INotifyPropertyChanged 和线程

Question

我有一个实现INotifyPropertyChanged 的基类：

protected void OnNotifyChanged(string pName)
{
    if (PropertyChanged != null)
    {
        PropertyChanged(this, new PropertyChangedEventArgs(pName));
    }
}

public event PropertyChangedEventHandler PropertyChanged;

我有一个带有属性Latitude 的派生类，如下所示：

private double latitude;

public double Latitude
{
    get { return latitude; }
    set { latitude = value; OnNotifyChanged("Latitude"); }
}

我的派生类也有一个方法Fly 可以操作Latitude。

我还有一个表单，其 TextBox 绑定到我的派生类的 Latitude：

txtLat.DataBindings.Clear();    
txtLat.DataBindings.Add("Text", bindSrc, "Latitude");

一个线程用于启动Fly，如下所示：

Thread tFly = new Thread(f.Fly);
tFly.IsBackground = true;
tFly.Start();

当Latitude改变时，抛出异常：

DataBinding cannot find a row in the list that is suitable for all bindings.

Answer 1

这似乎是线程关联的一个奇怪问题。最终，代码试图从非 UI 线程进行更新 - 我不清楚为什么它不只是显示跨线程异常 - 我想知道这是否实际上是一个包罗万象的异常处理程序。如果我删除 BindingSource（并直接绑定到对象，这是有效的），您确实会得到一个跨线程异常（这是我所期望的）。

就个人而言，我倾向于手动处理此问题，即使用对 UI 线程执行 Invoke 并手动更新 Text 的方法订阅事件。但是，我只是在检查一些以前的跨线程绑定代码是否有帮助......

---

这是一个使用Invoke的例子：

using System;
using System.ComponentModel;
using System.Threading;
using System.Windows.Forms;

class FlightUav : INotifyPropertyChanged
{
    protected void OnNotifyChanged(string pName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(pName));
    }
    public event PropertyChangedEventHandler PropertyChanged;
    private double _latitude;
    public double Latitude
    {
        get { return _latitude; }
        set { _latitude = value; OnNotifyChanged("Latitude"); }
    }
    public void Fly()
    {
        for (int i = 0; i < 100; i++)
        {
            Latitude++;
            Thread.Sleep(10);
        }
    }
    [STAThread]
    static void Main()
    {
        using (Form form = new Form())
        {
            FlightUav currentlyControlledFlightUav = new FlightUav();

            currentlyControlledFlightUav.PropertyChanged += delegate
            { // this should be in a *regular* method so that you can -= it when changing bindings...
                form.Invoke((MethodInvoker)delegate
                {
                    form.Text = currentlyControlledFlightUav.Latitude.ToString();
                });
            };


            using (Button btn = new Button())
            {
                btn.Text = "Fly";
                btn.Click += delegate
                {
                    Thread tFly = new Thread(currentlyControlledFlightUav.Fly);
                    tFly.IsBackground = true;
                    tFly.Start();
                };
                form.Controls.Add(btn);
                Application.Run(form);
            }
        }
    }


}

---

这是一个使用我的一些旧线程代码的（修改）版本的示例：

using System;
using System.ComponentModel;
using System.Threading;
using System.Windows.Forms;

class FlightUav : INotifyPropertyChanged
{
    protected void OnNotifyChanged(string pName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(pName));
    }
    public event PropertyChangedEventHandler PropertyChanged;
    private double _latitude;
    public double Latitude
    {
        get { return _latitude; }
        set { _latitude = value; OnNotifyChanged("Latitude"); }
    }
    public void Fly()
    {
        for (int i = 0; i < 100; i++)
        {
            Latitude++;
            Thread.Sleep(10);
        }
    }
    [STAThread]
    static void Main()
    {
        using (Form form = new Form())
        {
            FlightUav currentlyControlledFlightUav = new FlightUav();
            BindingSource bindSrc = new BindingSource();
            var list = new ThreadedBindingList<FlightUav>();
            list.Add(currentlyControlledFlightUav);
            bindSrc.DataSource = list;

            form.DataBindings.Clear();
            form.DataBindings.Add("Text", list, "Latitude");

            using (Button btn = new Button())
            {
                btn.Text = "Fly";
                btn.Click += delegate
                {
                    Thread tFly = new Thread(currentlyControlledFlightUav.Fly);
                    tFly.IsBackground = true;
                    tFly.Start();
                };
                form.Controls.Add(btn);
                Application.Run(form);
            }
        }
    }


}
public class ThreadedBindingList<T> : BindingList<T>
{
    private readonly SynchronizationContext ctx;
    public ThreadedBindingList()
    {
        ctx = SynchronizationContext.Current;
    }
    protected override void OnAddingNew(AddingNewEventArgs e)
    {
        SynchronizationContext ctx = SynchronizationContext.Current;
        if (ctx == null)
        {
            BaseAddingNew(e);
        }
        else
        {
            ctx.Send(delegate
            {
                BaseAddingNew(e);
            }, null);
        }
    }
    void BaseAddingNew(AddingNewEventArgs e)
    {
        base.OnAddingNew(e);
    }
    protected override void OnListChanged(ListChangedEventArgs e)
    {
        if (ctx == null)
        {
            BaseListChanged(e);
        }
        else
        {
            ctx.Send(delegate
            {
                BaseListChanged(e);
            }, null);
        }
    }
    void BaseListChanged(ListChangedEventArgs e)
    {
        base.OnListChanged(e);
    }
}