将ComboBox数据与外键数据链接时，从ComboBox中使用了错误的索引

Question

我有一个使用MVVM模式的WPF应用程序。

我有两张表

Customers: CustomerId, CustomerName, CurrencyId

货币:CurrencyId, Description

两个表在主键上使用自动递增，并且在两个CurrencyId列上存在外部关系。

经过一番努力，我可以显示客户列表，单击每个客户，并且我的数据被绑定，但是索引不正确。

Currency表增量从1开始，但ComboBox从0开始，因此基本上对于每个客户，显示的货币描述都是不正确的。

不确定是否需要，但这是我的代码到目前为止。

ViewModel:

    public class TestingViewModel : ViewModelBase
    {
        // Constructor
        public TestingViewModel()
        {
            Customers = GetCustomers();
            Currencies = GetCurrencies();
        }
        private ObservableCollection<Customer> _customers;
        public ObservableCollection<Customer> Customers
        {
            get { return _customers; }
            set
            {
                _customers = value;
                RaisePropertyChanged("Customers");
            }
        }
        private ObservableCollection<Currency> _currencies;
        public ObservableCollection<Currency> Currencies
        {
            get { return _currencies; }
            set
            {
                _currencies = value;
                RaisePropertyChanged("Currencies");
            }
        }
        private ObservableCollection<Customer> GetCustomers()
        {
            var dbContext = new DbDataContext();
            return new ObservableCollection<Customer> dbContext.Customers.ToList());
        }
        private ObservableCollection<Currency> GetCurrencies()
        {
            var dbContext = new DbDataContext();
            return new ObservableCollection<Currency>(dbContext.Currencies.ToList());
        }
    }

视图:

<Grid>
    <ListView x:Name="LstCustomers" Grid.Column="0" Grid.Row="1"  
                      ItemsSource="{Binding Path=Customers, Mode=Oneway}" IsSynchronizedWithCurrentItem="True" Background="White"         
                      ItemContainerStyle="{StaticResource   ListViewItemsStyle}">
                <ListView.ItemTemplate>
                    <DataTemplate >
                        <TextBlock Text="{Binding Path=CustomerName, Mode=OneTime}"/>
                    </DataTemplate>
                </ListView.ItemTemplate>
            </ListView>            

    <TextBox x:Name="TbContactName" Width="300" Height="30" Margin="0,-100,0,0"
                     VerticalAlignment="Center" HorizontalAlignment="Right" 
                    Text="{Binding ElementName=LstCustomers, Path=SelectedItem.ContactName, UpdateSourceTrigger=PropertyChanged}" />
    <ComboBox x:Name="combobox" ItemsSource="{Binding Currencies}" Width="300" Height="40" HorizontalAlignment="Right"
              DisplayMemberPath="Description"
              SelectedValuePath="CurrencyId"         
              SelectedIndex="{Binding ElementName=LstCustomers, Path=SelectedItem.CurrencyId}" />

</Grid>

在我的代码中是否有不正确的东西，或者我如何解决这个问题?

谢谢,

Answer 1

您依赖于组合框中货币的索引与其CurrencyId相同，这是错误的- CurrencyId是它们在数据库中的id，组合框中货币元素的索引取决于它们在组合框中的顺序。

我将在ViewModel中添加SelectedCustomer和SelectedCurrency属性，并从SelectedCustomer属性setter中更新SelectedCurrency。例如:

private Customer _selectedCustomer;
public Customer SelectedCustomer
{
    get { return _selectedCustomer; }
    set
    {
        _selectedCustomer = value;
        RaisePropertyChanged("SelectedCustomer");
        SelectedCurrency = this.Currencies
            .FirstOrDefault(x => x.CurrencyId == SelectedCustomer.CurrencyId);
    }
}
private Currency _selectedCurrency;
public Currency SelectedCurrency
{
    get { return _selectedCurrency; }
    set
    {
        _selectedCurrency = value;
        RaisePropertyChanged("SelectedCurrency");
    }
}

然后，不做SelectedIndex="{Binding ElementName=LstCustomers, Path=SelectedItem.CurrencyId}"，像SelectedItem = {Binding SelectedCurrency}一样绑定它，并对SelectedCustomer做同样的操作。