依赖属性安全性

项目
2025-05-07

通过 Windows Presentation Foundation （WPF）属性系统实现读写依赖属性的可访问性实际上使它们成为公共属性。因此，无法对读写依赖项属性值进行安全保证。 WPF 属性系统为只读依赖属性提供更多的安全性，以便限制写入访问。

属性包装器的访问和安全性

公共语言运行时（CLR）属性包装器通常包含在读写依赖属性实现中，以简化获取或设置属性值。如果包含，则 CLR 属性包装器是一种方便的方法，用于实现与基础依赖属性交互的静态调用 GetValue 和 SetValue。实质上，CLR 属性包装器将依赖属性公开为 CLR 属性，而该 CLR 属性由依赖属性支持，而非专用字段。

应用安全机制并限制对 CLR 属性包装器的访问可能会阻止使用便利方法，但这些技术不会阻止直接调用 GetValue 或 SetValue。换句话说，始终可通过 WPF 属性系统访问读写依赖属性。如果要实现读写依赖属性，请避免限制对 CLR 属性包装器的访问。相反，请将 CLR 属性包装器声明为公共成员，以便调用方知道依赖属性的真实访问级别。

依赖属性在属性系统中的暴露

WPF 属性系统通过其 DependencyProperty 标识符提供对读写依赖属性的访问权限。标识符在调用中GetValue SetValue可用。即使静态标识符字段是非公共的，属性系统的几个方面仍会返回它在类或派生类实例中的原样。例如，该方法 GetLocalValueEnumerator 返回具有本地设置值的依赖属性实例的标识符。此外，还可以重写 OnPropertyChanged 虚拟方法以接收事件数据，这些数据将报告 DependencyProperty 已更改值的依赖属性的标识符。若要让调用方了解读写依赖属性的真实访问级别，请将其标识符字段声明为公共成员。

注释

尽管将依赖属性标识符字段声明为 private 会减少访问读写依赖属性的途径，但根据 CLR 语言定义，该属性不会是私有的。

验证安全性

将Demand应用于ValidateValueCallback并预期Demand失败导致验证失败，这不是限制属性值更改的充分安全机制。此外，如果这些调用方在应用程序域内运行，恶意调用方可以抑制通过ValidateValueCallback执行的新值失效。

对只读依赖项属性的访问

若要限制访问，请通过调用 RegisterReadOnly 该方法将属性注册为只读依赖属性。该方法 RegisterReadOnly 返回一个 DependencyPropertyKey，你可以将其分配给非公共类字段。对于只读依赖属性，WPF 属性系统将仅向具有对的引用 DependencyPropertyKey的用户提供写入访问权限。为了说明此行为，请执行以下测试代码：

实例化实现读写和只读依赖项属性的类。
对每个标识符赋予private访问修饰符。
仅实现 get 访问器。
GetLocalValueEnumerator使用该方法通过 WPF 属性系统访问基础依赖属性。
调用 GetValue 并 SetValue 测试对每个依赖项属性值的访问。

    /// <summary>
    ///  Test get/set access to dependency properties exposed through the WPF property system.
    /// </summary>
    public static void DependencyPropertyAccessTests()
    {
        // Instantiate a class that implements read-write and read-only dependency properties.
        Aquarium _aquarium = new();
        // Access each dependency property using the LocalValueEnumerator method.
        LocalValueEnumerator localValueEnumerator = _aquarium.GetLocalValueEnumerator();
        while (localValueEnumerator.MoveNext())
        {
            DependencyProperty dp = localValueEnumerator.Current.Property;
            string dpType = dp.ReadOnly ? "read-only" : "read-write";
            // Test read access.
            Debug.WriteLine($"Attempting to get a {dpType} dependency property value...");
            Debug.WriteLine($"Value ({dpType}): {(int)_aquarium.GetValue(dp)}");
            // Test write access.
            try
            {
                Debug.WriteLine($"Attempting to set a {dpType} dependency property value to 2...");
                _aquarium.SetValue(dp, 2);
            }
            catch (InvalidOperationException e)
            {
                Debug.WriteLine(e.Message);
            }
            finally
            {
                Debug.WriteLine($"Value ({dpType}): {(int)_aquarium.GetValue(dp)}");
            }
        }

        // Test output:

        // Attempting to get a read-write dependency property value...
        // Value (read-write): 1
        // Attempting to set a read-write dependency property value to 2...
        // Value (read-write): 2

