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BindingContext Class

Manages the collection of BindingManagerBase objects for any object that inherits from the Control class.


Namespace:  System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

Public Class BindingContext _
	Implements ICollection, IEnumerable

The BindingContext type exposes the following members.

Public methodBindingContextInitializes a new instance of the BindingContext class.

Public propertyIsReadOnlyInfrastructure. Gets a value indicating whether the collection is read-only.
Public propertyItem(Object)Gets the BindingManagerBase that is associated with the specified data source.
Public propertyItem(Object, String)Gets a BindingManagerBase that is associated with the specified data source and data member.

Protected methodAddAdds the BindingManagerBase associated with a specific data source to the collection.
Protected methodAddCoreInfrastructure. Adds the BindingManagerBase associated with a specific data source to the collection.
Protected methodClearClears the collection of any BindingManagerBase objects.
Protected methodClearCoreInfrastructure. Clears the collection.
Public methodContains(Object)Gets a value indicating whether the BindingContext contains the BindingManagerBase associated with the specified data source.
Public methodContains(Object, String)Gets a value indicating whether the BindingContext contains the BindingManagerBase associated with the specified data source and data member.
Public methodEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Protected methodOnCollectionChangedInfrastructure. Raises the CollectionChanged event.
Protected methodRemoveDeletes the BindingManagerBase associated with the specified data source.
Protected methodRemoveCoreInfrastructure. Removes the BindingManagerBase associated with the specified data source.
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
Public methodStatic memberUpdateBindingAssociates a Binding with a new BindingContext.

Public eventCollectionChangedInfrastructure. Always raises a NotImplementedException when handled.

Public Extension MethodAsParallelEnables parallelization of a query. (Defined by ParallelEnumerable.)
Public Extension MethodAsQueryableConverts an IEnumerable to an IQueryable. (Defined by Queryable.)
Public Extension MethodCast(Of TResult)Casts the elements of an IEnumerable to the specified type. (Defined by Enumerable.)
Public Extension MethodOfType(Of TResult)Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.)

Explicit interface implemetationPrivate methodICollection.CopyToInfrastructure. Copies the elements of the collection into a specified array, starting at the collection index.
Explicit interface implemetationPrivate propertyICollection.CountInfrastructure. Gets the total number of CurrencyManager objects managed by the BindingContext.
Explicit interface implemetationPrivate propertyICollection.IsSynchronizedInfrastructure. Gets a value indicating whether the collection is synchronized.
Explicit interface implemetationPrivate propertyICollection.SyncRootInfrastructure. Gets an object to use for synchronization (thread safety).
Explicit interface implemetationPrivate methodIEnumerable.GetEnumeratorInfrastructure. Gets an enumerator for the collection.

Each Windows Form has at least one BindingContext object that manages the BindingManagerBase objects for the form. Because the BindingManagerBase class is abstract, the return type of the Item property is either a CurrencyManager or a PropertyManager. If the data source is an object that can return only a single property (instead of a list of objects), the Type is a PropertyManager. For example, if you specify a TextBox as the data source, a PropertyManager is returned. On the other hand, if the data source is an object that implements IList or IBindingList, a CurrencyManager is returned.

For each data source on a Windows Form, there is a single CurrencyManager or PropertyManager. Because there may be multiple data sources associated with a Windows Form, the BindingContext enables you to retrieve any particular CurrencyManager associated with a data source.


When using the Item property, the BindingContext creates a new BindingManagerBase if one does not already exist. This can lead to some confusion, as the returned object may not manage the list (or any list) that you intend. To prevent returning an invalid BindingManagerBase, use the Contains method to determine if the intended BindingManagerBase already exists.

If you use a container control, such as a GroupBox, Panel, or TabControl, to contain data-bound controls, you can create a BindingContext for just that container control and its controls. Then, each part of your form can be managed by its own BindingManagerBase. See the BindingContext constructor for more information about creating multiple BindingManagerBase objects for the same data source.

