为什么我的自定义用户控件的依赖属性不能与绑定一起使用？

Question

如果值在调用它的 XAML 中静态定义，我的自定义 UserControl 的依赖属性将正确绑定，如下所示：

ItemTypeIdCode="addresses"

但如果值动态绑定，则不会正确 绑定strong> 本身：

ItemTypeIdCode="{Binding ItemTypeIdCode}"

我必须对自定义 UserControl 执行什么操作，才能使其依赖属性对另一个控件中绑定自身的值做出反应？

这是我的代码：

XAML：

<Window x:Class="TestDepenProp.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:controls="clr-namespace:TestDepenProp.Controls"
    Title="Window1" Height="300" Width="300">
    <StackPanel 
        HorizontalAlignment="Left"
        Margin="10">
        <controls:DropDown 
            ItemTypeIdCode="{Binding ItemTypeIdCode}"  
            SelectedValue="672"
            Width="150"
            Margin="0 0 0 5"/>
        <TextBlock Text="{Binding ItemTypeIdCode}"/>
    </StackPanel>
</Window>

代码隐藏：

using System.Windows;
using System.ComponentModel;

namespace TestDepenProp
{
    public partial class Window1 : Window, INotifyPropertyChanged
    {
        #region ViewModelProperty: ItemTypeIdCode
        private string _itemTypeIdCode;
        public string ItemTypeIdCode
        {
            get
            {
                return _itemTypeIdCode;
            }

            set
            {
                _itemTypeIdCode = value;
                OnPropertyChanged("ItemTypeIdCode");
            }
        }
        #endregion

        public Window1()
        {
            InitializeComponent();
            DataContext = this;

            ItemTypeIdCode = "addresses";
        }
        #region INotifiedProperty Block
        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;

            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }
        #endregion
    }
}

DropDown.xaml：

<UserControl x:Class="TestDepenProp.Controls.DropDown"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <StackPanel>
        <ComboBox SelectedValuePath="Key"
                  DisplayMemberPath="Value"
                  SelectedValue="{Binding SelectedValue}"
                  Margin="0 0 0 10"
                  ItemsSource="{Binding DropDownValues}" />
    </StackPanel>
</UserControl>

DropDown.xaml.cs：

using System.Windows;
using System.Windows.Controls;
using System.ComponentModel;
using System.Collections.ObjectModel;
using System.Collections.Generic;

namespace TestDepenProp.Controls
{
    public partial class DropDown : UserControl, INotifyPropertyChanged
    {

        public static readonly DependencyProperty ItemTypeIdCodeProperty = DependencyProperty.Register("ItemTypeIdCode", typeof(string), typeof(DropDown));

        public string ItemTypeIdCode
        {
            get { return (string)GetValue(ItemTypeIdCodeProperty); }
            set { SetValue(ItemTypeIdCodeProperty, value); }
        }

        #region ViewModelProperty: DropDownValues
        private ObservableCollection<KeyValuePair<string, string>> _dropDownValues = new ObservableCollection<KeyValuePair<string, string>>();
        public ObservableCollection<KeyValuePair<string, string>> DropDownValues
        {
            get
            {
                return _dropDownValues;
            }

            set
            {
                _dropDownValues = value;
                OnPropertyChanged("DropDownValues");
            }
        }
        #endregion

        #region ViewModelProperty: SelectedValue
        private string _selectedValue;
        public string SelectedValue
        {
            get
            {
                return _selectedValue;
            }

            set
            {
                _selectedValue = value;
                OnPropertyChanged("SelectedValue");
            }
        }
        #endregion

        public DropDown()
        {
            InitializeComponent();
            DataContext = this;

            Loaded += new RoutedEventHandler(DropDown_Loaded);
        }

        void DropDown_Loaded(object sender, RoutedEventArgs e)
        {
            GetDropDownValues();
        }

        void GetDropDownValues()
        {
            switch (ItemTypeIdCode)
            {
                case "addresses":
                    DropDownValues.Add(new KeyValuePair<string, string>("111", "762 Main St."));
                    DropDownValues.Add(new KeyValuePair<string, string>("222", "7384 First Ave."));
                    DropDownValues.Add(new KeyValuePair<string, string>("333", "8728 Second St."));
                    break;
                case "customers":
                    DropDownValues.Add(new KeyValuePair<string, string>("672", "Jim Smith"));
                    DropDownValues.Add(new KeyValuePair<string, string>("281", "James Anders"));
                    DropDownValues.Add(new KeyValuePair<string, string>("321", "Angie Wonderson"));
                    DropDownValues.Add(new KeyValuePair<string, string>("221", "Hal Cloud"));
                    DropDownValues.Add(new KeyValuePair<string, string>("123", "Hugh Brandley"));
                    break;
                default:
                    break;
            }
        }


        #region INotifiedProperty Block
        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;

            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }
        #endregion


    }
}

Answer 1

我认为您需要将 PropertyChangedCallback 添加到 ItemTypeIdCodeProperty 依赖项属性中。在此回调中，您将调用 GetDropDownValues()。

Answer 2

我的猜测是组合框不显示任何条目。这确实有点棘手。一个控件在 2 个完全独立的“地址空间”中工作。第一个是它自己的数据，如所有依赖属性。第二个“地址空间”是它从其父级继承的数据上下文。如果没有做任何特别的事情，所有绑定都将在数据上下文上工作。如果您想引用控件的数据，您需要为自己添加显式“引用”：

<UserControl x:Class="TestDepenProp.Controls.DropDown"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Name="self">
<StackPanel>
    <ComboBox SelectedValuePath="Key"
              DisplayMemberPath="Value"
              SelectedValue="{Binding SelectedValue, ElementName=self}"
              Margin="0 0 0 10"
              ItemsSource="{Binding DropDownValues, ElementName=self}" />
</StackPanel>

不需要 OnPropertyChanged，它已经由依赖属性逻辑处理。