Dependency Property Used in WPF

Question

It's hard for me to identify good reasons for a dependency property. Why is the System.Controls.TextBox “Text” property a dependency property rather than a normal property? What benefits does it serve as a dependency property?

One of the things I'm trying to accomplish is to add the ValidationRules property to my UserControl, which will contain other validation rules. Like here:

<customControls:RequiredTextBox.ValidationRules>
                        <validators:NotNullOrEmptyValidationRule ErrorMessage="FirstName cannot be null or empty"/>
                    </customControls:RequiredTextBox.ValidationRules>

The problem is that I'm not sure if the ValidationRules property should be a DependencyProperty or just a normal property.

The above code gives the following error:

{"Cannot add element to 'ValidationRules'; the property value is null.  Error at object 'LearningWPF.ValidationRules.NotNullOrEmptyValidationRule' in markup file 'LearningWPF;component/addcustomerwindow.xaml' Line 35 Position 66."}

Here is the ValidationRules property:

 public static readonly DependencyProperty ValidationRulesProperty =
            DependencyProperty.Register("ValidationRules",
                                        typeof (Collection<ValidationRule>), typeof (RequiredTextBox),
                                        new FrameworkPropertyMetadata(null)); 

        public Collection<ValidationRule> ValidationRules
        {
            get { return (Collection<ValidationRule>)GetValue(ValidationRulesProperty); }
            set { SetValue(ValidationRulesProperty, value); }
        }

Answer 1

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