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c#wpf
Martyn Ball
Martyn Ball

Reputation: 4885

c# Converter getting Specified cast is not valid

I'm trying to simply do some Math on my custom control. I need to take a "Width" value and divide it by the Converter Paramater.

Here is the Binding:

<Border x:Name="circleBorder"
     Grid.Row="0"
     CornerRadius="{Binding Path=ActualWidth, ElementName=circleGrid}"
     Width="{Binding Path=ActualWidth, ElementName=circleGrid}"
     Height="{Binding Path=ActualWidth, ElementName=circleGrid}"
     BorderBrush="White"
     BorderThickness="{Binding Converter={StaticResource CalculateBorder}, Path=Width, ElementName=circleBorder, ConverterParameter=30}">

And this is the converter, which should do some simple Math.

public class CalculateBorder : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {   
        return ((double)value / (double)parameter);
    }
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

I'm getting this error on return ((double)value / (double)parameter);:

Specified cast is not valid.

Upvotes: 1

Views: 4870

Answers (3)

Jens
Jens

Reputation: 2702

The problem is that it is not possible to unbox parameter because in this case parameter is a string.

The solution is converting the parameter to double with the Convert class

var yourDouble = Convert.ToDouble(parameter);

The problem of the above code is that Convert is defined as your Convert method of the IValueConverter. So you need to specify the full namespace by adding System. The complete expression looks like this:

var yourDouble = System.Convert.ToDouble(parameter);

to make clear to the compiler that you want to use the System.Convert class

Moreover the property BorderThickness has the type Thickness. so you should return a Thickness object reference instead of a double.

Upvotes: 8

Abin
Abin

Reputation: 2956

You have to return System.Windows.Thickness like below,

 public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
 {           
    return new Thickness(10,10,10,10);
 }

The BorderThickness accepts System.Windows.Thickness

The converter parameter value gives the object of Thickness class so you need to convert it to match your logic.

MSDN

public System.Windows.Thickness BorderThickness { get; set; }

Member of System.Windows.Controls.Border

Summary: Gets or sets the relative System.Windows.Thickness of a System.Windows.Controls.Border.

Returns: The System.Windows.Thickness that describes the width of the boundaries of the System.Windows.Controls.Border. This property has no default value.

Upvotes: 2

Henryk Budzinski
Henryk Budzinski

Reputation: 1293

object parameter is an string

return ((double)value / Convert.ToDouble(parameter));

Upvotes: 2

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