title: How to have bindable properties of a UserControl which work with OnPropertyChanged
body: <p>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 <strong>OnPropertyChanged</strong>. The datasource is a class which implements INotifyPropertyChanged.</p>
  
  <p>I'm aware of the need to create bindings against the properties and I'm doing that. </p>
  
  <p>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. </p>
  
  <p>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. </p>
  
  <p>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.</p>
  
  <p>Note this is a <strong>WinForms</strong> situation.</p>
  
  <p><strong>EDIT:</strong> Evidently I have no talent for explanation so hopefully this will clarify what I'm doing. This is an abbreviated example:</p>
  
  <pre><code>// 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
      }
  }
  </code></pre>
  
  <p>(I have tried this using a BindingSource, but the result was the same.)</p>
  
  <p>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.</p>
  
  <p>Am I right in assuming the calling OnValidating() is <strong>not</strong> the right way to do this? If so, how do I notify the datasource of the ControlProperty change?</p>