C# 绑定到嵌套对象上的字段

Question

我似乎找不到关于如何使用数据绑定将 WinForms 应用程序中的控件绑定到嵌套对象的简单、具体的解释。例如：

class MyObject : INotifyPropertyChanged
{
    private string _Name;
    public string Name 
    { 
        get { return _Name; } 
        set 
        { 
            _Name = value; 
            OnPropertyChanged("Name"); 
        }    
    }

    private MyInner _Inner;
    public MyInner Inner 
    { 
       get { return _Inner; } 
       set 
       { 
           _Inner = value; 
           OnPropertyChanged("Inner"); 
       } 
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

class MyInner : INotifyPropertyChanged
{
    private string _SomeValue;
    public string SomeValue 
    {
        get { return _SomeValue; } 
        set 
        { 
            _SomeValue = value; 
            OnPropertyChanged("SomeValue"); 
        } 
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

现在想象一个只有两个文本框的表单，第一个用于 Name，第二个用于 Inner.SomeValue。我很容易就能绑定到 Name，但 Inner.SomeValue 很不稳定。如果我填充对象然后设置绑定，它会在文本框中显示 Inner.SomeValue 但我无法编辑它。如果我从一个新的对象开始而不初始化 Inner，我似乎无法将数据保留在 Inner.SomeValue 中。

我查遍了 MSDN、StackOverflow，并使用不同的关键字进行了数十次搜索。每个人都想谈论与数据库或 DataGrid 的绑定，并且大多数示例都是用 XAML 编写的。

更新：我已经尝试了马克的完整测试工具并取得了部分成功。如果我点击“全部改变！”按钮，我似乎能够写回到内部对象。但是，从 MyObject.Inner null 开始，它不知道如何创建内部对象。我认为现在，我可以通过确保我的内部引用始终设置为有效对象来解决这个问题。尽管如此，我还是忍不住觉得自己错过了一些东西:)

Answer 1

嗯——一个很好的问题；我已经完成了大量与对象的数据绑定，并且我发誓你所做的应该有效；但它确实很不愿意注意到内部对象的变化。我设法让它工作：

var outer = new BindingSource { DataSource = myObject };
var inner = new BindingSource(outer, "Inner");
txtName.DataBindings.Add("Text", outer, "Name");
txtSomeValue.DataBindings.Add("Text", inner, "SomeValue");

不理想，但它有效。顺便提一句;您可能会发现以下实用程序方法很有用：

public static class EventUtils {
    public static void SafeInvoke(this EventHandler handler, object sender) {
        if(handler != null) handler(sender, EventArgs.Empty);
    }
    public static void SafeInvoke(this PropertyChangedEventHandler handler,
               object sender, string propertyName) {
        if(handler != null) handler(sender,
               new PropertyChangedEventArgs(propertyName));
    }
}

然后您可以拥有：

class MyObject : INotifyPropertyChanged
{
    private string _Name;
    public string Name { get { return _Name; } set {
        _Name = value; PropertyChanged.SafeInvoke(this,"Name"); } }
    private MyInner _Inner;
    public MyInner Inner { get { return _Inner; } set {
        _Inner = value; PropertyChanged.SafeInvoke(this,"Inner"); } }
    public event PropertyChangedEventHandler PropertyChanged;
}

class MyInner : INotifyPropertyChanged
{
    private string _SomeValue;
    public string SomeValue { get { return _SomeValue; } set {
        _SomeValue = value; PropertyChanged.SafeInvoke(this, "SomeValue"); } }
    public event PropertyChangedEventHandler PropertyChanged;
}

并且在讨价还价中，它修复了空异常（竞争条件）的（很小）机会。

---

完整的测试装置，以解决问题（来自评论）：

using System;
using System.ComponentModel;
using System.Windows.Forms;
public static class EventUtils {
    public static void SafeInvoke(this PropertyChangedEventHandler handler, object sender, string propertyName) {
        if(handler != null) handler(sender, new PropertyChangedEventArgs(propertyName));
    }
}
class MyObject : INotifyPropertyChanged
{
    private string _Name;
    public string Name { get { return _Name; } set { _Name = value; PropertyChanged.SafeInvoke(this,"Name"); } }
    private MyInner _Inner;
    public MyInner Inner { get { return _Inner; } set { _Inner = value; PropertyChanged.SafeInvoke(this,"Inner"); } }
    public event PropertyChangedEventHandler PropertyChanged;
}

class MyInner : INotifyPropertyChanged
{
    private string _SomeValue;
    public string SomeValue { get { return _SomeValue; } set { _SomeValue = value; PropertyChanged.SafeInvoke(this, "SomeValue"); } }
    public event PropertyChangedEventHandler PropertyChanged;
}
static class Program
{
    [STAThread]
    public static void Main() {
        var myObject = new MyObject();
        myObject.Name = "old name";
        // optionally start with a default
        //myObject.Inner = new MyInner();
        //myObject.Inner.SomeValue = "old inner value";

        Application.EnableVisualStyles();
        using (Form form = new Form())
        using (TextBox txtName = new TextBox())
        using (TextBox txtSomeValue = new TextBox())
        using (Button btnInit = new Button())
        {
            var outer = new BindingSource { DataSource = myObject };
            var inner = new BindingSource(outer, "Inner");
            txtName.DataBindings.Add("Text", outer, "Name");
            txtSomeValue.DataBindings.Add("Text", inner, "SomeValue");
            btnInit.Text = "all change!";
            btnInit.Click += delegate
            {
                myObject.Name = "new name";
                var newInner = new MyInner();
                newInner.SomeValue = "new inner value";
                myObject.Inner = newInner;
            };
            txtName.Dock = txtSomeValue.Dock = btnInit.Dock = DockStyle.Top;
            form.Controls.AddRange(new Control[] { btnInit, txtSomeValue, txtName });
            Application.Run(form);
        }
    }

}