相关疑难解决方法(0)

我在Windows Phone 7应用程序中有一个页面,用户可以在其中编辑或删除Transaction对象.Transaction对象是Linq-to-Sql类,它与Account类和Category类有关系.在页面中,我使用ListPicker让用户选择给定事务的帐户和类别,如下所示:

<toolkit:ListPicker Grid.Row="1" FullModeHeader="Choose the Account" FullModeItemTemplate="{StaticResource FullModeItemTemplate}" ExpansionMode="FullScreenOnly" Background="#26000000" Margin="10,0,10,0" Name="Account" SelectedItem="{Binding Account, Mode=TwoWay}" Tap="ListPicker_Tap" />

<toolkit:ListPicker Grid.Row="7" FullModeHeader="Choose the Category" FullModeItemTemplate="{StaticResource FullModeItemTemplate}" ExpansionMode="FullScreenOnly" Background="#26000000" Margin="10,0,10,0" Name="Category" SelectedItem="{Binding Category, Mode=TwoWay}" Tap="ListPicker_Tap" />

ListPicker_Tap事件是针对Windows Phone的WPF Toolkit的Aug/2011版本中的错误的修复,简单地说是:

    private void ListPicker_Tap(object sender, System.Windows.Input.GestureEventArgs e)
    {
        ListPicker lp = (ListPicker)sender; 
        lp.Open();
    }

如果用户编辑事务,一切都很好,但如果用户尝试删除它,我会收到一条错误,指出"SelectedItem必须始终设置为有效值".

如果用户单击TransactionPage.xaml.cs中appbar中的delete按钮,则代码如下:

    private void appBarDelete_Click(object sender, EventArgs e)
    {
        MessageBoxResult result = MessageBox.Show("Are you sure?\n", "Confirm", MessageBoxButton.OKCancel);

        if (result == MessageBoxResult.OK)
        {
            App.ViewModel.DeleteTransaction(transaction);
        }

        NavigationService.GoBack();
    }

我的ViewModel.DeleteTransaction方法:

    public void …