docs-desktop/dotnet-desktop-guide/framework/winforms/controls/bindingsource-component-architecture.md

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BindingSource Component Architecture	03/30/2017	BindingSource component [Windows Forms], architecture Windows Forms, data binding BindingSource component [Windows Forms], about BindingSource component data binding [Windows Forms], BindingSource component	7bc69c90-8a11-48b1-9336-3adab5b41591

BindingSource Component Architecture

With the xref:System.Windows.Forms.BindingSource component, you can universally bind all Windows Forms controls to data sources.

The xref:System.Windows.Forms.BindingSource component simplifies the process of binding controls to a data source and provides the following advantages over traditional data binding:

• Enables design-time binding to business objects.

• Encapsulates xref:System.Windows.Forms.CurrencyManager functionality and exposes xref:System.Windows.Forms.CurrencyManager events at design time.

• Simplifies creating a list that supports the xref:System.ComponentModel.IBindingList interface by providing list change notification for data sources that do not natively support list change notification.

• Provides an extensibility point for the xref:System.ComponentModel.IBindingList.AddNew%2A?displayProperty=nameWithType method.

• Provides a level of indirection between the data source and the control. This indirection is important when the data source may change at run time.

• Interoperates with other data-related Windows Forms controls, specifically the xref:System.Windows.Forms.BindingNavigator and the xref:System.Windows.Forms.DataGridView controls.

For these reasons, the xref:System.Windows.Forms.BindingSource component is the preferred way to bind your Windows Forms controls to data sources.

BindingSource Features

The xref:System.Windows.Forms.BindingSource component provides several features for binding controls to data. With these features, you can implement most data-binding scenarios with almost no coding on your part.

The xref:System.Windows.Forms.BindingSource component accomplishes this by providing a consistent interface for accessing many different kinds of data sources. This means that you use the same procedure for binding to any type. For example, you can attach the xref:System.Windows.Forms.BindingSource.DataSource%2A property to a xref:System.Data.DataSet or to a business object and in both cases you use the same set of properties, methods, and events to manipulate the data source.

The consistent interface provided by the xref:System.Windows.Forms.BindingSource component greatly simplifies the process of binding data to controls. For data-source types that provide change notification, the xref:System.Windows.Forms.BindingSource component automatically communicates changes between the control and the data source. For data-source types that do not provide change notification, events are provided that let you raise change notifications. The following list shows the features supported by the xref:System.Windows.Forms.BindingSource component:

• Indirection.

• Currency management.

• Data source as a list.

• xref:System.Windows.Forms.BindingSource as an xref:System.ComponentModel.IBindingList.

• Custom item creation.

• Transactional item creation.

• xref:System.Collections.IEnumerable support.

• Design-time support.

• Static xref:System.Windows.Forms.ListBindingHelper methods.

• Sorting and filtering with the xref:System.ComponentModel.IBindingListView interface.

• Integration with xref:System.Windows.Forms.BindingNavigator.

Indirection

The xref:System.Windows.Forms.BindingSource component provides a level of indirection between a control and a data source. Instead of binding a control directly to a data source, you bind the control to a xref:System.Windows.Forms.BindingSource, and you attach the data source to the xref:System.Windows.Forms.BindingSource component's xref:System.Windows.Forms.BindingSource.DataSource%2A property.

With this level of indirection, you can change the data source without resetting the control binding. This gives you the following capabilities:

• You can attach the xref:System.Windows.Forms.BindingSource to different data sources while retaining the current control bindings.

• You can change items in the data source and notify bound controls. For more information, see How to: Reflect Data Source Updates in a Windows Forms Control with the BindingSource.

• You can bind to a xref:System.Type instead of an object in memory. For more information, see How to: Bind a Windows Forms Control to a Type. You can then bind to an object at run time.

Currency Management

The xref:System.Windows.Forms.BindingSource component implements the xref:System.Windows.Forms.ICurrencyManagerProvider interface to handle currency management for you. With the xref:System.Windows.Forms.ICurrencyManagerProvider interface, you can also access to the currency manager for a xref:System.Windows.Forms.BindingSource, in addition to the currency manager for another xref:System.Windows.Forms.BindingSource bound to the same xref:System.Windows.Forms.BindingSource.DataMember%2A.

The xref:System.Windows.Forms.BindingSource component encapsulates xref:System.Windows.Forms.CurrencyManager functionality and exposes the most common xref:System.Windows.Forms.CurrencyManager properties and events. The following table describes some of the members related to currency management.

xref:System.Windows.Forms.ICurrencyManagerProvider.CurrencyManager%2A property
Gets the currency manager associated with the xref:System.Windows.Forms.BindingSource.

xref:System.Windows.Forms.ICurrencyManagerProvider.GetRelatedCurrencyManager%2A method
If there is another xref:System.Windows.Forms.BindingSource bound to the specified data member, gets its currency manager.

xref:System.Windows.Forms.BindingSource.Current%2A property
Gets the current item of the data source.

xref:System.Windows.Forms.BindingSource.Position%2A property
Gets or sets the current position in the underlying list.

xref:System.Windows.Forms.BindingSource.EndEdit%2A method
Applies pending changes to the underlying data source.

xref:System.Windows.Forms.BindingSource.CancelEdit%2A method
Cancels the current edit operation.

Data Source as a List

The xref:System.Windows.Forms.BindingSource component implements the xref:System.ComponentModel.IBindingListView and xref:System.ComponentModel.ITypedList interfaces. With this implementation, you can use the xref:System.Windows.Forms.BindingSource component itself as a data source, without any external storage.

When the xref:System.Windows.Forms.BindingSource component is attached to a data source, it exposes the data source as a list.

The xref:System.Windows.Forms.BindingSource.DataSource%2A property can be set to several data sources. These include types, objects, and lists of types. The resulting data source will be exposed as a list. The following table shows some of the common data sources and the resulting list evaluation.

DataSource property	List results
A null reference (Nothing in Visual Basic)	An empty xref:System.ComponentModel.IBindingList of objects. Adding an item sets the list to the type of the added item.
A null reference (Nothing in Visual Basic) with xref:System.Windows.Forms.BindingSource.DataMember%2A set	Not supported; raises xref:System.ArgumentException.
Non-list type or object of type "T"	An empty xref:System.ComponentModel.IBindingList of type "T".
Array instance	An xref:System.ComponentModel.IBindingList containing the array elements.
xref:System.Collections.IEnumerable instance	An xref:System.ComponentModel.IBindingList containing the xref:System.Collections.IEnumerable items
List instance containing type "T"	An xref:System.ComponentModel.IBindingList instance containing type "T".

Additionally, xref:System.Windows.Forms.BindingSource.DataSource%2A can be set to other list types, such as xref:System.ComponentModel.IListSource and xref:System.ComponentModel.ITypedList, and the xref:System.Windows.Forms.BindingSource will handle them appropriately. In this case, the type that is contained in the list should have a parameterless constructor.

BindingSource as an IBindingList

The xref:System.Windows.Forms.BindingSource component provides members for accessing and manipulating the underlying data as an xref:System.ComponentModel.IBindingList. The following table describes some of these members.

Member	Description
xref:System.Windows.Forms.BindingSource.List%2A property	Gets the list that results from the evaluation of the xref:System.Windows.Forms.BindingSource.DataSource%2A or xref:System.Windows.Forms.BindingSource.DataMember%2A properties.
xref:System.Windows.Forms.BindingSource.AddNew%2A method	Adds a new item to the underlying list. Applies to data sources that implement the xref:System.ComponentModel.IBindingList interface and allow adding items (that is, the xref:System.Windows.Forms.BindingSource.AllowNew%2A property is set to true).

Custom Item Creation

You can handle the xref:System.Windows.Forms.BindingSource.AddingNew event to provide your own item-creation logic. The xref:System.Windows.Forms.BindingSource.AddingNew event occurs before a new object is added to the xref:System.Windows.Forms.BindingSource. This event is raised after the xref:System.Windows.Forms.BindingSource.AddNew%2A method is called, but before the new item is added to the underlying list. By handling this event, you can provide custom item creation behavior without deriving from the xref:System.Windows.Forms.BindingSource class. For more information, see How to: Customize Item Addition with the Windows Forms BindingSource.

Transactional Item Creation

The xref:System.Windows.Forms.BindingSource component implements the xref:System.ComponentModel.ICancelAddNew interface, which enables transactional item creation. After a new item is provisionally created by using a call to xref:System.Windows.Forms.BindingSource.AddNew%2A, the addition may be committed or rolled back in the following ways:

• The xref:System.ComponentModel.ICancelAddNew.EndNew%2A method will explicitly commit the pending addition.

• Performing another collection operation, such as an insertion, removal, or move, will implicitly commit the pending addition.

