CODEWITHSUNDEEP
wpfdata-bindingivalueconverter
Tom Davies
Tom Davies

Reputation: 2446

ValueConverter for IsChecked property of WPF Toggle Button

I'm trying to write a Value converter to use to bind the Boolean IsChecked property of a WPF ToggleButton to a non Boolean value (which happens to be a double) in my model. The convert function I've written looks like this:

        public object Convert(object value, Type targetType, object paramter, System.Globalization.CultureInfo culutre)
        {
          if (targetType != typeof(Boolean))
            throw new InvalidOperationException("Target type should be Boolean");

          var input = double.Parse(value.ToString());

          return (input==0.0) ? false: true;
        }

The problem is that when the funcion is invoked, the targetType is not what I expect - it's 

            "System.Nullable`1[[System.Boolean, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]"

Rather than System.Boolean. Is this expected? I've written other converters with no hassle in the past.

Upvotes: 4

Views: 3250

Answers (4)

Ashley Grenon
Ashley Grenon

Reputation: 9565

IsChecked is a nullable boolean. So instead of Boolean, check for bool?

Upvotes: 3

Robert Levy
Robert Levy

Reputation: 29073

Yes, IsChecked is a 'nullable' boolean... meaning it could be true, false, or null. It's pretty rare to have a toggle button with a null value here but more common on some of the subclasses like CheckBox.

Upvotes: 2

Adam Robinson
Adam Robinson

Reputation: 185583

This is as expected; IsChecked is a bool?, not a bool. Change your first line to this:

if (targetType != typeof(bool?))

Upvotes: 3

Martin Hennings
Martin Hennings

Reputation: 16846

Yes, since a ToggleButton (think of a checkbox) can be in three states: Checked, Unchecked and Neither (checkbox would be greyed out).

The MSDN library states:

ToggleButton Class
Base class for controls that can switch states, such as CheckBox.

and for IsChecked:

Property Value
Type: System.Nullable<Boolean>
true if the ToggleButton is checked; false if the ToggleButton is unchecked; otherwise null. The default is false.

So if you cast to a bool? or Nullable, you can easily get the value with .HasValue and .Value.

Upvotes: 5

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