BindingContext Class

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.

Note
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";
this.BindingContext[dataSet1, "Customers"].Position = 1;

comboBox1.DataSource = DataSet1.Customers;
comboBox1.DisplayMember = "FirstName";
this.BindingContext[dataSet1.Customers].Position = 1;

Note
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 void 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 a navigation path in the form: 
         "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 navigation path:
         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. */
         Binding b = new Binding
         ("Text", ds, "customers.custToOrders.OrderAmount");
      b.Parse+=new ConvertEventHandler(CurrencyStringToDecimal);
      b.Format+=new ConvertEventHandler(DecimalToCurrencyString);
      text3.DataBindings.Add(b);

      // Get the BindingManagerBase for the Customers table. 
      bmCustomers = this.BindingContext [ds, "Customers"];

      /* Get the BindingManagerBase for the Orders table using the 
         RelationName. */ 
      bmOrders = this.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");
   }

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference