Procedura: associare un controllo Windows Form a un oggetto Factory
Quando si compilano controlli che interagiscono con i dati, è a volte necessario associare un controllo a un oggetto o metodo che genera altri oggetti. Tale oggetto o metodo è definito Factory. L'origine dati, ad esempio, potrebbe essere il valore restituito da una chiamata al metodo anziché un oggetto in memoria o un tipo. È possibile associare un controllo a tale tipo di origine dati purché l'origine restituisca un insieme.
È possibile associare facilmente un controllo a un oggetto Factory utilizzando il controllo BindingSource.
Esempio
Nell'esempio riportato di seguito viene dimostrato come associare un controllo DataGridView a un metodo Factory mediante un controllo BindingSource. Il metodo Factory, denominato GetOrdersByCustomerId, restituisce tutti gli ordini di un dato cliente nel database Northwind.
Imports System
Imports System.Collections
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Data.Common
Imports System.Diagnostics
Imports System.Drawing
Imports System.Data.SqlClient
Imports System.Windows.Forms
' This form demonstrates using a BindingSource to bind to a factory
' object.
Public Class Form1
Inherits System.Windows.Forms.Form
' This is the TextBox for entering CustomerID values.
Private WithEvents customerIdTextBox As New TextBox()
' This is the DataGridView that displays orders for the
' specified customer.
Private customersDataGridView As New DataGridView()
' This is the BindingSource for binding the database query
' result set to the DataGridView.
Private ordersBindingSource As New BindingSource()
Public Sub New()
' Set up the CustomerID TextBox.
Me.customerIdTextBox.Location = New Point(100, 200)
Me.customerIdTextBox.Size = New Size(500, 30)
Me.customerIdTextBox.Text = _
"Enter a valid Northwind CustomerID, for example: ALFKI," & _
" then RETURN or click outside the TextBox"
Me.Controls.Add(Me.customerIdTextBox)
' Set up the DataGridView.
customersDataGridView.Dock = DockStyle.Top
Me.Controls.Add(customersDataGridView)
' Set up the form.
Me.Size = New Size(800, 500)
End Sub
' This event handler binds the BindingSource to the DataGridView
' control's DataSource property.
Private Sub Form1_Load(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Me.Load
' Attach the BindingSource to the DataGridView.
Me.customersDataGridView.DataSource = Me.ordersBindingSource
End Sub
' This is a static factory method. It queries the Northwind
' database for the orders belonging to the specified
' customer and returns an IEnumerable.
Public Shared Function GetOrdersByCustomerId(ByVal id As String) _
As IEnumerable
' Open a connection to the database.
Dim connectString As String = "Integrated Security=SSPI;" & _
"Persist Security Info=False;Initial Catalog=Northwind;" & _
"Data Source= localhost"
Dim connection As New SqlConnection()
connection.ConnectionString = connectString
connection.Open()
' Execute the query.
Dim queryString As String = _
String.Format("Select * From Orders where CustomerID = '{0}'", id)
Dim command As New SqlCommand(queryString, connection)
Dim reader As SqlDataReader = _
command.ExecuteReader(CommandBehavior.CloseConnection)
Return reader
End Function
' These event handlers are called when the user tabs or clicks
' out of the customerIdTextBox or hits the return key.
' The database is then queried with the CustomerID
' in the customerIdTextBox.Text property.
Private Sub customerIdTextBox_Leave(ByVal sender As Object, _
ByVal e As EventArgs) Handles customerIdTextBox.Leave
' Attach the data source to the BindingSource control.
Me.ordersBindingSource.DataSource = _
GetOrdersByCustomerId(Me.customerIdTextBox.Text)
End Sub
Private Sub customerIdTextBox_KeyDown(ByVal sender As Object, _
ByVal e As KeyEventArgs) Handles customerIdTextBox.KeyDown
If e.KeyCode = Keys.Return Then
' Attach the data source to the BindingSource control.
