IList作為依賴項屬性，setter似乎不起作用

Question

我有以下來自ComboBox自定義用戶控件：

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>

這樣可以構建良好，並且沒有XAML解析異常或類似的東西。 但是， ExcludedItems始終具有count == 0 ，因此XAML中定義的兩個項目不會添加到列表中。

如何定義依賴項屬性以支持此行為？

更新 ：這是TaxAtSourceCategory枚舉：

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，

我嘗試了您的DependencyProperty代碼，它運行正常。 我在屬性的XAML內容中添加了兩個字符串，而不是在TaxAtSourceCategory實例中添加了兩個字符串。在窗口的Loaded事件中，我對列表2進行了計數。

因此，也許您與TaxAtSourceCategory類有關。 也許您可以顯示TaxAtSourceCategory代碼，檢查構造函數調用...

問候

Answer 2

在以下代碼中，有一個EnumSourceCombobox，用於跟蹤集合中的更改。
都跟蹤：
-集合更改（集合被另一個替換）
-並更改集合（添加/刪除/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);
    }
}

這是解決方案的鏈接： http : //1drv.ms/1P8cMVc

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