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DependencyPropertyChangedEventArgs Structure

Provides data for various property changed events. Typically these events report effective value changes in the value of a read-only dependency property. Another usage is as part of a PropertyChangedCallback implementation.

Namespace:  System.Windows
Assembly:  WindowsBase (in WindowsBase.dll)

public struct DependencyPropertyChangedEventArgs

The DependencyPropertyChangedEventArgs type exposes the following members.

  NameDescription
Public methodDependencyPropertyChangedEventArgsInitializes a new instance of the DependencyPropertyChangedEventArgs class.
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  NameDescription
Public propertyNewValueGets the value of the property after the change.
Public propertyOldValueGets the value of the property before the change.
Public propertyPropertyGets the identifier for the dependency property where the value change occurred.
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  NameDescription
Public methodEquals(DependencyPropertyChangedEventArgs)Determines whether the provided DependencyPropertyChangedEventArgs is equivalent to the current DependencyPropertyChangedEventArgs.
Public methodEquals(Object)Determines whether the provided object is equivalent to the current DependencyPropertyChangedEventArgs. (Overrides ValueType.Equals(Object).)
Public methodGetHashCodeGets a hash code for this DependencyPropertyChangedEventArgs. (Overrides ValueType.GetHashCode().)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodToStringReturns the fully qualified type name of this instance. (Inherited from ValueType.)
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  NameDescription
Public operatorStatic memberEqualityDetermines whether two specified DependencyPropertyChangedEventArgs objects have the same value.
Public operatorStatic memberInequalityDetermines whether two specified DependencyPropertyChangedEventArgs objects are different.
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The events that use the DependencyPropertyChangedEventArgs class for event data, and the DependencyPropertyChangedEventHandler method implementations for handlers, generally follow the naming pattern Is*Changed, and are generally implemented as common language runtime (CLR) events without RoutedEvent backing (they are not routed events). Some class handling methods that "handle" otherwise unexposed events that report a state change through a property change, such as ButtonBase.OnIsPressedChanged, also use the DependencyPropertyChangedEventArgs class for event data.

The scenario for PropertyChangedCallback is to use the arguments to report old and new values that come from the property system evaluation of the property. A callback that processes old and new values might choose special handling depending on these values, such as choosing to not respond to value changes that are deemed insignificant.

The following example uses the DependencyPropertyChangedEventArgs class in the context of a PropertyChangedCallback for a particular property of a custom class that also defines events. The callback takes the results of old and new values from the property system as communicated by DependencyPropertyChangedEventArgs, and repackages these into a different events arguments class RoutedPropertyChangedEventArgs<T>. The new arguments are then used as the data for a "ValueChanged" event defined by and raised by the custom class.

public static readonly DependencyProperty ValueProperty =
    DependencyProperty.Register(
        "Value", typeof(decimal), typeof(NumericUpDown),
        new FrameworkPropertyMetadata(MinValue, new PropertyChangedCallback(OnValueChanged),
                                      new CoerceValueCallback(CoerceValue)));

private static object CoerceValue(DependencyObject element, object value)
{
    decimal newValue = (decimal)value;

    newValue = Math.Max(MinValue, Math.Min(MaxValue, newValue));

    return newValue;
}

private static void OnValueChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
    NumericUpDown control = (NumericUpDown)obj;

    RoutedPropertyChangedEventArgs<decimal> e = new RoutedPropertyChangedEventArgs<decimal>(
        (decimal)args.OldValue, (decimal)args.NewValue, ValueChangedEvent);
    control.OnValueChanged(e);
}
/// <summary> 
/// Identifies the ValueChanged routed event. 
/// </summary> 
public static readonly RoutedEvent ValueChangedEvent = EventManager.RegisterRoutedEvent(
    "ValueChanged", RoutingStrategy.Bubble,
    typeof(RoutedPropertyChangedEventHandler<decimal>), typeof(NumericUpDown));

/// <summary> 
/// Occurs when the Value property changes. 
/// </summary> 
public event RoutedPropertyChangedEventHandler<decimal> ValueChanged
{
    add { AddHandler(ValueChangedEvent, value); }
    remove { RemoveHandler(ValueChangedEvent, value); }
}
/// <summary> 
/// Raises the ValueChanged event. 
/// </summary> 
/// <param name="args">Arguments associated with the ValueChanged event.</param>
protected virtual void OnValueChanged(RoutedPropertyChangedEventArgs<decimal> args)
{
    RaiseEvent(args);
}

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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