Deep Binding

Introduction

DataBinding is a very powerful tool to push data from objects to the user interface and pull back user data to the object. However, when you have complex objects, Windows Form DataBinding is not so powerful.

In this article, I will demonstrate how we can make a complex databinding between business objects and Windows Forms controls by implementing a few interfaces.

The "Complex Object" Sample

The sample here is a book that has Name, PagesNumber and Author properties. The author has name and BirthDate properties. In the object model, we create a book class that implements book properties and a second class Author. The Author property in the Book class is typed as Author.

Here is the code needed in the Book class:

public class Book : BindableObject
{
public Book()
{
}
public Book(string name,int pagesnumber, Author a)
{
this.Name = name;
this.PagesNumber = pagesnumber;
this.Author = a;
}
private string _Name;
public string Name
{
get{return _Name;}
set{_Name = value;}
}
private int _PagesNumber;
public int PagesNumber
{
get{return _PagesNumber;}
set{_PagesNumber = value;}
}
public Author _Author = new Author();
public Author Author 
{
get{return _Author;}
set{_Author = value;}
}
}

The DataBinding Problem

When we want to create a collection of books and show it to the user in datagrid, we can show only the name and Pagesnumber information. That is because in the MappingName property of the DatagridTextBox, we cannot put Author.Name for example to display the name of the book's author.

The Solution

When binding an object to a Windows Form control, the Framework uses reflection to get bindable properties of the object. However, when an object implements the IcustomTypeDescriptor interface, the framework gets object properties from IcustomTypeDescriptor.GetProperties() method. So the solution is to include all the properties we need to display.

In book example IcustomTypeDescriptor.GetProperties() will return : Name, PagesNumber, Author.Name and Author.BirthDate properties.

Doing this, you can display the Author name of a book in a datagrid just by writing "Author.Name" in the MappingName property of the DatagridTextBox. Also if you have a multicolumn combobox, you can display both Book Name and Author Name.

The Source Code

A class name BindableObject is included in the project. This class implements IcustomTypeDescriptor interface. All business objects created (Book and Author classes) inherit from this class. So no code must be written in business classes.

To get properties of an object, reflection is used. To increase performance, I implemented a cache in which I store objects structure, so reflection is used only one time for each type.

When binding a collection, it must implement the ItypedList interface to call the IcustomTypeDescriptor.GetProperties() method. So the BookCollection class inherits from BindableCollection class included in the project.