Question

When you format a TextBox as currency and click to edit it, the $ and commas do not cause a problem, you can just edit and tab with no problem. When you format a field as a percentage things do not work so well.

<TextBox Text="{Binding CostMarkup, 
                         StringFormat=P}"
                Style="{StaticResource ctrlSpacingTight}" />

If the underlying value is 0.1 it correctly displays as 10%, if you go to edit it still shows as 10% the % will cause a problem plus it will change the underlying value from .1 to 10. I wrote a Converter to handle all this but I’m wondering if there isn’t a better way. In particular is there a way to handle it the way currency handles it?

There is a built in currency converter so I suspect the currency version of StringFormat uses that. While there is a ZoomPerentageConverter it doesn’t do what I would expect. Is there a way to hook in to StringFormat=P and have it invoke my Converter instead of having to go to every instance and explicitly specify it?

<TextBox Text="{Binding CostMarkup, 
                         StringFormat=P,
                         Converter={StaticResource pctConverter}}"
                Style="{StaticResource ctrlSpacingTight}" />

Answer 1

I’ve always found that it’s easiest to display the raw data when editing, and the formatted value when not.

Here’s an example that does that using a trigger

<Style x:Key="ctrlSpacingTight" TargetType="{x:Type TextBox}">
    <!-- Other Style Setters -->
    <Setter Property="Text" Value="{Binding CostMarkup, StringFormat={}{0:C}}" />
    <Style.Triggers>
        <Trigger Property="IsKeyboardFocused" Value="True">
            <Setter Property="Text" Value="{Binding CostMarkup}" />
        </Trigger>
    </Style.Triggers>
</Style>

If ctrlSpacingTight is a global style, you can create a style for your TextBox that is BasedOn your global style.

<Style x:Key="CurrencyTextBox" TargetType="{x:Type TextBox}"
       BasedOn="{StaticResource ctrlSpacingTight}">
    <Setter Property="Text" Value="{Binding CostMarkup, StringFormat={}{0:C}}" />
    <Style.Triggers>
        <Trigger Property="IsKeyboardFocused" Value="True">
            <Setter Property="Text" Value="{Binding CostMarkup}" />
        </Trigger>
    </Style.Triggers>
</Style>