Question

我在Windows Phone 8项目上有以下ListPickers：

<toolkit:ListPicker Name="Continentes" ExpansionMode="ExpansionAllowed" Grid.Row="1" Width="220" Margin="20,20,261,14" Background="White" Foreground="Black" SelectionChanged="Continentes_SelectionChanged" Canvas.ZIndex="10">
</toolkit:ListPicker>

<Image Source="/Assets/Images/arrow@2x.png" Width="16.5" Height="10.5" Margin="187,49,276,567" Grid.Row="1" Canvas.ZIndex="10" />

<toolkit:ListPicker Name="Paises"  Grid.Row="1" Width="220" Margin="249,20,20,20" Background="White" Foreground="Black" Canvas.ZIndex="10">
</toolkit:ListPicker>

第一个ListPicker将被一个字符串列表填充，然后显示一个大陆列表：

Europe,
Asia,
India...

当我选择其中一个大陆时，第二个选择器将使用以下函数填充包含国家/地区的字符串列表，该函数将使用SelectionChanged事件处理程序在第一个选择器上激活：

private void Continentes_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    var selectedItem = (sender as ListPicker).SelectedItem;
    int selindex = Continentes.SelectedIndex;
    List<string> listaDePaises = new List<string>();

    if (selindex != -1)
    {
        if ((string)selectedItem == "Europa")
        {
            Paises.Items.Clear();
            listaDePaises = countrys.getPaisesByName("Europa");
            Paises.ItemsSource = listaDePaises;
        }

        if ((string)selectedItem == "Asia")
        {
            Paises.Items.Clear();
            listaDePaises = countrys.getPaisesByName("Asia");
            Paises.ItemsSource = listaDePaises;
        }
    }
}

第一次执行continente selection时，第二个选择器会被填充，但第二次尝试时，我在Items.Clear()方法上得到了以下异常。

An exception of type 'System.InvalidOperationException' occurred in System.Windows.ni.dll but was not handled in user code

Additional information: Operation not supported on read-only collection.

对我做错了什么的想法？

Answer 1

当listpicker的ItemsSource与dataSource绑定时，Items已经是只读集合。你可以这样做：Paises.ItemsSource = null;但不是：Items.Clear（）。我希望它可以帮到你。

ListPicker Items.Clear

1 个答案: