程序绑定控件中的算术

Question

I want to set the binding of programmatically created control with arithmetic involved. Here as example of the XAML of what I am trying to do using the extension "qc":

<ColumnDefinition x:Name="MidColumn" 
      Width="{qc:Binding '$P * .727', P={Binding ActualHeight, ElementName=PaperCanvas}}" />

Here's an example of what I'm trying to do in the actual code:

Binding binding = new Binding();
//Below is pseudo code for what i'm trying to do
binding.Path = new PropertyPath(Canvas.ActualWidthProperty * 0.7);
binding.Source = TrueCanvas;
binding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
BindingOperations.SetBinding(((Rectangle)CurrentControl), Rectangle.WidthProperty, binding);

I've looked into using a Grid so I can set the Width and Height as a percentage using GridUnitType.Star , but with where I'm at as it is, it would more than likely cause more harm than good, so I'm trying to just bite the bullet and see if I can get it done this way.

Answer 1

That "qc" syntax does not look like a converter, but rather a markup extension. If you want to use an IValueConverter (which does seem best), then you simply add it to the binding.

binding.Path = new PropertyPath(Canvas.ActualWidthProperty);
binding.Converter = new WidthConverter();

The converter code should look something like this:

public class WidthConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        var x = (double)value;
        return x * 0.7;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

(If for some reason you did actually need to use that custom "qc" Binding as in your XAML excerpt, then you would probably just need to set that "formula" property, whatever its name is, in the code.)