Namespace:
System.Windows.Forms
Assembly:
System.Windows.Forms (in System.Windows.Forms.dll)
Visual Basic (Declaration)
Public Class BindingContext _
Implements ICollection, IEnumerable
Dim instance As BindingContext
public class BindingContext : ICollection,
IEnumerable
public ref class BindingContext : ICollection,
IEnumerable
public class BindingContext implements ICollection, IEnumerable
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")
textBox1.DataBindings.Add("Text", dataSet1, "Customers.FirstName");
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")
textBox2.DataBindings.Add("Text", dataSet1, "Customers.LastName");
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;
comboBox1.DisplayMember = "Customers.FirstName";
this.BindingContext[dataSet1, "Customers"].Position = 1;
comboBox1->DataSource = dataSet1;
comboBox1->DisplayMember = "Customers.FirstName";
this->BindingContext->get_Item(dataSet1, "Customers")->Position = 1;
ComboBox1.DataSource = DataSet1.Customers
ComboBox1.DisplayMember = "FirstName"
Me.BindingContext(dataSet1.Customers).Position = 1
comboBox1.DataSource = DataSet1.Customers;
comboBox1.DisplayMember = "FirstName";
this.BindingContext[dataSet1.Customers].Position = 1;
comboBox1->DataSource = dataSet1->Customers;
comboBox1->DisplayMember = "FirstName";
this->BindingContext->get_Item(dataSet1->Customers)->Position = 1;
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)
text3.DataBindings.Add(b)
' 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
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");
}
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( gcnew Binding( "Text",ds,"customers.custName" ) );
text2->DataBindings->Add( gcnew 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( gcnew 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 = gcnew Binding( "Text",ds,"customers.custToOrders.OrderAmount" );
b->Parse += gcnew ConvertEventHandler( this, &Form1::CurrencyStringToDecimal );
b->Format += gcnew ConvertEventHandler( this, &Form1::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" );
}
protected function 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. */
var b : Binding = new Binding
("Text", ds, "customers.custToOrders.OrderAmount");
b.add_Parse(CurrencyStringToDecimal);
b.add_Format(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"];
}
private function DecimalToCurrencyString(sender, cevent : ConvertEventArgs)
{
/* This method is the Format event handler. Whenever the
control displays a new value, the value is converted from
its native Decimal type to a string. The ToString method
then formats the value as a Currency, by using the
formatting character "c". */
// We can only convert to string type.
if(cevent.DesiredType != String.GetType()) return;
cevent.Value = (Decimal(cevent.Value)).ToString("c");
}
private function CurrencyStringToDecimal(sender, cevent : ConvertEventArgs)
{
/* This method is the Parse event-handler. The Parse event
occurs whenever the displayed value changes. The static
ToDecimal method of the Convert class converts the
value back to its native Decimal type. */
// Can only convert to Decimal type.
if(cevent.DesiredType != Decimal.GetType()) return;
cevent.Value = Decimal.Parse(cevent.Value.ToString(),
NumberStyles.Currency, null);
/* To see that no precision is lost, print the unformatted
value. For example, changing a value to "10.0001"
causes the control to display "10.00", but the
unformatted value remains "10.0001". */
Console.WriteLine(cevent.Value);
}
protected function button1_Click(sender, e : System.EventArgs)
{
// Go to the previous item in the Customer list.
bmCustomers.Position -= 1;
}
protected function button2_Click(sender, e : System.EventArgs)
{
// Go to the next item in the Customer list.
bmCustomers.Position += 1;
}
protected function button3_Click(sender, e : System.EventArgs)
{
// Go to the previous item in the Orders list.
bmOrders.Position-=1;
}
protected function button4_Click(sender, e : System.EventArgs)
{
// Go to the next item in the Orders list.
bmOrders.Position+=1;
}
// Create a DataSet with two tables and populate it.
private function MakeDataSet()
{
// Create a DataSet.
ds = new DataSet("myDataSet");
// Create two DataTables.
var tCust : DataTable = new DataTable("Customers");
var tOrders : DataTable= new DataTable("Orders");
// Create two columns, and add them to the first table.
var cCustID : DataColumn = new DataColumn("CustID", Int32);
var cCustName : DataColumn = new DataColumn("CustName");
tCust.Columns.Add(cCustID);
tCust.Columns.Add(cCustName);
// Create three columns, and add them to the second table.
var cID : DataColumn =
new DataColumn("CustID", Int32);
var cOrderDate : DataColumn =
new DataColumn("orderDate", DateTime);
var cOrderAmount : DataColumn =
new DataColumn("OrderAmount", Decimal);
tOrders.Columns.Add(cOrderAmount);
tOrders.Columns.Add(cID);
tOrders.Columns.Add(cOrderDate);
// Add the tables to the DataSet.
ds.Tables.Add(tCust);
ds.Tables.Add(tOrders);
// Create a DataRelation, and add it to the DataSet.
var dr : DataRelation = new DataRelation
("custToOrders", cCustID , cID);
ds.Relations.Add(dr);
/* Populate the tables. For each customer and order,
create need two DataRow variables. */
var newRow1 : DataRow;
var newRow2 : DataRow;
// Create three customers in the Customers Table.
for(var i : int = 1; i < 4; i++)
{
newRow1 = tCust.NewRow();
newRow1["custID"] = i;
// Add the row to the Customers table.
tCust.Rows.Add(newRow1);
}
// Give each customer a distinct name.
tCust.Rows[0]["custName"] = "Alpha";
tCust.Rows[1]["custName"] = "Beta";
tCust.Rows[2]["custName"] = "Omega";
// For each customer, create five rows in the Orders table.
for(var j : int = 1; j < 4; j++)
{
for(var k : int = 1; k < 6; k++)
{
newRow2 = tOrders.NewRow();
newRow2["CustID"]= j;
newRow2["orderDate"]= new DateTime(2001, j, k * 2);
newRow2["OrderAmount"] = j * 10 + k * .1;
// Add the row to the Orders table.
tOrders.Rows.Add(newRow2);
}
}
}
}
System..::.Object
System.Windows.Forms..::.BindingContext
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
.NET Framework
Supported in: 3.5, 3.0, 2.0, 1.1, 1.0
.NET Compact Framework
Supported in: 3.5, 2.0, 1.0
Reference