绑定ListPicker.SelectedIndex问题

Question

我正在尝试在Windows Phone 7 UserControl中对ListPicker的SelectedIndex属性进行双向绑定.

当我设置DataContext时,它引发以下异常: SelectedIndex must always be set to a valid value.

这是XAML代码

<Grid x:Name="LayoutRoot">
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"/>
        <RowDefinition Height="Auto"/>
    </Grid.RowDefinitions>

    <toolkit:ListPicker
        Grid.Row="0"
        x:Name="List1"
        SelectionChanged="Picker_SelectionChanged"
        SelectedIndex="{Binding PickerSelectedIndex, Mode=TwoWay}"
        ItemTemplate="{StaticResource PickerTemplate}"
        ItemsSource="{Binding MyList}"/>
</Grid>

和DataContext背后的代码

    private ObservableCollection<MyClass> myList = null;
    public ObservableCollection<MyClass> MyList
    {
        get { return this.myList; }
        set
        {
            if (value != this.myList)
            {
                this.myList= value;
                NotifyPropertyChanged("MyList");

                this.PickerSelectedIndex = 0;
            }
        }
    }

    private int pickerSelectedIndex = 0;
    public int PickerSelectedIndex
    {
        get
        {
            return this.pickerSelectedIndex;
        }
        set
        {
            this.pickerSelectedIndex= value;
        }
    }

在PickerSelectedIndex.get我的断点中可以看到它正确返回(0).我确信问题是SelectedIndex="{Binding PickerSelectedIndex, Mode=TwoWay}"因为删除此行可以解决问题,我可以看到ListPicker正确加载了来自MyList的数据.

我看不出问题出在哪里......

Answer 1

移动SelectedIndex后ItemsSource解决了问题.

这是工作片段

<toolkit:ListPicker
    Grid.Row="0"
    x:Name="List1"
    SelectionChanged="Picker_SelectionChanged"
    ItemTemplate="{StaticResource PickerTemplate}"
    ItemsSource="{Binding MyList}"
    SelectedIndex="{Binding PickerSelectedIndex, Mode=TwoWay}"/>

有人对此有解释吗？