Me.ordersBindingSource.DataSource = _
GetOrdersByCustomerId(Me.customerIdTextBox.Text)
End If
End Sub
<STAThread()> _
Shared Sub Main()
Application.EnableVisualStyles()
Application.Run(New Form1())
End Sub
End Class
using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.Common;
using System.Diagnostics;
using System.Drawing;
using System.Data.SqlClient;
using System.Windows.Forms;
// This form demonstrates using a BindingSource to bind to a factory
// object.
public class Form1 : System.Windows.Forms.Form
{
// This is the TextBox for entering CustomerID values.
private TextBox customerIdTextBox = new TextBox();
// This is the DataGridView that displays orders for the
// specified customer.
private DataGridView customersDataGridView = new DataGridView();
// This is the BindingSource for binding the database query
// result set to the DataGridView.
private BindingSource ordersBindingSource = new BindingSource();
public Form1()
{
// Set up the CustomerID TextBox.
this.customerIdTextBox.Location = new Point(100, 200);
this.customerIdTextBox.Size = new Size(500, 30);
this.customerIdTextBox.Text =
"Enter a valid Northwind CustomerID, for example: ALFKI," +
" then RETURN or click outside the TextBox";
this.customerIdTextBox.Leave +=
new EventHandler(customerIdTextBox_Leave);
this.customerIdTextBox.KeyDown +=
new KeyEventHandler(customerIdTextBox_KeyDown);
this.Controls.Add(this.customerIdTextBox);
// Set up the DataGridView.
customersDataGridView.Dock = DockStyle.Top;
this.Controls.Add(customersDataGridView);
// Set up the form.
this.Size = new Size(800, 500);
this.Load += new EventHandler(Form1_Load);
}
// This event handler binds the BindingSource to the DataGridView
// control's DataSource property.
private void Form1_Load(
System.Object sender,
System.EventArgs e)
{
// Attach the BindingSource to the DataGridView.
this.customersDataGridView.DataSource =
this.ordersBindingSource;
}
// This is a static factory method. It queries the Northwind
// database for the orders belonging to the specified
// customer and returns an IEnumerable.
public static IEnumerable GetOrdersByCustomerId(string id)
{
// Open a connection to the database.
string connectString = "Integrated Security=SSPI;" +
"Persist Security Info=False;Initial Catalog=Northwind;" +
"Data Source= localhost";
SqlConnection connection = new SqlConnection();
connection.ConnectionString = connectString;
connection.Open();
// Execute the query.
string queryString =
String.Format("Select * From Orders where CustomerID = '{0}'",
id);
SqlCommand command = new SqlCommand(queryString, connection);
SqlDataReader reader =
command.ExecuteReader(CommandBehavior.CloseConnection);
return reader;
}
// These event handlers are called when the user tabs or clicks
// out of the customerIdTextBox or hits the return key.
// The database is then queried with the CustomerID
// in the customerIdTextBox.Text property.
void customerIdTextBox_Leave(object sender, EventArgs e)
{
// Attach the data source to the BindingSource control.
this.ordersBindingSource.DataSource =
GetOrdersByCustomerId(this.customerIdTextBox.Text);
}
void customerIdTextBox_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Return)
{
// Attach the data source to the BindingSource control.
this.ordersBindingSource.DataSource =
GetOrdersByCustomerId(this.customerIdTextBox.Text);
}
}
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.Run(new Form1());
}
}
#using <System.dll>
#using <System.Data.dll>
#using <System.Drawing.dll>
#using <System.EnterpriseServices.dll>
#using <System.Transactions.dll>
#using <System.Windows.Forms.dll>
#using <System.Xml.dll>
using namespace System;
using namespace System::Collections;
using namespace System::Collections::Generic;
using namespace System::ComponentModel;
using namespace System::Data;
using namespace System::Data::Common;
using namespace System::Data::SqlClient;
using namespace System::Diagnostics;
using namespace System::Drawing;
using namespace System::Windows::Forms;
// This form demonstrates using a BindingSource to bind to a factory
// object.
public ref class Form1: public System::Windows::Forms::Form
{
private:
// This is the TextBox for entering CustomerID values.
static TextBox^ customerIdTextBox = gcnew TextBox;
// This is the DataGridView that displays orders for the
// specified customer.
