Binding Classe

Definição

public ref class Binding

[System.ComponentModel.TypeConverter(typeof(System.Windows.Forms.ListBindingConverter))]
public class Binding

[<System.ComponentModel.TypeConverter(typeof(System.Windows.Forms.ListBindingConverter))>]
type Binding = class

Public Class Binding

Herança

Object

Binding

Atributos

TypeConverterAttribute

Exemplos

O exemplo de código seguinte cria um Windows Form com vários controlos que demonstram ligação simples de dados. O exemplo cria um DataSet com duas tabelas nomeadas Customers e Orders, e uma DataRelation com nome custToOrders. Quatro controlos (a DateTimePicker e três TextBox controlos) são dados ligados a colunas nas tabelas. Para cada controlo, o exemplo cria e adiciona a Binding ao controlo através da DataBindings propriedade. O exemplo devolve a BindingManagerBase para cada tabela através da forma BindingContext. Quatro Button controlos incrementam ou diminuem a Position propriedade sobre os BindingManagerBase objetos.

#using <system.dll>
#using <system.data.dll>
#using <system.drawing.dll>
#using <system.windows.forms.dll>
#using <system.xml.dll>

using namespace System;
using namespace System::Data;
using namespace System::Drawing;
using namespace System::Globalization;
using namespace System::Windows::Forms;

#define null 0L
public ref class Form1: public Form
{
private:
   System::ComponentModel::Container^ components;
   Button^ button1;
   Button^ button2;
   Button^ button3;
   Button^ button4;
   TextBox^ text1;
   TextBox^ text2;
   TextBox^ text3;
   BindingManagerBase^ bmCustomers;
   BindingManagerBase^ bmOrders;
   DataSet^ ds;
   DateTimePicker^ DateTimePicker1;

public:
   Form1()
   {
      // Required for Windows Form Designer support.
      InitializeComponent();

      // Call SetUp to bind the controls.
      SetUp();
   }

private:
   void InitializeComponent()
   {
      // Create the form and its controls.
      this->components = gcnew System::ComponentModel::Container;
      this->button1 = gcnew Button;
      this->button2 = gcnew Button;
      this->button3 = gcnew Button;
      this->button4 = gcnew Button;
      this->text1 = gcnew TextBox;
      this->text2 = gcnew TextBox;
      this->text3 = gcnew TextBox;
      this->DateTimePicker1 = gcnew DateTimePicker;
      this->Text =  "Binding Sample";
      this->ClientSize = System::Drawing::Size( 450, 200 );
      button1->Location = System::Drawing::Point( 24, 16 );
      button1->Size = System::Drawing::Size( 64, 24 );
      button1->Text =  "<";
      button1->Click += gcnew System::EventHandler( this, &Form1::button1_Click );
      button2->Location = System::Drawing::Point( 90, 16 );
      button2->Size = System::Drawing::Size( 64, 24 );
      button2->Text =  ">";
      button2->Click += gcnew System::EventHandler( this, &Form1::button2_Click );
      button3->Location = System::Drawing::Point( 90, 100 );
      button3->Size = System::Drawing::Size( 64, 24 );
      button3->Text =  "<";
      button3->Click += gcnew System::EventHandler( this, &Form1::button3_Click );
      button4->Location = System::Drawing::Point( 150, 100 );
      button4->Size = System::Drawing::Size( 64, 24 );
      button4->Text =  ">";
      button4->Click += gcnew System::EventHandler( this, &Form1::button4_Click );
      text1->Location = System::Drawing::Point( 24, 50 );
      text1->Size = System::Drawing::Size( 150, 24 );
      text2->Location = System::Drawing::Point( 190, 50 );
      text2->Size = System::Drawing::Size( 150, 24 );
      text3->Location = System::Drawing::Point( 290, 150 );
      text3->Size = System::Drawing::Size( 150, 24 );
      DateTimePicker1->Location = System::Drawing::Point( 90, 150 );
      DateTimePicker1->Size = System::Drawing::Size( 200, 800 );
      this->Controls->Add( button1 );
      this->Controls->Add( button2 );
      this->Controls->Add( button3 );
      this->Controls->Add( button4 );
      this->Controls->Add( text1 );
      this->Controls->Add( text2 );
      this->Controls->Add( text3 );
      this->Controls->Add( DateTimePicker1 );
   }

public:
   ~Form1()
   {
      if ( components != nullptr )
      {
         delete components;
      }
   }

private:
   void SetUp()
   {
      // Create a DataSet with two tables and one relation.
      MakeDataSet();
      BindControls();
   }

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 the 
              "TableName.ColumnName" string. */
      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 
              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" ];
   }

private:
   void DecimalToCurrencyString( Object^ /*sender*/, ConvertEventArgs^ cevent )
   {
      /* 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". */
      // The application can only convert to string type. 
      if ( cevent->DesiredType != String::typeid )
            return;

      cevent->Value = (dynamic_cast<Decimal^>(cevent->Value))->ToString( "c" );
   }

   void CurrencyStringToDecimal( Object^ /*sender*/, ConvertEventArgs^ cevent )
   {
      /* 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::typeid )
            return;

      cevent->Value = Decimal::Parse( cevent->Value->ToString(), NumberStyles::Currency, nullptr );
      
      /* 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 );
   }

private:
   void button1_Click( Object^ /*sender*/, System::EventArgs^ /*e*/ )
   {
      // Go to the previous item in the Customer list.
      bmCustomers->Position -= 1;
   }

   void button2_Click( Object^ /*sender*/, System::EventArgs^ /*e*/ )
   {
      // Go to the next item in the Customer list.
      bmCustomers->Position += 1;
   }

   void button3_Click( Object^ /*sender*/, System::EventArgs^ /*e*/ )
   {
      
      // Go to the previous item in the Orders list.
      bmOrders->Position = bmOrders->Position - 1;
   }

   void button4_Click( Object^ /*sender*/, System::EventArgs^ /*e*/ )
   {
      
      // Go to the next item in the Orders list.
      bmOrders->Position = bmOrders->Position + 1;
   }

private:

   // Create a DataSet with two tables and populate it.
   void MakeDataSet()
   {
      // Create a DataSet.
      ds = gcnew DataSet( "myDataSet" );

      // Create two DataTables.
      DataTable^ tCust = gcnew DataTable( "Customers" );
      DataTable^ tOrders = gcnew DataTable( "Orders" );

      // Create two columns, and add them to the first table.
      DataColumn^ cCustID = gcnew DataColumn( "CustID",Int32::typeid );
      DataColumn^ cCustName = gcnew DataColumn( "CustName" );
      tCust->Columns->Add( cCustID );
      tCust->Columns->Add( cCustName );

      // Create three columns, and add them to the second table.
      DataColumn^ cID = gcnew DataColumn( "CustID",Int32::typeid );
      DataColumn^ cOrderDate = gcnew DataColumn( "orderDate",DateTime::typeid );
      DataColumn^ cOrderAmount = gcnew DataColumn( "OrderAmount",Decimal::typeid );
      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.
      DataRelation^ dr = gcnew DataRelation( "custToOrders",cCustID,cID );
      ds->Relations->Add( dr );
      
      /* Populate the tables. For each customer and order, 
              create two DataRow variables. */
      DataRow^ newRow1; // = new DataRow();

      DataRow^ newRow2; // = new DataRow();

      // Create three customers in the Customers Table.
      for ( int i = 1; i < 4; i++ )
      {
         newRow1 = tCust->NewRow();
         newRow1[ "custID" ] = i;
         
         // Add the row to the Customers table.
         tCust->Rows->Add( newRow1 );

      }
      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 ( int i = 1; i < 4; i++ )
      {
         for ( int j = 1; j < 6; j++ )
         {
            newRow2 = tOrders->NewRow();
            newRow2[ "CustID" ] = i;
            newRow2[ "orderDate" ] = System::DateTime( 2001, i, j * 2 );
            newRow2[ "OrderAmount" ] = i * 10 + j * .1;
            
            // Add the row to the Orders table.
            tOrders->Rows->Add( newRow2 );
         }
      }
   }
};

int main()
{
   Application::Run( gcnew Form1 );
}

using System;
using System.Data;
using System.Drawing;
using System.Globalization;
using System.Windows.Forms;

public class Form1 : System.Windows.Forms.Form
{
   private System.ComponentModel.Container components;
   private Button button1;
   private Button button2;
   private Button button3;
   private Button button4;
   private TextBox text1;
   private TextBox text2;
   private TextBox text3;

   private BindingManagerBase bmCustomers;
   private BindingManagerBase bmOrders;
   private DataSet ds;
   private DateTimePicker DateTimePicker1;

   public Form1()
   {
      // Required for Windows Form Designer support.
      InitializeComponent();
      // Call SetUp to bind the controls.
      SetUp();
   }
 
