BindingContext-Klasse
Verwaltet die Auflistung von BindingManagerBase-Objekten für ein beliebiges Objekt, das von der Control-Klasse erbt.
Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in system.windows.forms.dll)
Syntax
'Declaration
Public Class BindingContext
Implements ICollection, IEnumerable
'Usage
Dim instance As BindingContext
public class BindingContext : ICollection, IEnumerable
public ref class BindingContext : ICollection, IEnumerable
public class BindingContext implements ICollection, IEnumerable
public class BindingContext implements ICollection, IEnumerable
Hinweise
Jede Windows Form verfügt über mindestens ein BindingContext-Objekt, das die BindingManagerBase-Objekte für das Formular verwaltet. Da die BindingManagerBase-Klasse abstrakt ist, ist der Rückgabetyp der Item-Eigenschaft entweder ein CurrencyManager oder ein PropertyManager. Wenn die Datenquelle ein Objekt ist, das keine Objektliste, sondern nur eine einzelne Eigenschaft zurückgeben kann, dann ist Type ein PropertyManager. Wenn Sie z. B. TextBox als Datenquelle angeben, wird PropertyManager zurückgegeben. Wenn die Datenquelle jedoch ein Objekt ist, das IList oder IBindingList implementiert, wird ein CurrencyManager zurückgegeben.
Für jede Datenquelle auf einer Windows Form gibt es einen einzelnen CurrencyManager oder PropertyManager. Da einem Windows Form mehrere Datenquelle zugeordnet sein können, ermöglicht es der BindingContext, einen bestimmten CurrencyManager abzurufen, der einer Datenquelle zugeordnet ist.
Hinweis
Wenn die Item-Eigenschaft verwendet wird, erstellt der BindingContext eine neue BindingManagerBase, sofern nicht bereits vorhanden. Dies kann zu unerwünschten Ergebnissen führen, da das zurückgegebene Objekt möglicherweise nicht die vorgesehene Liste oder Listen verwaltet. Um die Rückgabe einer ungültigen BindingManagerBase zu verhindern, ermitteln Sie mit der Contains-Methode, ob die beabsichtigte BindingManagerBase bereits vorhanden ist.
Wenn Sie datengebundene Steuerelemente in ein Container-Steuerelement wie GroupBox, Panel oder TabControl einbinden, können Sie einen BindingContext für ausschließlich dieses Container-Steuerelement und dessen Steuerelemente erstellen. Dann kann jeder Teil des Formulars von seiner eigenen BindingManagerBase verwaltet werden. Weitere Informationen über das Erstellen mehrerer BindingManagerBase-Objekte für dieselbe Datenquelle finden Sie unter dem BindingContext-Konstruktor.
Wenn Sie einem Formular ein TextBox-Steuerelement hinzufügen und an eine Spalte einer Tabelle im DataSet binden, kommuniziert das Steuerelement mit dem BindingContext dieses Formulars. Der BindingContext kommuniziert dann wiederum mit dem bestimmten CurrencyManager für diese Datenzuordnung. Wenn Sie die Position-Eigenschaft des CurrencyManager abrufen, meldet dieser den aktuellen Datensatz für die Bindung dieses TextBox-Steuerelements. Im folgenden Codebeispiel wird ein TextBox-Steuerelement an die Spalte FirstName der Tabelle Customers im DataSet dataSet1 über den BindingContext für das Formular gebunden, in dem es sich befindet.
TextBox1.DataBindings.Add("Text", dataSet1, "Customers.FirstName")
textBox1.DataBindings.Add("Text", dataSet1, "Customers.FirstName");
textBox1->DataBindings->Add("Text", dataSet1, "Customers.FirstName");
Sie können dem Formular ein zweites TextBox-Steuerelement (TextBox2) hinzufügen und an die Spalte LastName der Tabelle Customers im gleichen DataSet binden. Der BindingContext erkennt die erste Bindung (von TextBox1 an Customers.FirstName), sodass der gleiche CurrencyManager verwendet wird, da beide Textfelder an das gleiche DataSet (DataSet1) gebunden sind.
TextBox2.DataBindings.Add("Text", dataSet1, "Customers.LastName")
textBox2.DataBindings.Add("Text", dataSet1, "Customers.LastName");
textBox2->DataBindings->Add("Text", dataSet1, "Customers.LastName");
Wenn Sie TextBox2 an ein anderes Dataset binden, erstellt und verwaltet der BindingContext einen zweiten CurrencyManager.
Beim Festlegen der DataSource-Eigenschaft und der DisplayMember-Eigenschaft ist Konsistenz von großer Bedeutung. Andernfalls erstellt der BindingContext mehrere Datensatzzeigerverwaltungen für das gleiche DataSet, was zu Fehlern führt. Im folgenden Codebeispiel werden einige Möglichkeiten veranschaulicht, die Eigenschaften und ihre zugeordneten BindingContext-Objekte festzulegen. Sie können die Eigenschaften mit jeder der folgenden Methoden festlegen, solange diese konsequent im gesamten Code verwendet wird.
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;
Hinweis
Die meisten Windows Forms-Anwendungen binden über eine BindingSource. Die BindingSource-Komponente kapselt einen CurrencyManager und macht die CurrencyManager-Programmierschnittstelle verfügbar. Wenn Sie eine BindingSource für die Bindung verwenden, sollten Sie die von der BindingSource verfügbar gemachten Member verwenden, um den Datensatzzeiger (d. h. die Position) zu ändern, und nicht die des BindingContext.
Beispiel
Im folgenden Codebeispiel werden vier Binding-Objekte erstellt, um fünf Steuerelemente, d. h. ein DateTimePicker-Steuerelement und vier TextBox-Steuerelemente, an verschiedene Datenquellen zu binden. Mithilfe von BindingContext wird dann die BindingManagerBase für jede Datenquelle abgerufen.
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 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.get_DataBindings().Add(new Binding("Text", ds,
"customers.custName"));
text2.get_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.get_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.add_Parse(new ConvertEventHandler(CurrencyStringToDecimal));
b.add_Format(new ConvertEventHandler(DecimalToCurrencyString));
text3.get_DataBindings().Add(b);
// Get the BindingManagerBase for the Customers table.
bmCustomers = this.get_BindingContext().get_Item(ds, "Customers");
/* Get the BindingManagerBase for the Orders table using the
RelationName.
*/
bmOrders = this.get_BindingContext().get_Item(ds,
"customers.CustToOrders");
/* Bind the fourth TextBox control's Text property to the
third control's Text property.
*/
text4.get_DataBindings().Add("Text", text3, "Text");
} //BindControls
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);
}
}
}
}
Vererbungshierarchie
System.Object
System.Windows.Forms.BindingContext
Threadsicherheit
Alle öffentlichen statischen (Shared in Visual Basic) Member dieses Typs sind threadsicher. Bei Instanzmembern ist die Threadsicherheit nicht gewährleistet.
Plattformen
Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile für Pocket PC, Windows Mobile für Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
.NET Framework unterstützt nicht alle Versionen sämtlicher Plattformen. Eine Liste der unterstützten Versionen finden Sie unter Systemanforderungen.
Versionsinformationen
.NET Framework
Unterstützt in: 2.0, 1.1, 1.0
.NET Compact Framework
Unterstützt in: 2.0, 1.0
Siehe auch
Referenz
BindingContext-Member
System.Windows.Forms-Namespace
BindingManagerBase
Binding-Klasse
BindingsCollection