Wpf – Make checkbox bound to nullable bool transition from null to true

bindingcheckboxwpf

I have a checkbox with its IsChecked property bound to a nullable bool. When my control first loads the value is null and the checkbox appears greyed out. This is what I want.

When the user clicks the checkbox, it moves to the false/Unchecked state.

However, 99% of the time the user is going to want to tick the checkbox – which currently means double clicking the checkbox.

How can I make the value move from null to true when the user first clicks the checkbox?

Best Answer

You can just modify the setter of the bound property to check whether the previous value is null and if it is, set the value to true. Something like this:

public bool? MyBoolProperty 
{
   get { return _myBoolProperty; }
   set 
   {
       _myBoolProperty = (_myBoolProperty != null || value == null) ? value : true;
       RaisePropertyChanged("MyBoolProperty");       
   }
}

The binding system will re-read the property after it sets it, so the new value will be reflected by the CheckBox.

Related Solutions

C# – A read-only CheckBox in C# WPF

What about data binding to the IsHitTestVisible property?

For example, assuming an MVVM approach:

Add a IsReadOnly property to your view model, initially set as true to allow click.
Binding this property to CheckBox.IsHitTestVisible.
After the first click, update your view model to set this value to false, preventing any further clicks.

I don't have this exact requirement, I just needed an always read only checkbox, and it seems to solve the problem nicely. Also note Goran's comment below about the Focusable property.

Wpf – Bound Property always returns false but WPF bound CheckBox is still checked

I remember having a very similar problem, but I can't find where and how I solved it. I thought that the problem was caused by how WPF updates bindings, and I thought that I read somewhere that it could be solved by using an IValueConverter that simply passes the values through, but I've tested that it and it doesn't seem to work. It was supposed to work because using a converter was supposed to make the bindings re-evaluate.

You could always handle the Clicked event on the CheckBox and update the values via code, but it just feels so dirty. Sorry I couldn't be of more help

<StackPanel.Resources>
    <local:PassThroughConverter x:Key="PassThroughConverter" />
</StackPanel.Resources>
<CheckBox IsChecked="{Binding IsExistingTemplate, Converter={StaticResource PassThroughConverter}}" Content="Stuff"/>

public class PassThroughConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value;
    }

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

Best Answer

Related Solutions

C# – A read-only CheckBox in C# WPF

Wpf – Bound Property always returns false but WPF bound CheckBox is still checked

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