wcf – Silverlight Combobox数据绑定竞争条件

在设置SELEctedItem之后设置Itemsource时存在问题.当发生这种情况时,Combobx将其视为选择的完全重置并清除SELEctedItem / SELEctedIndex.你可以在System.Windows.Controls.Primitives.SELEctor(ComboBox的基类)中看到这个：

protected override void OnItemsChanged(NotifyCollectionChangedEventArgs E)
{
    base.onItemsChanged(E);
    int SELEctedIndex = this.SELEctedIndex;
    bool flag = this.IsInit && this._initializingData.IsIndexSet;
    switch (e.Action)
    {
        case NotifyCollectionChangedAction.Add:
            if (!this.AddedWithSELEctionSet(e.NewStarTingIndex,e.NewStarTingIndex + e.NewItems.Count))
            {
                if ((e.NewStarTingIndex <= SELEctedIndeX) && !flag)
                {
                    this._processingSELEctionPropertyChange = true;
                    this.SELEctedIndex += e.NewItems.Count;
                    this._processingSELEctionPropertyChange = false;
                }
                if (e.NewStarTingIndex > this._focusedIndeX)
                {
                    return;
                }
                this.SetFocusedItem(this._focusedIndex + e.NewItems.Count,falsE);
            }
            return;

        case NotifyCollectionChangedAction.Remove:
            if (((e.oldStarTingIndex > SELEctedIndeX) || (SELEctedIndex >= (e.oldStarTingIndex + e.oldItems.Count))) && (e.oldStarTingIndex < SELEctedIndeX))
            {
                this._processingSELEctionPropertyChange = true;
                this.SELEctedIndex -= e.oldItems.Count;
                this._processingSELEctionPropertyChange = false;
            }
            if ((e.oldStarTingIndex <= this._focusedIndeX) && (this._focusedIndex < (e.oldStarTingIndex + e.oldItems.Count)))
            {
                this.SetFocusedItem(-1,falsE);
                return;
            }
            if (e.oldStarTingIndex < SELEctedIndeX)
            {
                this.SetFocusedItem(this._focusedIndex - e.oldItems.Count,falsE);
            }
            return;

        case NotifyCollectionChangedAction.replace:
            if (!this.AddedWithSELEctionSet(e.NewStarTingIndex,e.NewStarTingIndex + e.NewItems.Count))
            {
                if ((e.oldStarTingIndex <= SELEctedIndeX) && (SELEctedIndex < (e.oldStarTingIndex + e.oldItems.Count)))
                {
                    this.SELEctedIndex = -1;
                }
                if ((e.oldStarTingIndex > this._focusedIndeX) || (this._focusedIndex >= (e.oldStarTingIndex + e.oldItems.Count)))
                {
                    return;
                }
                this.SetFocusedItem(-1,falsE);
            }
            return;

        case NotifyCollectionChangedAction.Reset:
            if (!this.AddedWithSELEctionSet(0,base.Items.Count) && !flag)
            {
                this.SELEctedIndex = -1;
                this.SetFocusedItem(-1,falsE);
            }
            return;
    }
    throw new InvalidoperationException();
}

注意最后一种情况 – 重置…当你加载一个新的Itemsource时,你最终会在这里被任何SELEctedItem / SELEctedIndex吹走？！？！

那么解决方案最终非常简单.我只是将错误的ComboBox子类化,并为此方法提供和覆盖如下.虽然我确实需要添加：

public class FixedComboBox : ComboBox
{
    public FixedComboBox()
        : base()
    {
        // This is here to sync the dep properties (OnSELEctedItemChanged is private is the base class - thanks M$)
        base.SELEctionChanged += (s,E) => { FixedSELEctedItem = SELEctedItem; };
    }

    // need to add a safe dependency property here to bind to - this will store off the "requested SELEctedItem" 
    // this whole this is a kludgy wrapper because the OnSELEctedItemChanged is private in the base class
    public readonly static DependencyProperty FixedSELEctedItemProperty = DependencyProperty.Register("FixedSELEctedItem",typeof(object),typeof(FixedComboBox),new PropertyMetadata(null,new PropertyChangedCallBACk(FixedSELEctedItemPropertyChanged)));
    private static void FixedSELEctedItemPropertyChanged(DependencyObject obj,DependencyPropertyChangedEventArgs E)
    {
        FixedComboBox fcb = obj as FixedComboBox;
        fcb.mLastSELEction = e.NewValue;
        fcb.SELEctedItem = e.NewValue;
    }
    public object FixedSELEctedItem 
    {
        get { return GetValue(FixedSELEctedItemProperty); }
        set { SETVALue(FixedSELEctedItemProperty,value);}
    }
    protected override void OnItemsChanged(System.Collections.Specialized.NotifyCollectionChangedEventArgs E)
    {
        base.onItemsChanged(E);
        if (-1 == SELEctedIndeX)
        {
            // if after the base class is called,there is no SELEction,try
            if (null != mLastSELEction && Items.Contains(mLastSELEction))
                SELEctedItem = mLastSELEction;
        }
    }

    protected object mLastSELEction = null;
}

所有这一切都是(a)保存旧的SELEctedItem然后(b)检查是否在ItemsChanged之后,如果我们没有做出选择并且旧的SELEctedItem存在于新列表中……那么……选择它！