DependencyPropertyChangedEventArgs 结构

定义

命名空间:

System.Windows

程序集:

WindowsBase.dll

提供各种属性更改事件的数据。 通常这些事件对只读依赖属性的值中的有效值更改进行报告。 另一个用法是用作 PropertyChangedCallback 实现的一部分。

public value class DependencyPropertyChangedEventArgs

public struct DependencyPropertyChangedEventArgs

type DependencyPropertyChangedEventArgs = struct

Public Structure DependencyPropertyChangedEventArgs

继承

Object

ValueType

DependencyPropertyChangedEventArgs

示例

下面的示例在 DependencyPropertyChangedEventArgs 的上下文 PropertyChangedCallback 中使用 类，用于自定义类的特定属性，该属性也定义了事件。 回调从属性系统中获取由 传达 DependencyPropertyChangedEventArgs的新旧值的结果，并将这些结果重新打包到不同的事件参数类 RoutedPropertyChangedEventArgs<T>中。 然后，新参数用作自定义类定义和引发的“ValueChanged”事件的数据。

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);
}

Public Shared ReadOnly ValueProperty As DependencyProperty = DependencyProperty.Register("Value", GetType(Decimal), GetType(NumericUpDown), New FrameworkPropertyMetadata(MinValue, New PropertyChangedCallback(AddressOf OnValueChanged), New CoerceValueCallback(AddressOf CoerceValue)))

Private Shared Overloads Function CoerceValue(ByVal element As DependencyObject, ByVal value As Object) As Object
    Dim newValue As Decimal = CDec(value)

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

    Return newValue
End Function

Private Shared Sub OnValueChanged(ByVal obj As DependencyObject, ByVal args As DependencyPropertyChangedEventArgs)
    Dim control As NumericUpDown = CType(obj, NumericUpDown)

    Dim e As New RoutedPropertyChangedEventArgs(Of Decimal)(CDec(args.OldValue), CDec(args.NewValue), ValueChangedEvent)
    control.OnValueChanged(e)
End Sub
''' <summary>
''' Identifies the ValueChanged routed event.
''' </summary>
Public Shared ReadOnly ValueChangedEvent As RoutedEvent = EventManager.RegisterRoutedEvent("ValueChanged", RoutingStrategy.Bubble, GetType(RoutedPropertyChangedEventHandler(Of Decimal)), GetType(NumericUpDown))

''' <summary>
''' Occurs when the Value property changes.
''' </summary>
Public Custom Event ValueChanged As RoutedPropertyChangedEventHandler(Of Decimal)
    AddHandler(ByVal value As RoutedPropertyChangedEventHandler(Of Decimal))
        MyBase.AddHandler(ValueChangedEvent, value)
    End AddHandler
    RemoveHandler(ByVal value As RoutedPropertyChangedEventHandler(Of Decimal))
        MyBase.RemoveHandler(ValueChangedEvent, value)
    End RemoveHandler
    RaiseEvent(ByVal sender As System.Object, ByVal e As RoutedPropertyChangedEventArgs(Of Decimal))
    End RaiseEvent
End Event
''' <summary>
''' Raises the ValueChanged event.
''' </summary>
''' <param name="args">Arguments associated with the ValueChanged event.</param>
Protected Overridable Sub OnValueChanged(ByVal args As RoutedPropertyChangedEventArgs(Of Decimal))
    MyBase.RaiseEvent(args)
End Sub

注解

对事件数据使用 DependencyPropertyChangedEventArgs 类的事件和 DependencyPropertyChangedEventHandler 处理程序的方法实现通常遵循命名模式 Is*Changed，并且通常作为公共语言运行时 (CLR) 事件实现，而不 RoutedEvent (它们不是路由事件) 。 某些类处理方法“处理”通过属性更改报告状态更改的未公开事件，例如 ButtonBase.OnIsPressedChanged，也对事件数据使用 DependencyPropertyChangedEventArgs 类。

的方案 PropertyChangedCallback 是使用 参数来报告来自属性的属性系统评估中的旧值和新值。 处理新旧值的回调可能会根据这些值选择特殊处理，例如选择不响应被视为微不足道的值更改。

构造函数

DependencyPropertyChangedEventArgs(DependencyProperty, Object, Object)

初始化 DependencyPropertyChangedEventArgs 类的新实例。

属性

NewValue	获取发生更改之后的属性的值。
OldValue	获取发生更改之前的属性的值。
Property	获取发生值更改的依赖项属性的标识符。

方法

Equals(DependencyPropertyChangedEventArgs)	确定提供的 DependencyPropertyChangedEventArgs 是否与当前 DependencyPropertyChangedEventArgs 相同。
Equals(Object)	确定提供的对象是否与当前 DependencyPropertyChangedEventArgs 相同。
GetHashCode()	获取此 DependencyPropertyChangedEventArgs 的哈希代码。

运算符

Equality(DependencyPropertyChangedEventArgs, DependencyPropertyChangedEventArgs)	确定两个指定的 DependencyPropertyChangedEventArgs 对象是否具有相同的值。
Inequality(DependencyPropertyChangedEventArgs, DependencyPropertyChangedEventArgs)	确定两个指定的 DependencyPropertyChangedEventArgs 对象是否不同。

另请参阅

• DependencyPropertyChangedEventHandler