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Data binding overview (Windows Forms .NET)

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In Windows Forms, you can bind to not just traditional data sources, but also to almost any structure that contains data. You can bind to an array of values that you calculate at run time, read from a file, or derive from the values of other controls.

In addition, you can bind any property of any control to the data source. In traditional data binding, you typically bind the display property—for example, the Text property of a TextBox control—to the data source. With .NET, you also have the option of setting other properties through binding. You might use binding to perform the following tasks:

  • Setting the graphic of an image control.

  • Setting the background color of one or more controls.

  • Setting the size of controls.

Essentially, data binding is an automatic way of setting any run-time accessible property of any control on a form.

ADO.NET lets you create many different data structures to suit the binding needs of your application and the data you're working with. You might want to create your own classes that provide or consume data in Windows Forms. These objects can offer varying levels of functionality and complexity. From basic data binding, to providing design-time support, error checking, change notification, or even support for a structured rollback of the changes made to the data itself.

Consumers of data binding interfaces

The following sections describe two groups of interface objects. The first group of interface is implemented on data sources by data source authors. The data source consumers such as the Windows Forms controls or components implement these interfaces. The second group of interface is designed to use by component authors. Component authors use these interfaces when they're creating a component that supports data binding to be consumed by the Windows Forms data binding engine. You can implement these interfaces within classes associated with your form to enable data binding. Each case presents a class that implements an interface that enables interaction with data. Visual Studio rapid application development (RAD) data design experience tools already take advantage of this functionality.

Interfaces for implementation by data source authors

The Windows Forms controls implement following interfaces:

  • IList interface

    A class that implements the IList interface could be an Array, ArrayList, or CollectionBase. These are indexed lists of items of type Object and the lists must contain homogenous types, because the first item of the index determines the type. IList would be available for binding only at run time.

    Note

    If you want to create a list of business objects for binding with Windows Forms, you should consider using the BindingList<T>. The BindingList is an extensible class that implements the primary interfaces required for two-way Windows Forms data binding.

  • IBindingList interface

    A class that implements the IBindingList interface provides a much higher level of data-binding functionality. This implementation offers you basic sorting capabilities and change notification. Both are useful when the list items change, and when the list itself changes. Change notification is important if you plan to have multiple controls bound to the same data. It helps you to make data changes made in one of the controls to propagate to the other bound controls.

    Note

    Change notification is enabled for the IBindingList interface through the SupportsChangeNotification property which, when true, raises a ListChanged event, indicating the list changed or an item in the list changed.

    The type of change is described by the ListChangedType property of the ListChangedEventArgs parameter. Hence, whenever the data model is updated, any dependent views, such as other controls bound to the same data source, will also be updated. However, objects contained within the list will have to notify the list when they change so that the list can raise the ListChanged event.

    Note

    The BindingList<T> provides a generic implementation of the IBindingList interface.

  • IBindingListView interface

    A class that implements the IBindingListView interface provides all the functionality of an implementation of IBindingList, along with filtering and advanced sorting functionality. This implementation offers string-based filtering, and multi-column sorting with property descriptor-direction pairs.

  • IEditableObject interface

    A class that implements the IEditableObject interface allows an object to control when changes to that object are made permanent. This implementation supports the BeginEdit, EndEdit, and CancelEdit methods, which enable you to roll back changes made to the object. Following is a brief explanation of the functioning of the BeginEdit, EndEdit, and CancelEdit methods and how they work with one another to enable a possible rollback of changes made to the data:

    • The BeginEdit method signals the start of an edit on an object. An object that implements this interface will need to store any updates after the BeginEdit method call in such a way that the updates can be discarded if the CancelEdit method is called. In data binding Windows Forms, you can call BeginEdit multiple times within the scope of a single edit transaction (for example, BeginEdit, BeginEdit, EndEdit). Implementations of IEditableObject should keep track of whether BeginEdit has already been called and ignore subsequent calls to BeginEdit. Because this method can be called multiple times, it's important that subsequent calls to it are nondestructive. Subsequent BeginEdit calls can't destroy the updates that have been made or change the data that was saved on the first BeginEdit call.

    • The EndEdit method pushes any changes since BeginEdit was called into the underlying object, if the object is currently in edit mode.

    • The CancelEdit method discards any changes made to the object.

    For more information about how the BeginEdit, EndEdit, and CancelEdit methods work, see Save data back to the database.

    This transactional notion of data functionality is used by the DataGridView control.

  • ICancelAddNew interface

    A class that implements the ICancelAddNew interface usually implements the IBindingList interface and allows you to roll back an addition made to the data source with the AddNew method. If your data source implements the IBindingList interface, you should also have it implement the ICancelAddNew interface.

