dimensions we want, and then setting the Size property of our existing System.Windows.Forms.UserControl to have the same Width and Height values as this new object.

riced

As Julie Andrews sang "By George he's got it!" That's what I think is happening.

Regards David R