我想我已经弄清楚了。我不明白如何将变更通知从控件发送到绑定的数据源。

是的，调用OnValidating（）是错误的方式。

从我拼接在一起，控件可以通过两种方式通知数据源属性已更改。

一种方法是控制实现INotifyPropertyChanged。我从来没有从控制端这样做过，我只想到绑定的数据源端必须实现它。

当我在用户控件上实现了INotifyPropertyChanged，并在适当的时候调用了PropertyChanged事件，它的工作正常。

第二种方法是让控件为每个属性引发一个特定的改变事件。事件必须遵循命名约定：< propertyname>已更改

对于我的例子，它将是

公共事件EventHandler ControlPropertyChanged

如果我的财产被称为Foo，那将是 FooChanged 。

我未能注意到MSDN 文档，其中说明如下：

要更改通知发生在
绑定客户端和
数据源之间的绑定，绑定类型应该
或者：

实现INotifyPropertyChanged
接口（首选）。

为绑定类型的每个
属性提供更改事件。

第二种方式是所有现有WinForms控件的工作原理，所以这就是我现在所做的工作。我在我的数据源上使用INotifyPropertyChanged，但是在我的控件上提出了更改的事件。这似乎是传统的方式。

I have a simple usercontrol (WinForms) with some public properties. When I use this control, I want to databind to those properties with the DataSourceUpdateMode set to OnPropertyChanged. The datasource is a class which implements INotifyPropertyChanged.

I'm aware of the need to create bindings against the properties and I'm doing that.

I assumed that my usercontrol would have to implement an interface, or the properties would need to be decorated with some attribute, or something along those lines.But my research has come up blank.

How should this be accomplished? At the moment I'm doing it by calling OnValidating() in my usercontrol whenever a property changes, but that doesn't seem right.

I can get validation to happen if I set the CausesValidation to true on the usercontrol, but that's not very useful to me. I need to validate each child property as it changes.

Note this is a WinForms situation.

EDIT: Evidently I have no talent for explanation so hopefully this will clarify what I'm doing. This is an abbreviated example:

// I have a user control
public class MyControl : UserControl
{
    // I'm binding to this property
    public string ControlProperty { get; set; }

    public void DoSomething()
    {
        // when the property value changes, the change should immediately be applied 
        // to the bound datasource
        ControlProperty = "new value";

        // This is how I make it work, but it seems wrong
        OnValidating();         
    }
}

// the class being bound to the usercontrol
public class MyDataSource : INotifyPropertyChanged
{
    private string sourceProperty;
    public string SourceProperty
    {
        get { return sourceProperty; }
        set
        {
            if (value != sourceProperty)
            {
                sourceProperty = value;
                NotifyPropertyChanged("SourceProperty");
            }
        }
    }

    // boilerplate stuff
    public event PropertyChangedEventHandler PropertyChanged;
    protected void NotifyPropertyChanged(string info)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(info));
    }
}

public class MyForm : Form
{
    private MyControl myControl;
    public MyForm()
    {
        // create the datasource 
        var dataSource = new MyDataSource() { SourceProperty = "test" };

        // bind a property of the datasource to a property of the usercontrol
        myControl.DataBindings.Add("ControlProperty", dataSource, "SourceProperty",
            false, DataSourceUpdateMode.OnPropertyChanged); // note the update mode
    }
}

(I have tried this using a BindingSource, but the result was the same.)

Now what I want to happen is that when the value of MyControl.ControlProperty changes, the change is immediately propagated to the datasource (the MyDataSource instance). To achieve this I call OnValidating() in the usercontrol after changing the property. If I don't do that, I have to wait until validation gets triggered by a focus change, which is the equivalent of the "OnValidation" update mode, rather than the desired "OnPropertyUpdate" validation mode. I just don't feel like calling OnValidating() after altering a property value is the right thing to do, even if it (kind of) works.

Am I right in assuming the calling OnValidating() is not the right way to do this? If so, how do I notify the datasource of the ControlProperty change?

I think I've got this figured out. I didn't understand how change notifications were sent from control to bound datasource.

Yes, calling OnValidating() is the wrong way.

From what I've pieced together, there are two ways a control can notify the datasource that a property has changed.

One way is for the control to implement INotifyPropertyChanged. I had never done this from the control side before, and I thought only the datasource side of the binding had to implement it.

When I implemented INotifyPropertyChanged on my user control, and raised the PropertyChanged event at the appropriate time, it worked.

The second way is for the control to raise a specific change event for each property. The event must follow the naming convention: <propertyname>Changed

e.g. for my example it would be

public event EventHandler ControlPropertyChanged

If my property was called Foo, it would be FooChanged.

I failed to notice the relavent part of the MSDN documentation, where it says:

For change notification to occur in a binding between a bound client and a data source, your bound type should either:

Implement the INotifyPropertyChanged interface (preferred).

Provide a change event for each property of the bound type.

This second way is how all existing WinForms controls work, so this is how I'm doing it now. I use INotifyPropertyChanged on my datasource, but I raise the Changed events on my control. This seems to be the conventional way.