wpf binding property in ValidationRule - wpf

Question

i'm having a form with 2 text boxes:
TotalLoginsTextBox
UploadsLoginsTextBox
i want to limit UploadsLoginsTextBox so the maximum input for the text will be the value of the TotalLoginsTextBox.
i am also using a value converter so i try to bound the Maximum value:
this is the XAML:
<!-- Total Logins -->
<Label Margin="5">Total:</Label>
<TextBox Name="TotalLoginsTextBox" MinWidth="30" Text="{Binding Path=MaxLogins, Mode=TwoWay}" />
<!-- Uploads -->
<Label Margin="5">Uploads:</Label>
<TextBox Name="UploadsLoginsTextBox" MinWidth="30">
<TextBox.Text>
<Binding Path="MaxUp" Mode="TwoWay" NotifyOnValidationError="True">
<Binding.ValidationRules>
<Validators:MinMaxRangeValidatorRule Minimum="0" Maximum="{Binding Path=MaxLogins}" />
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
the problem i am getting the following error:
A 'Binding' cannot be set on the 'Maximum' property of type
'MinMaxRangeValidatorRule'. A 'Binding' can only be set on a
DependencyProperty of a DependencyObject.
what is the proper way to do the binding ?

Answer 1

You're seeing this error because MinMaxRangeValidatorRule.Maximum needs to be a DependencyProperty if you want to bind it to MaxLogins, while it is probably a simple CLR property.
The real problem is that MinMaxRangeValidatorRule should be able to inherit from ValidationRule AND from DependencyObject (to make Dependency Properties available). This is not possible in C#.
I solved a similar problem in this way:
give a name to your validator rule
<Validators:MinMaxRangeValidatorRule Name="MinMaxValidator" Minimum="0" />
in code behind, set the Maximum value whenever MaxLogins changes
public int MaxLogins
{
get { return (int )GetValue(MaxLoginsProperty); }
set { SetValue(MaxLoginsProperty, value); }
}
public static DependencyProperty MaxLoginsProperty = DependencyProperty.Register("MaxLogins ",
typeof(int),
typeof(mycontrol),
new PropertyMetadata(HandleMaxLoginsChanged));
private static void HandleMinValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
mycontrol source = (mycontrol) d;
source.MinMaxValidator.Maximum = (int) e.NewValue;
}

Answer 2

I'm guessing the "MinMaxRangeValidatorRule" is something custom.
The error message is quite explicit actually, you need to make the "Maximum" variable a Dependency Property, like so:
public int Maximum
{
get { return (int)GetValue(MaximumProperty); }
set { SetValue(MaximumProperty, value); }
}
// Using a DependencyProperty as the backing store for Maximum. This enables animation, styling, binding, etc...
public static readonly DependencyProperty MaximumProperty =
DependencyProperty.Register("Maximum", typeof(int), typeof(MinMaxRangeValidatorRule), new UIPropertyMetadata(0));
You can access the dependency property snippet by typing "propdp" in vs2010.