  • IDataErrorInfo interface

    A class that implements the IDataErrorInfo interface allows objects to offer custom error information to bound controls:

    • The Error property returns general error message text (for example, "An error has occurred").

    • The Item[] property returns a string with the specific error message from the column (for example, "The value in the State column is invalid").

  • IEnumerable interface

    A class that implements the IEnumerable interface is typically consumed by ASP.NET. Windows Forms support for this interface is only available through the BindingSource component.

    Note

    The BindingSource component copies all IEnumerable items into a separate list for binding purposes.

  • ITypedList interface

    A collections class that implements the ITypedList interface provides the feature to control the order and the set of properties exposed to the bound control.

    Note

    When you implement the GetItemProperties method, and the PropertyDescriptor array is not null, the last entry in the array will be the property descriptor that describes the list property that is another list of items.

  • ICustomTypeDescriptor interface

    A class that implements the ICustomTypeDescriptor interface provides dynamic information about itself. This interface is similar to ITypedList but is used for objects rather than lists. This interface is used by DataRowView to project the schema of the underlying rows. A simple implementation of ICustomTypeDescriptor is provided by the CustomTypeDescriptor class.

    Note

    To support design-time binding to types that implement ICustomTypeDescriptor, the type must also implement IComponent and exist as an instance on the Form.

  • IListSource interface

    A class that implements the IListSource interface enables list-based binding on non-list objects. The GetList method of IListSource is used to return a bindable list from an object that doesn't inherit from IList.IListSource is used by the DataSet class.

  • IRaiseItemChangedEvents interface

    A class that implements the IRaiseItemChangedEvents interface is a bindable list that also implements the IBindingList interface. This interface is used to indicate if your type raises ListChanged events of type ItemChanged through its RaisesItemChangedEvents property.

    Note

    You should implement the IRaiseItemChangedEvents if your data source provides the property to list event conversion described previously and is interacting with the BindingSource component. Otherwise, the BindingSource will also perform property to list event conversion resulting in slower performance.

  • ISupportInitialize interface

    A component that implements the ISupportInitialize interface takes advantages of batch optimizations for setting properties and initializing co-dependent properties. The ISupportInitialize contains two methods:

    • BeginInit signals that object initialization is starting.

    • EndInit signals that object initialization is finishing.

  • ISupportInitializeNotification interface

    A component that implements the ISupportInitializeNotification interface also implements the ISupportInitialize interface. This interface allows you to notify other ISupportInitialize components that initialization is complete. The ISupportInitializeNotification interface contains two members:

  • INotifyPropertyChanged interface

    A class that implements this interface is a type that raises an event when any of its property values change. This interface is designed to replace the pattern of having a change event for each property of a control. When used in a BindingList<T>, a business object should implement the INotifyPropertyChanged interface and the BindingList`1 will convert PropertyChanged events to ListChanged events of type ItemChanged.

    Note

    For change notification to occur in a binding between a bound client and a data source, your bound data-source type should either implement the INotifyPropertyChanged interface (preferred) or you can provide propertyNameChanged events for the bound type, but you shouldn't do both.

Interfaces for implementation by component authors

The following interfaces are designed for consumption by the Windows Forms data-binding engine:

Data sources supported by Windows Forms

Traditionally, data binding has been used within applications to take advantage of data stored in databases. With Windows Forms data binding, you can access data from databases and data in other structures, such as arrays and collections, so long as certain minimum requirements have been met.

Structures to bind To

In Windows Forms, you can bind to a wide variety of structures, from simple objects (simple binding) to complex lists such as ADO.NET data tables (complex binding). For simple binding, Windows Forms support binding to the public properties on the simple object. Windows Forms list-based binding generally requires that the object supports the IList interface or the IListSource interface. Additionally, if you're binding with through a BindingSource component, you can bind to an object that supports the IEnumerable interface.

The following list shows the structures you can bind to in Windows Forms.

  • BindingSource

    A BindingSource is the most common Windows Forms data source and acts a proxy between a data source and Windows Forms controls. The general BindingSource usage pattern is to bind your controls to the BindingSource and bind the BindingSource to the data source (for example, an ADO.NET data table or a business object). The BindingSource provides services that enable and improve the level of data binding support. For example, Windows Forms list based controls such as the DataGridView and ComboBox don't directly support binding to IEnumerable data sources however, you can enable this scenario by binding through a BindingSource. In this case, the BindingSource will convert the data source to an IList.

  • Simple objects

    Windows Forms support data binding control properties to public properties on the instance of an object using the Binding type. Windows Forms also support binding list based controls, such as a ListControl to an object instance when a BindingSource is used.

  • Array or Collection

    To act as a data source, a list must implement the IList interface; one example would be an array that is an instance of the Array class. For more information on arrays, see How to: Create an Array of Objects (Visual Basic).