static DataGridView^ customersDataGridView = gcnew DataGridView;
// This is the BindingSource for binding the database query
// result set to the DataGridView.
static BindingSource^ ordersBindingSource = gcnew BindingSource;
public:
Form1()
{
// Set up the CustomerID TextBox.
this->customerIdTextBox->Dock = DockStyle::Bottom;
this->customerIdTextBox->Text =
L"Enter a valid Northwind CustomerID, for example: ALFKI,"
L" then TAB or click outside the TextBox";
this->customerIdTextBox->Leave += gcnew EventHandler(
this, &Form1::customerIdTextBox_Leave );
this->Controls->Add( this->customerIdTextBox );
// Set up the DataGridView.
customersDataGridView->Dock = DockStyle::Top;
this->Controls->Add( customersDataGridView );
// Set up the form.
this->Size = System::Drawing::Size( 800, 800 );
this->Load += gcnew EventHandler( this, &Form1::Form1_Load );
}
private:
// This event handler binds the BindingSource to the DataGridView
// control's DataSource property.
void Form1_Load(
System::Object^ /*sender*/,
System::EventArgs^ /*e*/ )
{
// Attach the BindingSource to the DataGridView.
this->customersDataGridView->DataSource =
this->ordersBindingSource;
}
public:
// This is a static factory method. It queries the Northwind
// database for the orders belonging to the specified
// customer and returns an IList.
static System::Collections::IList^ GetOrdersByCustomerId( String^ id )
{
// Open a connection to the database.
String^ connectString = L"Integrated Security=SSPI;"
L"Persist Security Info=False;Initial Catalog=Northwind;"
L"Data Source= localhost";
SqlConnection^ connection = gcnew SqlConnection;
connection->ConnectionString = connectString;
connection->Open();
// Execute the query.
String^ queryString = String::Format(
L"Select * From Orders where CustomerID = '{0}'", id );
SqlCommand^ command = gcnew SqlCommand( queryString,connection );
SqlDataReader^ reader = command->ExecuteReader(
CommandBehavior::CloseConnection );
// Build an IList from the result set.
List< DbDataRecord^ >^ list = gcnew List< DbDataRecord^ >;
System::Collections::IEnumerator^ e = reader->GetEnumerator();
while ( e->MoveNext() )
{
list->Add( dynamic_cast<DbDataRecord^>(e->Current) );
}
return list;
}
// This event handler is called when the user tabs or clicks
// out of the customerIdTextBox. The database is then queried
// with the CustomerID in the customerIdTextBox.Text property.
private:
void customerIdTextBox_Leave( Object^ /*sender*/, EventArgs^ /*e*/ )
{
// Attach the data source to the BindingSource control.
this->ordersBindingSource->DataSource = GetOrdersByCustomerId(
this->customerIdTextBox->Text );
}
public:
[STAThread]
static void main()
{
Application::EnableVisualStyles();
Application::Run( gcnew Form1 );
}
};
Compilazione del codice
Per questo esempio sono necessari i seguenti requisiti:
- Riferimenti agli assembly System, System.Data, System.Drawing e System.Windows.Forms.
Per informazioni sulla compilazione di questo esempio dalla riga di comando per Visual Basic o Visual C#, vedere Building from the Command Line (Visual Basic) o Compilazione dalla riga di comando con csc.exe. È anche possibile compilare questo esempio in Visual Studio incollando il codice in un nuovo progetto. Per ulteriori informazioni, vedere Procedura: compilare ed eseguire un esempio di codice Windows Form completo tramite Visual Studio e Procedura: compilare ed eseguire un esempio di codice Windows Form completo tramite Visual Studio e Procedura: compilare ed eseguire un esempio di codice Windows Form completo tramite Visual Studio e Procedura: compilare ed eseguire un esempio di codice Windows Form completo tramite Visual Studio e Procedura: compilare ed eseguire un esempio di codice Windows Form completo tramite Visual Studio.
Vedere anche
Attività
Procedura: associare un controllo Windows Form a un tipo