If you add a TextBox control to a form and bind it to a column of a table in a dataset, the control communicates with the BindingContext of that form. The BindingContext, in turn, talks to the specific CurrencyManager for that data association. If you queried the Position property of the CurrencyManager, it would report the current record for the binding of that TextBox control. In the following code example, a TextBox control is bound to the FirstName column of a Customers table on the dataSet1 dataset through the BindingContext for the form it is on.

TextBox1.DataBindings.Add("Text", dataSet1, "Customers.FirstName")

You can add a second TextBox control (TextBox2) to the form and bind it to the LastName column of the Customers table in the same dataset. The BindingContext is aware of the first binding (TextBox1 to Customers.FirstName), so it would use the same CurrencyManager, as both text boxes are bound to the same dataset (DataSet1).

TextBox2.DataBindings.Add("Text", dataSet1, "Customers.LastName")

If you bind TextBox2 to a different dataset, the BindingContext creates and manages a second CurrencyManager.

It is important to be consistent about how you set the DataSource and DisplayMember properties; otherwise, the BindingContext creates multiple currency managers for the same dataset, which results in errors. The following code example shows a few ways to set the properties and their associated BindingContext objects. You can set the properties using either of the following methods, as long as you are consistent throughout your code.

ComboBox1.DataSource = DataSet1
ComboBox1.DisplayMember = "Customers.FirstName"
Me.BindingContext(dataSet1, "Customers").Position = 1
ComboBox1.DataSource = DataSet1.Customers
ComboBox1.DisplayMember = "FirstName"
Me.BindingContext(dataSet1.Customers).Position = 1

Most Windows Forms applications bind through a BindingSource. The BindingSource component encapsulates a CurrencyManager and exposes the CurrencyManager programming interface. When using a BindingSource for binding, you should use the members exposed by the BindingSource to manipulate "currency" (that is, Position) rather than go through the BindingContext.

The following code example creates four Binding objects to bind five controls—a DateTimePicker and four TextBox controls—to several data sources. The BindingContext is then used to get the BindingManagerBase for each data source.

Protected Sub BindControls()

      ' Create two Binding objects for the first two TextBox  
      '   controls. The data-bound property for both controls  
      '   is the Text property. The data source is a DataSet  
      '   (ds). The data member is the string  
      '   "TableName.ColumnName".
      text1.DataBindings.Add(New Binding _
         ("Text", ds, "customers.custName"))
      text2.DataBindings.Add(New Binding _
         ("Text", ds, "customers.custID"))

      ' Bind the DateTimePicker control by adding a new Binding.  
      '   The data member of the DateTimePicker is a  
      '   TableName.RelationName.ColumnName string.
      DateTimePicker1.DataBindings.Add(New Binding _
         ("Value", ds, "customers.CustToOrders.OrderDate"))

      ' Add event delegates for the Parse and Format events to a  
      '   new Binding object, and add the object to the third  
      '   TextBox control's BindingsCollection. The delegates  
      '   must be added before adding the Binding to the  
      '   collection; otherwise, no formatting occurs until  
      '   the Current object of the BindingManagerBase for  
      '   the data source changes. 
      Dim b As Binding = New Binding _
         ("Text", ds, "customers.custToOrders.OrderAmount")
      AddHandler b.Parse,  New ConvertEventHandler(AddressOf CurrencyStringToDecimal)      
      AddHandler b.Format, New ConvertEventHandler(AddressOf DecimalToCurrencyString)

      ' Get the BindingManagerBase for the Customers table.
      bmCustomers = Me.BindingContext(ds, "Customers")

      ' Get the BindingManagerBase for the Orders table using the  
      '   RelationName.
      bmOrders = Me.BindingContext(ds, "customers.CustToOrders")

      ' Bind the fourth TextBox control's Text property to the 
      ' third control's Text property.
      text4.DataBindings.Add("Text", text3, "Text")

   End Sub

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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