Windows 窗体数据绑定和属性路径：如何处理可空性？

Question

我正在尝试在 Windows 窗体项目中使用MVVM 模式实现master/detail 场景（我知道我很生气）。考虑以下视图模型：

public class MasterViewModel
{
    public BindingList<DetailViewModel> Details { get; set; }

    public DetailViewModel SelectedDetail
    {
        get
        {
            //
        }
        set
        {
            // raises SelectedDetailChanged
        }
    }
}

public class DetailViewModel
{
    public string SubProperty
    {
        get
        {
            // ...
        }
        set
        {
            // ... raises SubPropertyChanged
        }
    }
}

我正在尝试使用以下代码（以及 Windows 窗体数据绑定支持的属性路径）将 DetailViewModel 的 SubProperty 绑定到 TextBox：

            MasterViewModel masterViewModel;
            TextBox textBox;
            // ...

            Binding binding = new Binding("Text", masterViewModel, "SelectedDetail.SubProperty");
            binding.FormattingEnabled = true;
            binding.DataSourceUpdateMode = DataSourceUpdateMode.OnPropertyChanged;
            binding.ControlUpdateMode = ControlUpdateMode.OnPropertyChanged;

            textBox.DataBindings.Add(binding);

它完美地工作（就像 WPF 一样！！！）...直到 SelectedDetail 为空（对于我的逻辑，SelectedDetail null 意味着在主视图中没有选择任何内容）。如果 SelectedDetail 为 null，我得到一个 ArgumentNullException（参数名称：组件）。

有没有办法处理“父”属性的可空性（在导航路径内）？

这里是异常堆栈跟踪：

   in System.ComponentModel.ReflectPropertyDescriptor.AddValueChanged(Object component, EventHandler handler)
   in System.Windows.Forms.BindToObject.CheckBinding()
   in System.Windows.Forms.BindToObject.SetBindingManagerBase(BindingManagerBase lManager)
   in System.Windows.Forms.Binding.SetListManager(BindingManagerBase bindingManagerBase)
   in System.Windows.Forms.ListManagerBindingsCollection.AddCore(Binding dataBinding)
   in System.Windows.Forms.BindingsCollection.Add(Binding binding)
   in System.Windows.Forms.BindingContext.UpdateBinding(BindingContext newBindingContext, Binding binding)
   in System.Windows.Forms.Control.UpdateBindings()
   in System.Windows.Forms.Control.OnBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnParentBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnParentBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnParentBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnParentBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnParentBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.set_BindingContextInternal(BindingContext value)
   in System.Windows.Forms.ContainerControl.set_BindingContext(BindingContext value)
   in System.Windows.Forms.ContainerControl.get_BindingContext()
   in System.Windows.Forms.Control.get_BindingContextInternal()
   in System.Windows.Forms.ContainerControl.get_BindingContext()
   in System.Windows.Forms.Control.get_BindingContextInternal()
   in System.Windows.Forms.ContainerControl.get_BindingContext()
   in System.Windows.Forms.Control.get_BindingContextInternal()
   in System.Windows.Forms.ContainerControl.get_BindingContext()
   in System.Windows.Forms.Control.get_BindingContextInternal()
   in System.Windows.Forms.Control.get_BindingContext()
   in System.Windows.Forms.Control.get_BindingContextInternal()
   in System.Windows.Forms.Control.get_BindingContext()
   in System.Windows.Forms.Control.UpdateBindings()
   in System.Windows.Forms.Control.OnBindingContextChanged(EventArgs e)
   in System.Windows.Forms.DataGridView.OnBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnParentBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnParentBindingContextChanged(EventArgs e)
   in System.Windows.Forms.Control.OnBindingContextChanged(EventArgs e)
   in System.Windows.Forms.ContainerControl.OnCreateControl()
   in System.Windows.Forms.UserControl.OnCreateControl()
   in System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
   in System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
   in System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
   in System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
   in System.Windows.Forms.Control.CreateControl()
   in System.Windows.Forms.Control.WmShowWindow(Message& m)
   in System.Windows.Forms.Control.WndProc(Message& m)
   in System.Windows.Forms.ScrollableControl.WndProc(Message& m)
   in System.Windows.Forms.ContainerControl.WndProc(Message& m)
   in System.Windows.Forms.Form.WmShowWindow(Message& m)
   in System.Windows.Forms.Form.WndProc(Message& m)
...
   in System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   in System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   in System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

Answer 1

您需要BindingSource 来提供一个间接层。

bindingSource1 = new BindingSource(components);
bindingSource1.DataMember = "Details";
bindingSource1.DataSource = typeof(MasterViewModel);

Binding binding = new Binding("Text", bindingSource1, "SubProperty");
binding.FormattingEnabled = true;
binding.DataSourceUpdateMode = DataSourceUpdateMode.OnPropertyChanged;
binding.ControlUpdateMode = ControlUpdateMode.OnPropertyChanged;

textBox.DataBindings.Add(binding);

更详细的例子：BindingSource and BindingNavigator in C# 2.0

Answer 2

您可能想这样尝试：

 Binding binding = 
    new Binding("Text", masterViewModel.SelectedDetail, "SubProperty");