   private void InitializeComponent()
   {
      // Create the form and its controls.
      this.components = new System.ComponentModel.Container();
      this.button1 = new System.Windows.Forms.Button();
      this.button2 = new System.Windows.Forms.Button();
      this.button3 = new System.Windows.Forms.Button();
      this.button4 = new System.Windows.Forms.Button();
      
      this.text1= new System.Windows.Forms.TextBox();
      this.text2= new System.Windows.Forms.TextBox();
      this.text3= new System.Windows.Forms.TextBox();
      
      this.DateTimePicker1 = new DateTimePicker();
      
      this.Text = "Binding Sample";
      this.ClientSize = new System.Drawing.Size(450, 200);
      
      button1.Location = new System.Drawing.Point(24, 16);
      button1.Size = new System.Drawing.Size(64, 24);
      button1.Text = "<";
      button1.Click+=new System.EventHandler(button1_Click);

      button2.Location = new System.Drawing.Point(90, 16);
      button2.Size = new System.Drawing.Size(64, 24);
      button2.Text = ">";
      button2.Click+=new System.EventHandler(button2_Click);

      button3.Location = new System.Drawing.Point(90, 100);
      button3.Size = new System.Drawing.Size(64, 24);
      button3.Text = "<";
      button3.Click+=new System.EventHandler(button3_Click);

      button4.Location = new System.Drawing.Point(150, 100);
      button4.Size = new System.Drawing.Size(64, 24);
      button4.Text = ">";
      button4.Click+=new System.EventHandler(button4_Click);

      text1.Location = new System.Drawing.Point(24, 50);
      text1.Size = new System.Drawing.Size(150, 24);

      text2.Location = new System.Drawing.Point(190, 50);
      text2.Size = new System.Drawing.Size(150, 24);

      text3.Location = new System.Drawing.Point(290, 150);
      text3.Size = new System.Drawing.Size(150, 24);
      
      DateTimePicker1.Location = new System.Drawing.Point(90, 150);
      DateTimePicker1.Size = new System.Drawing.Size(200, 800);
      
      this.Controls.Add(button1);
      this.Controls.Add(button2);
      this.Controls.Add(button3);
      this.Controls.Add(button4);
      this.Controls.Add(text1);
      this.Controls.Add(text2);
      this.Controls.Add(text3);
      this.Controls.Add(DateTimePicker1);
   }

   protected override void Dispose( bool disposing ){
      if( disposing ){
         if (components != null){
            components.Dispose();}
      }
      base.Dispose( disposing );
   }
   public static void Main()
   {
      Application.Run(new Form1());
   }
   
   private void SetUp()
   {
      // Create a DataSet with two tables and one relation.
      MakeDataSet();
      BindControls();
   }

   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 the  
         "TableName.ColumnName" string. */
      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. */
      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"];
   }

   private void DecimalToCurrencyString(object sender, ConvertEventArgs cevent)
   {
      /* 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". */

      // The application can only convert to string type. 
      if(cevent.DesiredType != typeof(string)) return;

      cevent.Value = ((decimal) cevent.Value).ToString("c");
   }

   private void CurrencyStringToDecimal(object sender, ConvertEventArgs cevent)
   {   
      /* 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 != typeof(decimal)) 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);
   }

   private void button1_Click(object sender, System.EventArgs e)
   {
      // Go to the previous item in the Customer list.
      bmCustomers.Position -= 1;
   }

   private void button2_Click(object sender, System.EventArgs e)
   {
      // Go to the next item in the Customer list.
      bmCustomers.Position += 1;
   }
    
   private void button3_Click(object sender, System.EventArgs e)
   {
      // Go to the previous item in the Orders list.
      bmOrders.Position-=1;
   }

   private void button4_Click(object sender, System.EventArgs e)
   {
      // Go to the next item in the Orders list.
      bmOrders.Position+=1;
   }

   // Create a DataSet with two tables and populate it.
   private void MakeDataSet()
   {
      // Create a DataSet.
      ds = new DataSet("myDataSet");
      
      // Create two DataTables.
      DataTable tCust = new DataTable("Customers");
      DataTable tOrders = new DataTable("Orders");

      // Create two columns, and add them to the first table.
      DataColumn cCustID = new DataColumn("CustID", typeof(int));
      DataColumn cCustName = new DataColumn("CustName");
      tCust.Columns.Add(cCustID);
      tCust.Columns.Add(cCustName);

