C# 4 and .NET 4

734 ❘ ChaPTer 27 COre xAml
}
set { SetValue(ValueProperty, value); }
}
}
public static readonly DependencyProperty ValueProperty =
DependencyProperty.Register("Value", typeof(int), typeof(MyDependencyObject));
public int Minimum
{
get { return (int)GetValue(MinimumProperty); }
set { SetValue(MinimumProperty, value); }
}
public static readonly DependencyProperty MinimumProperty =
DependencyProperty.Register("Minimum", typeof(int), typeof(MyDependencyObject),
new PropertyMetadata(0));
public int Maximum
{
get { return (int)GetValue(MaximumProperty); }
set { SetValue(MaximumProperty, value); }
}
public static readonly DependencyProperty MaximumProperty =
DependencyProperty.Register("Maximum", typeof(int), typeof(MyDependencyObject),
new PropertyMetadata(100));
code snippet DependencyObjectDemo/MyDependencyObject.cs
W i t hi n t he get and set property accessors you may not do more than just calling the
GetValue() and SetValue() methods. Using the dependency properties, the property
values can be accessed from the outside with the GetValue() and SetValue() methods,
which is also done from WPF, and thus, the strongly - typed property accessors might not
be invoked at all. They are just here for convenience for custom code.
Coerce Value Callback
Dependency properties support coercion. With coercion, the value of the property can be checked to see if
it is valid, for example, that it falls within a valid range. That ’ s why the Minimum and Maximum properties
are included in the sample. Now the registration of the Value property is changed to pass the event handler
method CoerceValue() to the constructor of PropertyMetadata , which is passed as an argument to
the DependencyProperty.Register() method. The CoerceValue() method is now invoked with every
change of the property value from the implementation of the SetValue() method. Within CoerceValue() ,
the set value is checked to see if it falls within the range between the minimum and maximum, and the
value is set accordingly if this is not the case.
using System;
using System.Windows;
namespace Wrox.ProCSharp.XAML
{
class MyDependencyObject : DependencyObject
{
public int Value
{
get { return (int)GetValue(ValueProperty); }
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