Wpf binding to a function
- by carlopenid
I've a created a simple scrollviewer (pnlDayScroller) and want to have a separate horizontal scrollbar (associated scroller) to do the horizontal scrolling. All works with the below code accept I need to bind the visibility of the associated scroller.
I can't simply bind this to the visibility property of the horizontal template part of the scroll viewer as I've set this to be always hidden. The only way I can think to do this is to bind the visibility of the associated scroller to a function such that
If associatedScroller.scrollableWidth > 0 then
associatedScroller.visibility = visibility.visible
else
associatedScroller.visibility = visibility.collapsed
end if
Is this possible to do and if so how do I do it?
Private Sub pnlDayScroller_Loaded(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles pnlDayScroller.Loaded
Dim binViewport, binMax, binMin, binSChange, binLChange As Binding
Dim horizontalScrollBar As Primitives.ScrollBar = CType(pnlDayScroller.Template.FindName("PART_HorizontalScrollBar", pnlDayScroller), Primitives.ScrollBar)
binViewport = New Binding("ViewportSize")
binViewport.Mode = BindingMode.OneWay
binViewport.Source = horizontalScrollBar
associatedScroller.SetBinding(Primitives.ScrollBar.ViewportSizeProperty, binViewport)
binMax = New Binding("Maximum")
binMax.Mode = BindingMode.OneWay
binMax.Source = horizontalScrollBar
associatedScroller.SetBinding(Primitives.ScrollBar.MaximumProperty, binMax)
binMin = New Binding("Minimum")
binMin.Mode = BindingMode.OneWay
binMin.Source = horizontalScrollBar
associatedScroller.SetBinding(Primitives.ScrollBar.MinimumProperty, binMin)
binSChange = New Binding("SmallChange")
binSChange.Mode = BindingMode.OneWay
binSChange.Source = horizontalScrollBar
associatedScroller.SetBinding(Primitives.ScrollBar.SmallChangeProperty, binSChange)
binLChange = New Binding("LargeChange")
binLChange.Mode = BindingMode.OneWay
binLChange.Source = horizontalScrollBar
associatedScroller.SetBinding(Primitives.ScrollBar.LargeChangeProperty, binLChange)
End Sub
Private Sub associatedScroller_Scroll(ByVal sender As System.Object, ByVal e As System.Windows.RoutedPropertyChangedEventArgs(Of Double)) Handles associatedScroller.ValueChanged
pnlDayScroller.ScrollToHorizontalOffset(e.NewValue)
end sub
FOLLOW UP (thanks to JustABill) :
I've add this code into the pnlDayScroller sub above (I've discovered scrollableWidth is a property of scrollviewer not scrollbar, but the maximum property gives a result I can use instead)
binVisibility = New Binding("Maximum")
binVisibility.Mode = BindingMode.OneWay
binVisibility.Source = horizontalScrollBar
binVisibility.Converter = New ScrollableConverter
associatedScroller.SetBinding(Primitives.ScrollBar.VisibilityProperty, binVisibility)
and I've created this class
Public Class ScrollableConverter
Implements IValueConverter
Public Function Convert(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object,
ByVal culture As System.Globalization.CultureInfo) As Object Implements IValueConverter.Convert
Dim dblMaximum As Double
If targetType IsNot GetType(Visibility) Then
Throw New InvalidOperationException("The target must be a visibility")
Else
dblMaximum = CType(value, Double)
Debug.WriteLine("Value of double is " & dblMaximum)
If dblMaximum > 0 Then
Return Visibility.Visible
Else
Return Visibility.Collapsed
End If
End If
End Function
Public Function ConvertBack(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object,
ByVal culture As System.Globalization.CultureInfo) As Object Implements IValueConverter.ConvertBack
Throw New NotSupportedException()
End Function
End Class
And the problem is resolved.