      // Create three columns, and add them to the second table.
      DataColumn cID = 
         new DataColumn("CustID", typeof(int));
      DataColumn cOrderDate = 
         new DataColumn("orderDate",typeof(DateTime));
      DataColumn cOrderAmount = 
         new DataColumn("OrderAmount", typeof(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.
      DataRelation dr = new DataRelation
      ("custToOrders", cCustID , cID);
      ds.Relations.Add(dr);
   
      /* Populate the tables. For each customer and order, 
         create two DataRow variables. */
      DataRow newRow1;
      DataRow newRow2;

      // Create three customers in the Customers Table.
      for(int i = 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(int i = 1; i < 4; i++)
      {
         for(int j = 1; j < 6; j++)
         {
            newRow2 = tOrders.NewRow();
            newRow2["CustID"]= i;
            newRow2["orderDate"]= new DateTime(2001, i, j * 2);
            newRow2["OrderAmount"] = i * 10 + j  * .1;
            // Add the row to the Orders table.
            tOrders.Rows.Add(newRow2);
         }
      }
   }
 }

Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Globalization
Imports System.Windows.Forms

Public Class Form1
   Inherits Form

   Private components As Container
   Private button1 As Button
   Private button2 As Button
   Private button3 As Button
   Private button4 As Button
   Private text1 As TextBox
   Private text2 As TextBox
   Private text3 As TextBox

   Private bmCustomers As BindingManagerBase
   Private bmOrders As BindingManagerBase
   Private ds As DataSet
   Private DateTimePicker1 As DateTimePicker
   
   Public Sub New
      ' Required for Windows Form Designer support.
      InitializeComponent
      ' Call SetUp to bind the controls.
      SetUp
   End Sub

   Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
      If disposing Then
         If (components IsNot Nothing) Then
            components.Dispose()
         End If
      End If
      MyBase.Dispose(disposing)
    End Sub


   Private Sub InitializeComponent
      ' Create the form and its controls.
      With Me
         .components = New Container
         .button1 = New Button
         .button2 = New Button
         .button3 = New Button
         .button4 = New Button
         .text1 = New TextBox
         .text2 = New TextBox
         .text3 = New TextBox

         .DateTimePicker1 = New DateTimePicker
         
         .Text = "Binding Sample"
         .ClientSize = New Size(450, 200)

         With .button1
            .Location = New Point(24, 16)
            .Size = New Size(64, 24)
            .Text = "<"
            AddHandler button1.click, AddressOf button1_Click
         End With
         
         
         With .button2
            .Location = New Point(90, 16)
            .Size = New Size(64, 24)
            .Text = ">"
            AddHandler button2.click, AddressOf button2_Click
         End With
         
         With .button3
            .Location = New Point(90, 100)
            .Size = New Size(64, 24)
            .Text = ">"
            AddHandler button3.click, AddressOf button3_Click
         End With

         With .button4
            .Location = New Point(150, 100)
            .Size = New Size(64, 24)
            .Text = ">"
            AddHandler button4.click, AddressOf button4_Click
         End With

         With .text1
            .Location = New Point(24, 50)
            .Size = New Size(150, 24)
         End With

         With .text2
            .Location = New Point(190, 50)
            .Size = New Size(150, 24)
         End With

         With .text3
            .Location = New Point(290, 150)
            .Size = New Size(150, 24)
         End With

            With .DateTimePicker1
               .Location = New Point(90, 150)
               .Size = New Size(200, 800)
            End With

            With .Controls
            .Add(button1)
            .Add(button2)
            .Add(button3)
            .Add(button4)
            .Add(text1)
            .Add(text2)
            .Add(text3)
            .Add(DateTimePicker1)
            End With
      End With
   End Sub
      
   Public Shared Sub Main
      Application.Run(new Form1)
   End Sub

   Private Sub SetUp
      ' Create a DataSet with two tables and one relation.
      MakeDataSet
      BindControls
   End Sub

   Private 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 
      ' TableName.ColumnName" string.

      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, AddressOf CurrencyStringToDecimal
      AddHandler b.Format, 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")
   End Sub

   Private Sub DecimalToCurrencyString(sender As Object, cevent As 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".

      ' The application can only convert to string type. 
   
