DependencyProperty依赖项和PropertyCallbacks

本文的核心问题是,在为其中一个dp设置属性回调时,是否可以期望设置所有dp。我问这个是因为这不是我看到的行为。

<!-- Days of the Week -->
<local:DayOfTheWeekColumn 
    DowIndex="0" 
    ActivityCollection="{Binding Source={StaticResource spy}, Path=DataContext}"
    ....                    
/>

在DayOfWeekColumn类中,DPs的声明如下:

public static readonly DependencyProperty DowIndexProperty = DependencyProperty.RegisterAttached(
        "DowIndex", typeof(string), typeof(DayOfTheWeekColumn), 
        new PropertyMetadata(OnDowIndexSet), IsIndexValid);

    public static readonly DependencyProperty ActivityCollectionProperty = DependencyProperty.RegisterAttached(
        "ActivityCollection", typeof(IActivityCollectionViewModelBase), typeof(DayOfTheWeekColumn), 
        new PropertyMetadata(OnActivityCollectionSet));

当OnDowIndexSet回调执行时,ActivityCollectionProperty仍为null,但当OnActivityCollectionSet回调执行时,将对DowIndexProperty进行赋值。我需要两个属性来完成这个用例。以下是OnActivityCollectionSet:

    private static void OnActivityCollectionSet(DependencyObject target, DependencyPropertyChangedEventArgs e) {
        var context = (IActivityCollectionViewModelBase) e.NewValue;
        var col = (DayOfTheWeekColumn) target;
        var index = Convert.ToInt32(col.DowIndex);
        _setHeader(col, context, index);
    }

现在可以了,但对我来说很脆弱,因为我不知道在回调执行时设置这两个属性的时间。为什么两个属性都可以用于OnActivityCollectionSet而不能用于OnDowIndexSet?

贝里尔