        // Attempting to get a read-only dependency property value...
        // Value (read-only): 1
        // Attempting to set a read-only dependency property value to 2...
        // 'FishCountReadOnly' property was registered as read-only
        // and cannot be modified without an authorization key.
        // Value (read-only): 1
    }
}

public class Aquarium : DependencyObject
{
    public Aquarium()
    {
        // Assign locally-set values.
        SetValue(FishCountProperty, 1);
        SetValue(FishCountReadOnlyPropertyKey, 1);
    }

    // Failed attempt to restrict write-access by assigning the
    // DependencyProperty identifier to a non-public field.
    private static readonly DependencyProperty FishCountProperty =
        DependencyProperty.Register(
          name: "FishCount",
          propertyType: typeof(int),
          ownerType: typeof(Aquarium),
          typeMetadata: new PropertyMetadata());

    // Successful attempt to restrict write-access by assigning the
    // DependencyPropertyKey to a non-public field.
    private static readonly DependencyPropertyKey FishCountReadOnlyPropertyKey =
        DependencyProperty.RegisterReadOnly(
          name: "FishCountReadOnly",
          propertyType: typeof(int),
          ownerType: typeof(Aquarium),
          typeMetadata: new PropertyMetadata());

    // Declare public get accessors.
    public int FishCount => (int)GetValue(FishCountProperty);
    public int FishCountReadOnly => (int)GetValue(FishCountReadOnlyPropertyKey.DependencyProperty);
}

    ''' <summary>
    ''' ' Test get/set access to dependency properties exposed through the WPF property system.
    ''' </summary>
    Public Shared Sub DependencyPropertyAccessTests()
        ' Instantiate a class that implements read-write and read-only dependency properties.
        Dim _aquarium As New Aquarium()
        ' Access each dependency property using the LocalValueEnumerator method.
        Dim localValueEnumerator As LocalValueEnumerator = _aquarium.GetLocalValueEnumerator()
        While localValueEnumerator.MoveNext()
            Dim dp As DependencyProperty = localValueEnumerator.Current.[Property]
            Dim dpType As String = If(dp.[ReadOnly], "read-only", "read-write")
            ' Test read access.
            Debug.WriteLine($"Attempting to get a {dpType} dependency property value...")
            Debug.WriteLine($"Value ({dpType}): {CInt(_aquarium.GetValue(dp))}")
            ' Test write access.
            Try
                Debug.WriteLine($"Attempting to set a {dpType} dependency property value to 2...")
                _aquarium.SetValue(dp, 2)
            Catch e As InvalidOperationException
                Debug.WriteLine(e.Message)
            Finally
                Debug.WriteLine($"Value ({dpType}): {CInt(_aquarium.GetValue(dp))}")
            End Try
        End While

        ' Test output

        ' Attempting to get a read-write dependency property value...
        ' Value (read-write): 1
        ' Attempting to set a read-write dependency property value to 2...
        ' Value (read-write): 2

        ' Attempting to get a read-only dependency property value...
        ' Value (read-only): 1
        ' Attempting to set a read-only dependency property value to 2...
        ' 'FishCountReadOnly' property was registered as read-only
        ' and cannot be modified without an authorization key.
        ' Value (read-only): 1
    End Sub

End Class

Public Class Aquarium
    Inherits DependencyObject

    Public Sub New()
        ' Assign locally-set values.
        SetValue(FishCountProperty, 1)
        SetValue(FishCountReadOnlyPropertyKey, 1)
    End Sub

    ' Failed attempt to restrict write-access by assigning the
    ' DependencyProperty identifier to a non-public field.
    Private Shared ReadOnly FishCountProperty As DependencyProperty =
        DependencyProperty.Register(
            name:="FishCount",
            propertyType:=GetType(Integer),
            ownerType:=GetType(Aquarium),
            typeMetadata:=New PropertyMetadata())

    ' Successful attempt to restrict write-access by assigning the
    ' DependencyPropertyKey to a non-public field.
    Private Shared ReadOnly FishCountReadOnlyPropertyKey As DependencyPropertyKey =
        DependencyProperty.RegisterReadOnly(
            name:="FishCountReadOnly",
            propertyType:=GetType(Integer),
            ownerType:=GetType(Aquarium),
            typeMetadata:=New PropertyMetadata())

    ' Declare public get accessors.
    Public ReadOnly Property FishCount As Integer
        Get
            Return GetValue(FishCountProperty)
        End Get
    End Property

    Public ReadOnly Property FishCountReadOnly As Integer
        Get
            Return GetValue(FishCountReadOnlyPropertyKey.DependencyProperty)
        End Get
    End Property

End Class

通过

依赖属性安全性

属性包装器的访问和安全性

依赖属性在属性系统中的暴露

验证安全性

对只读依赖项属性的访问

另请参阅

其他资源