• The xref:System.ComponentModel.ICancelAddNew.CancelNew%2A method will roll back the pending addition if the method has not already been committed.

IEnumerable Support

The xref:System.Windows.Forms.BindingSource component enables binding controls to xref:System.Collections.IEnumerable data sources. With this component, you can bind to a data source such as a xref:System.Data.SqlClient.SqlDataReader?displayProperty=nameWithType.

When an xref:System.Collections.IEnumerable data source is assigned to the xref:System.Windows.Forms.BindingSource component, the xref:System.Windows.Forms.BindingSource creates an xref:System.ComponentModel.IBindingList and adds the contents of the xref:System.Collections.IEnumerable data source to the list.

Design-Time Support

Some object types cannot be created at design time, such as objects created from a factory class, or objects returned by a Web service. You may sometimes have to bind your controls to these types at design time, even though there is no object in memory to which your controls can bind. You may, for example, need to label the column headers of a xref:System.Windows.Forms.DataGridView control with the names of your custom type's public properties.

To support this scenario, the xref:System.Windows.Forms.BindingSource component supports binding to a xref:System.Type. When you assign a xref:System.Type to the xref:System.Windows.Forms.BindingSource.DataSource%2A property, the xref:System.Windows.Forms.BindingSource component creates an empty xref:System.ComponentModel.BindingList%601 of xref:System.Type items. Any controls you subsequently bind to the xref:System.Windows.Forms.BindingSource component will be alerted to the presence of the properties or schema of your type at design time, or at run time. For more information, see How to: Bind a Windows Forms Control to a Type.

Static ListBindingHelper Methods

The xref:System.Windows.Forms.BindingContext?displayProperty=nameWithType, xref:System.Windows.Forms.CurrencyManager?displayProperty=nameWithType, and xref:System.Windows.Forms.BindingSource types all share common logic to generate a list from a DataSource/DataMember pair. Additionally, this common logic is publicly exposed for use by control authors and other third parties in the following static methods:

• xref:System.Windows.Forms.ListBindingHelper.GetListItemProperties%2A

• xref:System.Windows.Forms.ListBindingHelper.GetList%2A.

• xref:System.Windows.Forms.ListBindingHelper.GetListName%2A

• xref:System.Windows.Forms.ListBindingHelper.GetListItemType%2A

Sorting and Filtering with the IBindingListView Interface

The xref:System.Windows.Forms.BindingSource component implements the xref:System.ComponentModel.IBindingListView interface, which extends the xref:System.ComponentModel.IBindingList interface. The xref:System.ComponentModel.IBindingList offers single column sorting and the xref:System.ComponentModel.IBindingListView offers advanced sorting and filtering. With xref:System.ComponentModel.IBindingListView, you can sort and filter items in the data source, if the data source also implements one of these interfaces. The xref:System.Windows.Forms.BindingSource component does not provide a reference implementation of these members. Instead, calls are forwarded to the underlying list.

The following table describes the properties you use for sorting and filtering.

Member	Description
xref:System.Windows.Forms.BindingSource.Filter%2A property	If the data source is an xref:System.ComponentModel.IBindingListView, gets or sets the expression used to filter which rows are viewed.
xref:System.Windows.Forms.BindingSource.Sort%2A property	If the data source is an xref:System.ComponentModel.IBindingList, gets or sets a column name used for sorting and sort order information. -or- If the data source is an xref:System.ComponentModel.IBindingListView and supports advanced sorting, gets multiple column names used for sorting and sort order

Integration with BindingNavigator

You can use the xref:System.Windows.Forms.BindingSource component to bind any Windows Forms control to a data source, but the xref:System.Windows.Forms.BindingNavigator control is designed specifically to work with the xref:System.Windows.Forms.BindingSource component. The xref:System.Windows.Forms.BindingNavigator control provides a user interface for controlling the xref:System.Windows.Forms.BindingSource component's current item. By default, the xref:System.Windows.Forms.BindingNavigator control provides buttons that correspond to the navigation methods on the xref:System.Windows.Forms.BindingSource component. For more information, see How to: Navigate Data with the Windows Forms BindingNavigator Control.

See also

• xref:System.Windows.Forms.BindingSource
• xref:System.Windows.Forms.BindingNavigator
• BindingSource Component Overview
• BindingNavigator Control
• Windows Forms Data Binding
• Controls to Use on Windows Forms
• How to: Bind a Windows Forms Control to a Type
• How to: Reflect Data Source Updates in a Windows Forms Control with the BindingSource