Why does inheriting a WPF Button change the appearance of the image in a toolbar.

Question

Using the following code btn2 looks different to btn1 and btn3 yet they are using exactly the same image.

Public Class MyToolBar
    Inherits ToolBar

    Public Sub New()
        MyBase.New()

        Dim bmp1 = New BitmapImage(ImageUri.DeleteItem)
        Dim bmp2 = New BitmapImage(ImageUri.DeleteItem)
        Dim bmp3 = New BitmapImage(ImageUri.DeleteItem)
        Dim img1 = New Image With {.Source = bmp1}
        Dim img2 = New Image With {.Source = bmp2}
        Dim img3 = New Image With {.Source = bmp3}

        Dim btn1 = New Button With {.Content = img1}
        Dim btn2 = New MyButton With {.Content = img2}
        Dim btn3 = New Button With {.Content = img3}

        Me.AddChild(btn1)
        Me.AddChild(btn2)
        Me.AddChild(btn3)

    End Sub

End Class

Public Class MyButton
    Inherits Button
End Class

The only difference in the code is btn2 is constructed with MyButton. MyButton is a simple inheritance of Button, no other code.

btn1 & btn3 appear as expected; flat. btn2 appears semi raised and has a black border.

The order I add the buttons to the toolbar makes no difference. That is - the weird appearance of btn2 moves to the location that it is added to the toolbar.

I've dumped and compared the properties, to 2 levels, of btn1 and btn2 and there is only the expected differences except for:

btn1.DependencyObjectType.IsSecurityCritical=False btn2.DependencyObjectType.IsSecurityCritical=True

and

btn1.DependencyObjectType.IsSecurityTransparent=True btn2.DependencyObjectType.IsSecurityTransparent=False

Anything else I should look into?

Answer 1

Check you XAML for a default style that applies to MyButton.

Update: The standard WPF themes include default styles for well-known controls. Your MyButton is not one of those. You need to extend the theme dictionary with style for your class, or you need to declare a default style for your class that is based on the Button style.

Here's the simplest style you can try adding to your resource dictionary (where local: is the XAML declaration of your CLR namespace - you need to add this to your root XAML element)

<Style BasedOn="{StaticResource {x:Type Button}}"
       TargetType="{x:Type local:MyButton}" />

Update 2: If your button is part of a toolbar, try this one instead (:-P):

<Style BasedOn="{StaticResource {x:Static ToolBar.ButtonStyleKey}}"
       TargetType="{x:Type local:MyButton}" />