使用 INotifyPropertyChanged 绑定到 Silverlight 中的字典

Question

在 silverlight 中，我无法让 INotifyPropertyChanged 在绑定到字典时像我希望的那样工作。在下面的示例中，页面可以绑定到字典，但是当我更改其中一个文本框的内容时，不会调用 CustomProperties 属性设置器。 CustomProperties 属性设置器仅在设置 CustomProperties 时调用，而不是在设置其中的值时调用。我正在尝试对字典值进行一些验证，因此希望在字典中的每个值发生更改时运行一些代码。有什么我可以在这里做的吗？

C#

public partial class MainPage : UserControl
{

    public MainPage()
    {
        InitializeComponent();

        MyEntity ent = new MyEntity();
        ent.CustomProperties.Add("Title", "Mr");
        ent.CustomProperties.Add("FirstName", "John");
        ent.CustomProperties.Add("Name", "Smith");

        this.DataContext = ent;
    }

}

public class MyEntity : INotifyPropertyChanged
{

    public event PropertyChangedEventHandler System.ComponentModel.INotifyPropertyChanged.PropertyChanged;
    public delegate void PropertyChangedEventHandler(object sender, System.ComponentModel.PropertyChangedEventArgs e);

    private Dictionary<string, object> _customProps;
    public Dictionary<string, object> CustomProperties {
        get {
            if (_customProps == null) {
                _customProps = new Dictionary<string, object>();
            }
            return _customProps;
        }
        set {
            _customProps = value;
            if (PropertyChanged != null) {
                PropertyChanged(this, new PropertyChangedEventArgs("CustomProperties"));
            }
        }
    }

}

VB

Partial Public Class MainPage
    Inherits UserControl

    Public Sub New()
        InitializeComponent()

        Dim ent As New MyEntity
        ent.CustomProperties.Add("Title", "Mr")
        ent.CustomProperties.Add("FirstName", "John")
        ent.CustomProperties.Add("Name", "Smith")

        Me.DataContext = ent
    End Sub

End Class

Public Class MyEntity
    Implements INotifyPropertyChanged

    Public Event PropertyChanged(ByVal sender As Object, ByVal e As System.ComponentModel.PropertyChangedEventArgs) Implements System.ComponentModel.INotifyPropertyChanged.PropertyChanged

    Private _customProps As Dictionary(Of String, Object)
    Public Property CustomProperties As Dictionary(Of String, Object)
        Get
            If _customProps Is Nothing Then
                _customProps = New Dictionary(Of String, Object)
            End If
            Return _customProps
        End Get
        Set(ByVal value As Dictionary(Of String, Object))
            _customProps = value
            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs("CustomProperties"))
        End Set
    End Property

End Class

Xaml

<TextBox Height="23" Name="TextBox1" Text="{Binding Path=CustomProperties[Title], Mode=TwoWay}" />
<TextBox Height="23" Name="TextBox2" Text="{Binding Path=CustomProperties[FirstName], Mode=TwoWay}" />
<TextBox Height="23" Name="TextBox3" Text="{Binding Path=CustomProperties[Name], Mode=TwoWay}" />

Answer 1

这是一个（有些过于简单化的）解决方案。

public class MyEntity : INotifyPropertyChanged
{

    public event PropertyChangedEventHandler PropertyChanged;

    private readonly Dictionary<string, object> _customProps = new Dictionary<string, object>();

    public void AddCustomProperty(string key, object value)
    {
        _customProps.Add(key, value);
    }

    public object this[string key]
    {
        get { return _customProps[key]; }
        set
        {
            // The validation code of which you speak here.
            _customProps[key] = value;
            NotifyPropertyChanged("Item[" + key "]");
        }
    }

    private void NotifyPropertyChanged(string name)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(name));
    }
}

主页：-

    public MainPage()
    {
        InitializeComponent();

        MyEntity ent = new MyEntity();
        ent.AddCustomProperty("Title", "Mr");
        ent.AddCustomProperty("FirstName", "John");
        ent.AddCustomProperty("Name", "Smith");

        this.DataContext = ent;

    }

MainPage Xaml:-

        <TextBox Height="23" Name="TextBox1" Text="{Binding [Title], Mode=TwoWay}" />
        <TextBox Height="23" Name="TextBox2" Text="{Binding [FirstName], Mode=TwoWay}" />
        <TextBox Height="23" Name="TextBox3" Text="{Binding [Name], Mode=TwoWay}" />

对您的问题而言，重要的是您的代码涉及将属性值分配到字典中。原来你的代码暴露了Dictionary，所有的分配工作都通过框架组件代码。在此版本中，MyEntity 有一个字符串索引器，其中直接分配自定义属性并将Dictionary 设为私有。

请注意，INotifyPropertyChanged 的实现对于回答您的具体问题并不是绝对必要的，但我怀疑您会需要它。例如，如果您将新值重新分配给自定义属性，您会希望 UI 得到通知。

Answer 2

除了INotifyPropertyChanged interface 之外，集合还需要实现INotifyCollectionChanged interface 以支持数据绑定。 ObservableCollection class 为类似列表的集合实现它们，但我相信 .NET Framework 中没有类似字典的集合可以做到这一点。您可能必须自己实现它。