c# - "Two-way binding requires Path or XPath"编辑 wpf 数据网格时

Question

ContractListUserControl.XAML

<DataGrid AutoGenerateColumns="False"
              ItemsSource="{Binding Path=ContractList}"
              SelectedItem="{Binding Path=SelectedContract}">
        <DataGrid.Columns>
            <DataGridTextColumn Binding="{Binding Path=Person.LastName}" Header="Last Name" />
            <DataGridTextColumn Binding="{Binding Path=Person.GivenName}" Header="Given Name" />
            <DataGridTextColumn Binding="{Binding Path=ContractStart, StringFormat=dd/MM/yyyy, Mode=TwoWay}" Header="Contract Start" />
            <DataGridTextColumn Binding="{Binding Path=ContractEnd, StringFormat=dd/MM/yyyy, Mode=TwoWay}" Header="Contract End" />
        </DataGrid.Columns>
</DataGrid>

契约(Contract).cs

public class Contract
{
    public DateTime ContractStart { get; set; }
    public DateTime ContractEnd { get; set; }
    public Person Person { get; set; }
}

Person.cs

public class Person
{
    public string LastName { get; set; }
    public string GivenName { get; set; }
}

ViewModel.cs

public class ContractListViewModel : INotifyPropertyChanged
{
    private ObservableCollection<Contract> _contractList;
    public ObservableCollection<Contract> ContractList
    {
        get { return _contractList; }
        set { SetField(ref _contractList, value, () => ContractList); } // Same as OnPropertyChanged
    }

    private Contract _selectedContract;
    public Contract SelectedContract
    {
        get { return _selectedCrew; }
        set { SetField(ref _selectedCrew, value, () => SelectedCrew); }
    }
}

如果我将数据网格设置为只读，它工作正常，问题是当我直接编辑 LastName 和 GivenName DataGrid 列时，它会崩溃，并抛出带有消息“双向绑定(bind)需要路径或 XPath”的 InvalidOperationException。但是，如果我只编辑 ContractStart 和 ContractEnd，它就可以正常工作。

我搜索了一些帮助，我想我和这个人遇到了同样的情况: DataGrid - "Two-way binding requires Path or XPath."

所以问题是 Person 属性为空，答案说我应该初始化绑定(bind)在 DataContext 中的对象，但没有说明如何去做。

Answer 1

要实现Person属性的初始化可以修改如下

public class Contract
{
    public Contract()
    {
        Person = new Person();
    }

    public string RankName { get; set; }
    public string RankShortName { get; set; }
    public Person Person { get; set; }
}

添加一个构造函数并相应地初始化