IList作为依赖项属性，setter似乎不起作用

Question

我有以下来自ComboBox自定义用户控件：

public class EnumSourceComboBox : ComboBox
{
    public static readonly DependencyProperty ExcludedItemsProperty =
        DependencyProperty.Register(
            "ExcludedItems", 
            typeof(IList), 
            typeof(EnumSourceComboBox), 
            new PropertyMetadata(
                new List<object>()));

    public EnumSourceComboBox()
    {
        this.ExcludedItems = new List<object>();
    }

    public IList ExcludedItems
    {
        get
        {
            return (IList)this.GetValue(EnumSourceComboBox.ExcludedItemsProperty);
        }

        set
        {
            this.SetValue(EnumSourceComboBox.ExcludedItemsProperty, value);
        }
    }
}

我在XAML使用它的方式如下：

        <controls:EnumSourceComboBox>
            <controls:EnumSourceComboBox.ExcludedItems>
                <employeeMasterData:TaxAtSourceCategory>FixedAmount</employeeMasterData:TaxAtSourceCategory>
                <employeeMasterData:TaxAtSourceCategory>FixedPercentage</employeeMasterData:TaxAtSourceCategory>
            </controls:EnumSourceComboBox.ExcludedItems>
        </controls:EnumSourceComboBox>

这样可以构建良好，并且没有XAML解析异常或类似的东西。 但是， ExcludedItems始终具有count == 0 ，因此XAML中定义的两个项目不会添加到列表中。

如何定义依赖项属性以支持此行为？

更新 ：这是TaxAtSourceCategory枚举：

public enum TaxAtSourceCategory
{
    /// <summary>
    /// The none.
    /// </summary>
    None, 

    /// <summary>
    /// The fixed amount.
    /// </summary>
    FixedAmount, 

    /// <summary>
    /// The fixed percentage.
    /// </summary>
    FixedPercentage, 

    // Has some more values, but I don't think that matters
}

Answer 1

@cguedel，

我尝试了您的DependencyProperty代码，它运行正常。 我在属性的XAML内容中添加了两个字符串，而不是在TaxAtSourceCategory实例中添加了两个字符串。在窗口的Loaded事件中，我对列表2进行了计数。

因此，也许您与TaxAtSourceCategory类有关。 也许您可以显示TaxAtSourceCategory代码，检查构造函数调用...

问候

Answer 2

在以下代码中，有一个EnumSourceCombobox，用于跟踪集合中的更改。
都跟踪：
-集合更改（集合被另一个替换）
-并更改集合（添加/删除/清除）

public class EnumSourceComboBox : ComboBox
{
    private ObservableCollection<TaxAtSourceCategory> previousCollection;

    public static readonly DependencyProperty ExcludedItemsProperty =
        DependencyProperty.Register(
            "ExcludedItems",
            typeof(ObservableCollection<TaxAtSourceCategory>),
            typeof(EnumSourceComboBox),
            new PropertyMetadata(null));
    public ObservableCollection<TaxAtSourceCategory> ExcludedItems
    {
        get
        {
            return (ObservableCollection<TaxAtSourceCategory>)this.GetValue(EnumSourceComboBox.ExcludedItemsProperty);
        }
        set
        {
            this.SetValue(EnumSourceComboBox.ExcludedItemsProperty, value);
        }
    }
    public EnumSourceComboBox()
    {
        DependencyPropertyDescriptor dpd = DependencyPropertyDescriptor.FromProperty(EnumSourceComboBox.ExcludedItemsProperty, typeof(EnumSourceComboBox));
        dpd.AddValueChanged(this, (o, e) =>
        {
            if (previousCollection != null)
                previousCollection.CollectionChanged -= ExcludedItemsChanged;
            previousCollection = ExcludedItems;
            if (previousCollection != null)
                previousCollection.CollectionChanged += ExcludedItemsChanged;
        });
        this.ExcludedItems = new ObservableCollection<TaxAtSourceCategory>();
    }
    void ExcludedItemsChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        // Take into account change in the excluded items more seriously !
        MessageBox.Show("CollectionChanged to count " + ExcludedItems.Count);
    }
}

这是解决方案的链接： http : //1drv.ms/1P8cMVc

最佳使用