xaml - How to format number of decimal places in wpf using style/template?

Question

I am writing a WPF program and I am trying to figure out a way to format data in a TextBox through some repeatable method like a style or template. I have a lot of TextBoxes (95 to be exact) and each one is bound to its own numeric data which can each have their own resolution defined. For example if the data is 99.123 with a resolution of 2 then it should display 99.12. Similarly a data value of 99 and resolution 3 should be displayed as 99.000 (not 99). Is there a way to do this?

Edit: I should clarify, there are 95 TextBoxes on the current screen I'm working on, but I want every TextBox throughout the various screens in my program to display the correct number of decimal places. Now that I think about it, some of these are TextBoxes (like the screen I'm working on now) and some are DataGrids or ListViews, but if I can figure out how to get it working for TextBoxes I'm sure I can figure it out for the other controls as well.

There's not much code to share in this case but I'll attempt to make it clearer:

I have a View Model which contains the following properties (vb.net):

    Public ReadOnly Property Resolution As Integer
        Get
            Return _signal.DisplayResolution
        End Get
    End Property

    Public ReadOnly Property Value As Single
        Get
            Return Math.Round(_signal.DisplayValue, Resolution)
        End Get
    End Property

and in the XAML I have:

<UserControl.Resources>
    <vm:SignalViewModel x:Key="Signal" SignalPath="SomeSignal"/>
</UserControl.Resources>
<TextBox Grid.Column="3" IsEnabled="False" Text="{Binding Path=Value, Source={StaticResource Signal}, Mode=OneWay}" />

EDIT2 (my solution): It turns out that after walking away from the computer for a while, I came back to find a simple answer that was staring me in the face. Format the data in the view model!

    Public ReadOnly Property Value As String
        Get
            Return (Strings.FormatNumber(Math.Round(_signal.DisplayValue, _signal.DisplayResolution), _signal.DisplayResolution))
        End Get
    End Property

Answer 1

You should use the StringFormat on the Binding. You can use either standard string formats, or custom string formats:

<TextBox Text="{Binding Value, StringFormat=N2}" />
<TextBox Text="{Binding Value, StringFormat={}{0:#,#.00}}" />

Note that the StringFormat only works when the target property is of type string. If you are trying to set something like a Content property (typeof(object)), you will need to use a custom StringFormatConverter (like here), and pass your format string as the ConverterParameter.

Edit for updated question

So, if your ViewModel defines the precision, I'd recommend doing this as a MultiBinding, and creating your own IMultiValueConverter. This is pretty annoying in practice, to go from a simple binding to one that needs to be expanded out to a MultiBinding, but if the precision isn't known at compile time, this is pretty much all you can do. Your IMultiValueConverter would need to take the value, and the precision, and output the formatted string. You'd be able to do this using String.Format.

However, for things like a ContentControl, you can much more easily do this with a Style:

<Style TargetType="{x:Type ContentControl}">
    <Setter Property="ContentStringFormat" 
            Value="{Binding Resolution, StringFormat=N{0}}" />
</Style>

Any control that exposes a ContentStringFormat can be used like this. Unfortunately, TextBox doesn't have anything like that.