Bind a formula to a TextBox - wpf

Question

I'm doing a little program that needs to calculate the thickness of a book using its page count.
Please note that I'm almost completely new to programing. And this is my first time on ths website.
Here's the XAML.
<StackPanel VerticalAlignment="Center" Margin="25 5 0 10">
<Slider Maximum="800" TickPlacement="BottomRight" TickFrequency="1"
IsSnapToTickEnabled="True" DockPanel.Dock="Right" x:Name="slNumPages"
Margin="0" LargeChange="16" SmallChange="2" Value="200" Minimum="16"
BorderThickness="0" />
<WrapPanel>
<TextBox Text="{Binding ElementName=slNumPages, Path=Value,
UpdateSourceTrigger=PropertyChanged}" Width="40" />
<TextBlock Text="Approx. thickness: " />
<TextBlock x:Name="tbApproxThickness" Text="..."/>
</WrapPanel>
How can I bind the TextBlock tbApproxThickness to a formula where the value of slider slNumPages gets multiplied by constant 0.0252?

Answer 1

here you go
<StackPanel VerticalAlignment="Center"
Margin="25 5 0 10"
xmlns:l="clr-namespace:CSharpWPF">
<StackPanel.Resources>
<l:ApproxThicknessConverter x:Key="ApproxThicknessConverter" />
</StackPanel.Resources>
<Slider Maximum="800"
TickPlacement="BottomRight"
TickFrequency="1"
IsSnapToTickEnabled="True"
DockPanel.Dock="Right"
x:Name="slNumPages"
Margin="0"
LargeChange="16"
SmallChange="2"
Value="200"
Minimum="16"
BorderThickness="0" />
<WrapPanel>
<TextBox Text="{Binding ElementName=slNumPages, Path=Value,
UpdateSourceTrigger=PropertyChanged}"
Width="40" />
<TextBlock Text="Approx. thickness: " />
<TextBlock x:Name="tbApproxThickness"
Text="{Binding Value,ElementName=slNumPages,Converter={StaticResource ApproxThicknessConverter}}" />
</WrapPanel>
</StackPanel>
following are the changed for the same
<l:ApproxThicknessConverter x:Key="ApproxThicknessConverter" />
Text="{Binding Value,ElementName=slNumPages,Converter={StaticResource ApproxThicknessConverter}}"
converter class
namespace CSharpWPF
{
class ApproxThicknessConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return (double)value * 0.0252;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
}

Answer 2

You may need to refer to the Data Binding Overview page on MSDN to understand this answer. One simple solution would be to data bind a double property to the Slider.Value property and then reference this property in a formula property that does the calculation. Try something like this:
public double SliderValue
{
get { return sliderValue; }
set
{
sliderValue = value;
NotifyPropertyChanged("SliderValue"); // Implement INotifyPropertyChanged
FormulaValue = sliderValue * 0.0252;
}
}
public double FormulaValue { get; set; } // Implement INotifyPropertyChanged
...
<Slider Maximum="800" TickPlacement="BottomRight" TickFrequency="1"
IsSnapToTickEnabled="True" DockPanel.Dock="Right" x:Name="slNumPages"
Margin="0" LargeChange="16" SmallChange="2" Value="{Binding SliderValue}"
Minimum="16" BorderThickness="0" />
<WrapPanel>
<TextBox Text="{Binding ElementName=slNumPages, Path=Value,
UpdateSourceTrigger=PropertyChanged}" Width="40" />
<TextBlock Text="Approx. thickness: " />
<TextBlock x:Name="tbApproxThickness" Text="{Binding FormulaValue}" />
</WrapPanel>
Please bear in mind that you will need to implement the INotifyPropertyChanged Interface on these properties to make this work. You will also need to set the DataContext of the Window properly. Having done that, each time the Slider is moved, the property will automatically update the FormulaValue.