      If cevent.DesiredType IsNot GetType(String) Then
         Exit Sub
      End If 
   
      cevent.Value = CType(cevent.Value, decimal).ToString("c")
   End Sub

   Private Sub CurrencyStringToDecimal(sender As Object, cevent As 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 IsNot GetType(decimal) Then
         Exit Sub
      End If

      cevent.Value = Decimal.Parse(cevent.Value.ToString, _
      NumberStyles.Currency, nothing)
      
      ' 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)
   End Sub

   Private Sub button1_Click(sender As Object, e As System.EventArgs)
      ' Go to the previous item in the Customer list.
      bmCustomers.Position -= 1
   End Sub

   Private Sub button2_Click(sender As Object, e As System.EventArgs)
      ' Go to the next item in the Customer list.
      bmCustomers.Position += 1
   End Sub

   Private Sub button3_Click(sender As Object, e As System.EventArgs)
      ' Go to the previous item in the Order list.
      bmOrders.Position -= 1
   End Sub

   Private Sub button4_Click(sender As Object, e As System.EventArgs)
      ' Go to the next item in the Orders list.
      bmOrders.Position += 1
   End Sub

   ' Creates a DataSet with two tables and populates it.
   Private Sub MakeDataSet
      ' Create a DataSet.
      ds = New DataSet("myDataSet")

      ' Creates two DataTables.
      Dim tCust As DataTable = New DataTable("Customers")
      Dim tOrders As DataTable = New DataTable("Orders")

      ' Create two columns, and add them to the first table.
      Dim cCustID As DataColumn = New DataColumn("CustID", _
      System.Type.GetType("System.Int32"))
      Dim cCustName As DataColumn = New DataColumn("CustName")
      tCust.Columns.Add(cCustID)
      tCust.Columns.Add(cCustName)

      ' Create three columns, and add them to the second table.
      Dim cID As DataColumn = _
         New DataColumn("CustID", System.Type.GetType("System.Int32"))
      Dim cOrderDate As DataColumn = _
         New DataColumn("orderDate", System.Type.GetType("System.DateTime"))
      Dim cOrderAmount As DataColumn = _
         New DataColumn("OrderAmount", System.Type.GetType("System.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.
      Dim dr As DataRelation = New _
         DataRelation("custToOrders", cCustID, cID)
      ds.Relations.Add(dr)
      
      ' Populate the tables. For each customer and orders,
      ' create two DataRow variables.
      Dim newRow1 As DataRow
      Dim newRow2 As DataRow

         ' Create three customers in the Customers Table.
         Dim i As Integer
         For i = 1 to 3
            newRow1 = tCust.NewRow
            newRow1("custID") = i
            ' Adds the row to the Customers table.
            tCust.Rows.Add(newRow1)
         Next

         ' 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.
         Dim j As Integer
         For i = 1 to 3
         For j = 1 to 5
            newRow2 = tOrders.NewRow
            newRow2("CustID") = i
            newRow2("orderDate") = New DateTime(2001, i, j * 2)
            newRow2("OrderAmount") = i * 10 + j * .1
            ' Add the row to the Orders table.
            tOrders.Rows.Add(newRow2)
         Next
         Next
   End Sub
End Class

Observações

Use a Binding classe para criar e manter uma ligação simples entre a propriedade de um controlo e a propriedade de um objeto, ou a propriedade do objeto atual numa lista de objetos.

Como exemplo do primeiro caso, pode-se associar a Text propriedade de um TextBox controlo à FirstName propriedade de um Customer objeto. Como exemplo do segundo caso, pode vincular a Text propriedade de um TextBox controlo à FirstName propriedade de um DataTable que contém clientes.

A Binding classe também permite formatar valores para exibição através do Format evento e recuperar valores formatados através do Parse evento.

Ao construir uma Binding instância com Binding construtor, deve especificar três itens:

• O nome da propriedade de controlo a que se deve ligar.

• A fonte de dados.

• O caminho de navegação que resolve para uma lista ou propriedade na fonte de dados. O caminho de navegação também é usado para criar a propriedade do BindingMemberInfo objeto.

Primeiro, deve especificar o nome da propriedade de controlo à qual pretende vincular os dados. Por exemplo, para mostrar dados num TextBox controlo, especifique a Text propriedade.

Em segundo lugar, pode especificar uma instância de qualquer uma das classes na tabela seguinte como fonte de dados.

Em terceiro lugar, deve especificar o caminho de navegação, que pode ser uma string vazia (""), um único nome de propriedade ou uma hierarquia de nomes delimitada por períodos. Se definir o caminho de navegação para uma cadeia vazia, o ToString método será chamado no objeto fonte de dados subjacente.

Se a fonte de dados for um DataTable, que pode conter múltiplos DataColumn objetos, o caminho de navegação deve ser usado para resolver para uma coluna específica.

