C# Databinding: Create object if null

I have a report object (i.e. a business object) which has several dozen fields to populate. Each field by itself has INotifyPropertyChanged implemented. There is an accessor property for the active report called ActiveReport.

What I want to do is be able to Close the current report, without necessarily opening a new one, and be able to automatically create a report object when the user starts to enter data again.

Here is a rough idea of the structure. ActiveReport is the current report. The GUI is able to directly set the fields of the subclass (name/email) through binding. I want a new BusinessObject to be created when name is being set, but ActiveReport is null. One additional caveat, the report object is auto-generated from XSD files, so I'd rather not have to modify those.

class ControlClass {
    public BusinessObject ActiveReport { get; set; }
}

class BusinessObject {
    UserInfo field1 { get; set; }
}

class UserInfo : INotifyPropertyChanged {
    DependencyProperty name;
    DependencyProperty email;
}

I开发者_如何转开发 thought of the following scenarios:

• Accessor property.
  • The binding does not seem to use the accessor.
• Inserting a check into all event handlers.
  • I'd rather not have to resort to this -- this breaks the rationale behind using MVVM.
• Multibinding
  • This would require the use of a converter class and instance, and that seems like overkill.
• Converter

I thought to ask if there were any other good programming models for this in WPF.

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You could create a behavior. in it, you check if (AssociatedObject.DataContext as ReportObject) is null and if it is, clear all your fields / set your datacontext / whatever

---

This should do the trick:

public class ControlClass
{
     public BusinessObject ActiveReport { get; set; }


     private UserInfo _editableUserData 
     public UserInfo EditableUserData
     {
         get { return _editableUserData; }
         set
         { 
             if (_editableUserData != null)
                   _editableUserData.PropertyChanged -= UserDataChanged;

             _editableUserData = value;

             if (_editableUserData != null)
                  _editableUserData.PropertyChanged += UserDataChanged;

             RaisePropertyChanged("EditableUserData");
         }
     }

     private void UserDataChanged(object sender, PropertyChangedEventArgs e)
     {
           if (ActiveReport == null)
                ActiveReport = new BusinessObject(EditableUserData);
     }
}