    In general, you should use BindingList<T> when you create lists of objects for data binding. BindingList is a generic version of the IBindingList interface. The IBindingList interface extends the IList interface by adding properties, methods and events necessary for two-way data binding.

  • IEnumerable

    Windows Forms controls can be bound to data sources that only support the IEnumerable interface if they're bound through a BindingSource component.

  • ADO.NET data objects

    ADO.NET provides many data structures suitable for binding to. Each varies in its sophistication and complexity.

    • DataColumn

      A DataColumn is the essential building block of a DataTable, in that multiple columns comprise a table. Each DataColumn has a DataType property that determines the kind of data the column holds (for example, the make of an automobile in a table describing cars). You can simple-bind a control (such as a TextBox control's Text property) to a column within a data table.

    • DataTable

      A DataTable is the representation of a table, with rows and columns, in ADO.NET. A data table contains two collections: DataColumn, representing the columns of data in a given table (which ultimately determine the kinds of data that can be entered into that table), and DataRow, representing the rows of data in a given table. You can complex-bind a control to the information contained in a data table (such as binding the DataGridView control to a data table). However, when you bind to a DataTable, you're a binding to the table's default view.

    • DataView

      A DataView is a customized view of a single data table that may be filtered or sorted. A data view is the data "snapshot" used by complex-bound controls. You can simple-bind or complex-bind to the data within a data view, but note that you're binding to a fixed "picture" of the data rather than a clean, updating data source.

    • DataSet

      A DataSet is a collection of tables, relationships, and constraints of the data in a database. You can simple-bind or complex-bind to the data within a dataset, but note that you're binding to the default DataViewManager for the DataSet (see the next bullet point).

    • DataViewManager

      A DataViewManager is a customized view of the entire DataSet, analogous to a DataView, but with relations included. With a DataViewSettings collection, you can set default filters and sort options for any views that the DataViewManager has for a given table.

Types of data binding

Windows Forms can take advantage of two types of data binding: simple binding and complex binding. Each offers different advantages.

Type of data binding Description
Simple data binding The ability of a control to bind to a single data element, such as a value in a column in a dataset table. Simple data binding is the type of binding typical for controls such as a TextBox control or Label control, which are controls that typically only display a single value. In fact, any property on a control can be bound to a field in a database. There's extensive support for this feature in Visual Studio.

For more information, see Navigate data and Create a simple-bound control (Windows Forms .NET).
Complex data binding The ability of a control to bind to more than one data element, typically more than one record in a database. Complex binding is also called list-based binding. Examples of controls that support complex binding are the DataGridView, ListBox, and ComboBox controls. For an example of complex data binding, see How to: Bind a Windows Forms ComboBox or ListBox Control to Data.

Binding source component

To simplify data binding, Windows Forms enables you to bind a data source to the BindingSource component and then bind controls to the BindingSource. You can use the BindingSource in simple or complex binding scenarios. In either case, the BindingSource acts as an intermediary between the data source and bound controls providing change notification currency management and other services.

Common scenarios that employ data binding

Nearly every commercial application uses information read from data sources of one type or another, usually through data binding. The following list shows a few of the most common scenarios that utilize data binding as the method of data presentation and manipulation.

Scenario Description
Reporting Reports provide a flexible way for you to display and summarize your data in a printed document. It's common to create a report that prints selected contents of a data source either to the screen or to a printer. Common reports include lists, invoices, and summaries. Items are formatted into columns of lists, with subitems organized under each list item, but you should choose the layout that best suits the data.
Data entry A common way to enter large amounts of related data or to prompt users for information is through a data entry form. Users can enter information or select choices using text boxes, option buttons, drop-down lists, and check boxes. Information is then submitted and stored in a database, whose structure is based on the information entered.
Master/detail relationship A master/detail application is one format for looking at related data. Specifically, there are two tables of data with a relation connecting in the classic business example, a "Customers" table and an "Orders" table with a relationship between them linking customers and their respective orders. For more information about creating a master/detail application with two Windows Forms DataGridView controls, see How to: Create a Master/Detail Form Using Two Windows Forms DataGridView Controls
Lookup Table Another common data presentation/manipulation scenario is the table lookup. Often, as part of a larger data display, a ComboBox control is used to display and manipulate data. The key is that the data displayed in the ComboBox control is different than the data written to the database. For example, if you have a ComboBox control displaying the items available from a grocery store, you would probably like to see the names of the products (bread, milk, eggs). However, to ease information retrieval within the database and for database normalization, you would probably store the information for the specific items of a given order as item numbers (#501, #603, and so on). Thus, there's an implicit connection between the "friendly name" of the grocery item in the ComboBox control on your form and the related item number that is present in an order. It's the essence of a table lookup. For more information, see How to: Create a Lookup Table with the Windows Forms BindingSource Component.

See also