Windows Forms Data Binding

Overview

One of the most powerful aspects of .NET and Windows Forms is data binding. Historically, data binding was used to bind views to data stored in databases. Some database management systems, such as Microsoft Access, have provided GUI APIs to help developers quickly bind to data. Each DBMS normally had its on associated API for data binding purposes. Some even had no associated API, which forced developers to provide the implementation from scratch. Binding to other types of data structures, such as arrays, were out of the question. .NET, however, solves all these problems and more. With .NET, a client can bind to almost any data structure, including arrays, collections, data rows, and data views.

Data Binding Concepts

For .NET data binding to be possible, there must be providers of data and consumers of data. A provider of data is an object or component that exposes its data to the outside. A consumer is an object or component that uses the data exposes by a provider with the intention to display or modify that data. With .NET data binding, the minimum requirement to support list-based data binding is for the provider to implement the IList interface. The IList interface represents an index-based collection.

Data Providers

The following objects implement the IList interface; so they are, inherently, data providers.

Arrays

An array is simply a collection  of objects that can be accessed by a numeric index. Arrays can be either single-dimensional or multi-dimensional.

DataSet

The DataSet is a .NET representation of a database. It does not, however, need to actually be connected to a real database. As a matter of fact, it acts as a "disconnected" data source, with the ability to track changes and merge new data. When binding to a DataSet, the consumer is responsible for asking for the particular DataTable to bind to. In some cases, the consumer would really be binding to the DataSet's default DataViewManager.

DataTable

A DataTable typically represents a table in a database. Though, it may also be used to represent the structure of an XML element, or the parent of a collection. A DataTable contains a DataColumn collection and a DataRow collection. Complex controls, such as the .NET DataGrid, can be bound to a DataTable with ease. Note that when you bind to a DataTable, you really bind to the table's default DataView.

DataView

A DataView is simply a customized view of the data in a DataTable. For instance, it may contain all rows sorted by a particular column, or all rows that match a certain expression. When data binding to a DataView, all controls involved in the binding process will receive a snapshot of the data at that particular moment. Whenever the underlying data changes, the bound controls must have some way of knowing how to refresh themselves. This process will be discussed shortly.

DataViewManager

The DataViewManager represents the entire DataSet. Like the DataView, it is a customized snapshot view of the DataSet. The only difference is that it also includes relations.

DataColumn

A DataColumn typically represents, and is analogous to, a column in a database table. Although, it may also represent an XML attribute or an attributeless XML element. You can only simple-bind to a DataColumn. This means that only simple controls, such as a text box, can be bound to a DataColumn.

Other .NET Objects

In actuality, any .NET object may support data binding, but you may not automatically reap all of the benefits provided by the .NET architecture. Also, when binding to these objects, only the public properties (not public fields) can be bound to. Therefore, you must be careful when data binding to data sources exposed by web services. The public properties of any types returned by a web service will be converted to public fields in the web service's client proxy code.

Data Consumers

A consumer is an object or component that uses the data exposed by a provider whose intent is to display or modify that data. In Windows Forms, a consumer is typically a data-bound control. Simple data-bound controls include, but are not limited to, text boxes, labels, check boxes, and radio buttons. These controls can only display one data value provided by a data source. On the other hand, controls such as data grids, list boxes and combo boxes can display a list of values. These controls are therefore referred to as complex data-bound controls.