Convert int textbox input to negative in xaml?

Question

I have a textbox where the user enters in a number that is to be used as the angle to rotate an image. Is there a way to convert that number in xaml to negative? So if the user enters 50, I want the image to rotate -50 degrees instead of +50. I'd rather not do it in the code-behind. Code for it is below:

<TextBox x:Name="testing" />

 <Image Source="aaaa.png" x:Name="thisimage" >
    <Image.LayoutTransform>
        <RotateTransform CenterX="0.5" CenterY="0.5"  Angle="{Binding Path=Text , ElementName=testing, UpdateSourceTrigger=PropertyChanged}" />
    </Image.LayoutTransform>
 </Image>

Would a ValueConverter be acceptable or are you looking for XAML only solutions? A ValueConverter is code, but not "code behind" — default, Feb 16 '15 at 17:52
Well, I'd like a XAML only solution just because I'm trying to get out of the habit of doing so much in C# with twice the amount of code. But if it's not possible or too much trouble then I could do a valueconverter. — pfinferno, Feb 16 '15 at 17:57
there's a good thread [here](http://stackoverflow.com/questions/2580467/wpf-property-data-binding-to-negate-the-property) describing ValuConverters, and a second solution, simply `NegatedText { get { return -Text; } }` which I actually think is the easiest solution. When I think about it, I don't think there is any solution without writing *any* code. — default, Feb 16 '15 at 18:09

Clemens · Accepted Answer · 2015-02-16T18:24:30.040

2

This would be a pure XAML solution:

<Image.LayoutTransform>
    <TransformGroup>
        <ScaleTransform ScaleX="-1"/>
        <RotateTransform CenterX="0.5" CenterY="0.5"
            Angle="{Binding Path=Text, ElementName=testing,
                            UpdateSourceTrigger=PropertyChanged}" />
        <ScaleTransform ScaleX="-1"/>
    </TransformGroup>
</Image.LayoutTransform>

I would still recommend using a binding converter.

edited Feb 16 '15 at 18:24

answered Feb 16 '15 at 18:17

Clemens

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This is what I was looking for. The other answers/comments helped though, I'm looking into converters now. – pfinferno Feb 16 '15 at 18:25

score 1 · Answer 2 · answered Feb 16 '15 at 18:07

Try following code.

Firstly create implementing IValueConverter:

public class AngleConverter:IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        var angle = (int)value;

        if (angle != null)
        {
            return -angle;
        }

        return null;
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        throw new NotImplementedException();
    }
}

XAML:

<TextBox x:Name="testing" />
<Image Source="aaaa.png" x:Name="thisimage" >
<Image.LayoutTransform>
    <RotateTransform CenterX="0.5" CenterY="0.5"  Angle="{Binding Path=Text , ElementName=testing, Converter={StaticResource angleConverter} UpdateSourceTrigger=PropertyChanged}" />
</Image.LayoutTransform>

Add reference to your converter:

xmlns:cr="using:[project].Converters"

Don't forget add to resource:

<UserControl.Resources>
    <cr:AngleConverter x:Key="angleConverter"/>
</UserControl.Resources>

It seems the method is incorrectly implemented according to the [documentation](https://msdn.microsoft.com/en-us/library/system.windows.data.ivalueconverter.convert%28v=vs.110%29.aspx). It shouldn't be `(object, Type, object, string)`, but `(object, Type, object, CultureInfo)` — default, Feb 16 '15 at 18:12
@Default Depends on the platform. Here, it's the correct implementation for Windows Runtime, although the question was for WPF. The XAML namespace declaration `xmlns:cr="using:..."` is also Windows Runtime. — Clemens, Feb 16 '15 at 18:13

Convert int textbox input to negative in xaml?

2 Answers2