É necessário um caminho de navegação delimitado por períodos quando a fonte de dados está definida para um objeto que contém múltiplos DataTable objetos (como um DataSet ou DataViewManager). Também pode usar um caminho de navegação delimitado por períodos quando se atribui a um objeto cujas propriedades retornam referências a outros objetos (como uma classe com propriedades que devolvem outros objetos de classe). Por exemplo, os seguintes caminhos de navegação descrevem todos campos de dados válidos:

• "Tamanho. Altura"

• "Fornecedores.Nome da Empresa"

• "Regions.RegionsParaClientes.NomeCliente"

• "Regions.regionsParaClientes.clientesParaEncomendas.EncomendasParaDetalhes.Quantidade"

Cada membro do caminho pode devolver uma propriedade que resolve para um único valor (como um inteiro), ou uma lista de valores (como um array de cadeias). Embora cada membro no caminho possa ser uma lista ou propriedade, o membro final deve resolver para uma propriedade. Cada membro constrói sobre o membro anterior: "Size.Height" resolve para a Height propriedade para o atual Size; "Regions.regionsToCustomers.CustomerFirstName" resolve para o primeiro nome do cliente atual, onde o cliente é um dos clientes da região atual.

A DataRelation devolve uma lista de valores ligando um DataTable a um segundo DataTable em um DataSet. Se os DataSet objetos contém, DataRelation pode especificar o elemento de dados como um TableName seguido de um RelationName, e depois um ColumnName. Por exemplo, se o DataTable "Suppliers" nomeado contiver um DataRelation "suppliers2products" nomeado, o membro dos dados pode ser "Suppliers.suppliers2products.NomeProduto".

A fonte de dados pode consistir num conjunto de classes relacionadas. Por exemplo, imagine um conjunto de classes que cataloga sistemas solares. A classe nomeada System contém uma propriedade nomeada Stars que devolve uma coleção de Star objetos. Cada Star objeto tem Name propriedades e, Mass bem como uma Planets propriedade que devolve uma coleção de Planet objetos. Neste sistema, cada planeta também tem Mass propriedades de un.Name Cada Planet objeto tem ainda uma Moons propriedade que devolve uma coleção de Moon objetos, cada um dos quais também tem Name propriedades e.Mass Se especificar um System objeto como fonte de dados, pode especificar qualquer um dos seguintes elementos como membro de dados:

• "Stars.Name"

• "Estrelas. Missa"

• "Stars.Planets.Name"

• "Estrelas.Planetas.Massa"

• "Stars.Planets.Moons.Name"

• "Estrelas.Planetas.Luas.Massa"

Os controlos que podem ser simples-limitados apresentam uma coleção de Binding objetos num ControlBindingsCollection, à qual pode aceder através da propriedade do DataBindings controlo. Adiciona-se a Binding à coleção chamando o Add método, ligando assim uma propriedade do controlo a uma propriedade de um objeto (ou a uma propriedade do objeto atual numa lista).

Pode simplesmente ligar a qualquer objeto que derive da classe System.Windows.Forms.Control, por exemplo, os seguintes controlos Windows:

• Button

• CheckBox

• CheckedListBox

• ComboBox

• DateTimePicker

• DomainUpDown

• GroupBox

• HScrollBar

• Label

• LinkLabel

• ListBox

• ListView

• MonthCalendar

• NumericUpDown

• PictureBox

• ProgressBar

• RadioButton

• RichTextBox

• ScrollBar

• StatusBar

• TextBox

• TreeView

• VScrollBar

A BindingManagerBase classe é uma classe abstrata que gere todos os Binding objetos de uma fonte de dados e membro de dados específicos. As classes que derivam de BindingManagerBase são as CurrencyManager e as PropertyManager classes. A forma como a Binding é gerida depende de o Binding ser uma ligação de lista ou uma ligação de propriedade. Por exemplo, se for uma ligação de lista, pode usar o BindingManagerBase para especificar a Position na lista; o Position, portanto, determina qual o item (de todos os itens da lista) que está realmente ligado a um controlo. Para devolver o apropriado BindingManagerBase, use o BindingContext.

Para adicionar uma nova linha a um conjunto de controlos atribuídos ao mesmo DataSource, use o AddNew método da BindingManagerBase classe. Use a Item[] propriedade da BindingContext classe para devolver o .CurrencyManager Para evitar a adição da nova linha, use o CancelCurrentEdit método.

Ver também

• BindingContext
• BindingManagerBase
• ComboBox
• DataGrid