WPF DataBinding with simple arithmetic operation?

Question

I want to add a constant value onto an incoming bound integer. In fact I have several places where I want to bind to the same source value but add different constants. So the ideal solution would be something like this...

<TextBox Canvas.Top="{Binding ElementName=mySource, Path=myInt, Constant=5}"/>
<TextBox Canvas.Top="{Binding ElementName=mySource, Path=myInt, Constant=8}"/>
<TextBox Canvas.Top="{Binding ElementName=mySource, Path=myInt, Constant=24}"/>

(NOTE: This is an example to show the idea, my actual binding scenario is not to the canvas property of a TextBox. But this shows the idea more clearly)

At the moment the only solution I can think of is to expose many different source properties each of which adds on a different constant to the same internal value. So I could do something like this...

<TextBox Canvas.Top="{Binding ElementName=mySource, Path=myIntPlus5}"/>
<TextBox Canvas.Top="{Binding ElementName=mySource, Path=myIntPlus8}"/>
<TextBox Canvas.Top="{Binding ElementName=mySource, Path=myIntPlus24}"/>

But this is pretty grim because in the future I might need to keep adding new properties for new constants. Also if I need to change the value added I need to go an alter the source object which is pretty naff.

There must be a more generic way than this? Any WPF experts got any ideas?

Answer 1

I use a MathConverterthat I created to do all simple arithmatic operations with. The code for the converter is here and it can be used like this:

<TextBox Canvas.Top="{Binding SomeValue, 
             Converter={StaticResource MathConverter},
             ConverterParameter=@VALUE+5}" />

You can even use it with more advanced arithmatic operations such as

Width="{Binding ElementName=RootWindow, Path=ActualWidth,
                Converter={StaticResource MathConverter},
                ConverterParameter=((@VALUE-200)*.3)}"