Cenni preliminari sull'utilizzo di controlli in Windows Form
In questo argomento verranno descritti gli elementi essenziali di un'applicazione Windows Form e verrà illustrato un semplice esempio in cui vengono utilizzati controlli e gestiti eventi in un'applicazione Windows Form.
Applicazioni Windows Form semplici
Un'applicazione Windows Form presenta almeno i seguenti elementi:
Una o più classi che derivano da System.Windows.Forms.Form.
Un metodo Main che richiama il metodo static (shared in Visual Basic) Run passando un'istanza di Form. Il metodo Run elabora i messaggi inviati dal sistema operativo all'applicazione.
Nell'esempio di codice che segue vengono illustrati gli elementi essenziali di un'applicazione Windows Form.
Option Explicit
Option Strict
Imports System
Imports System.Windows.Forms
Public Class MyForm
Inherits Form
Public Sub New()
Me.Text = "Hello World"
End Sub 'New
<STAThread()> _
Public Shared Sub Main()
Dim aform As New MyForm()
' The Application.Run method processes messages from the operating system
' to your application. If you comment out the next line of code,
' your application will compile and execute, but because it is not in the
' message loop, it will exit after an instance of the form is created.
Application.Run(aform)
End Sub
End Class
using System;
using System.Windows.Forms;
public class MyForm : Form {
public MyForm() {
this.Text = "Hello World";
}
[STAThread]
public static void Main(string[] args) {
MyForm aform = new MyForm();
// The Application.Run method processes messages from the operating system
// to your application. If you comment out the next line of code,
// your application will compile and execute, but because it is not in the // message loop, it will exit after an instance of the form is created.
Application.Run(aform);
}
}
Utilizzo di controlli in un'applicazione Windows Form
Nell'esempio di codice che segue viene mostrata un'applicazione semplice per illustrare le modalità con cui le applicazioni Windows Form utilizzano i controlli e gestiscono gli eventi. L'esempio consiste in tre pulsanti su un form; quando si fa clic su uno di essi viene modificato il colore di sfondo.
Option Explicit
Option Strict
Imports System
Imports System.ComponentModel
Imports System.Windows.Forms
Imports System.Resources
Imports System.Drawing
Public Class MyForm
Inherits Form
Private red As Button
Private blue As Button
Private green As Button
Public Sub New()
InitializeComponent()
End Sub
Protected Overloads Overrides Sub Dispose(disposing as Boolean)
MyBase.Dispose(disposing)
End Sub
' InitializeComponent is a helper method for the constructor.
' It is included for consistency with code that is
' auto-generated by the Windows Forms designer in Visual Studio.
Private Sub InitializeComponent()
' Creates three buttons, sets their properties, and attaches
' an event handler to each button.
red = New Button()
red.Text = "Red"
red.Location = New Point(100, 50)
red.Size = New Size(50, 50)
AddHandler red.Click, AddressOf button_Click
Controls.Add(red)
blue = New Button()
blue.Text = "Blue"
blue.Location = New Point(100, 100)
blue.Size = New Size(50, 50)
AddHandler blue.Click, AddressOf button_Click
Controls.Add(blue)
green = New Button()
green.Text = "Green"
green.Location = New Point(100, 150)
green.Size = New Size(50, 50)
AddHandler green.Click, AddressOf button_Click
Controls.Add(green)
End Sub
' Event handler.
Private Sub button_Click(sender As Object, e As EventArgs)
If sender Is red Then
Me.BackColor = Color.Red
Else
If sender Is blue Then
Me.BackColor = Color.Blue
Else
Me.BackColor = Color.Green
End If
End If
End Sub
' The STAThreadAttribute informs the common language runtime that
' Windows Forms uses the single-threaded apartment model.
<STAThread()> _
Public Shared Sub Main()
Application.Run(New MyForm())
End Sub
End Class
using System;
using System.ComponentModel;
using System.Windows.Forms;
using System.Resources;
using System.Drawing;
public class MyForm : Form {
private Button red;
private Button blue;
private Button green;
public MyForm() : base() {
InitializeComponent();
}
protected override void Dispose(bool disposing) {
base.Dispose(disposing);
}
// InitializeComponent is a helper method for the constructor.
// It is included for consistency with code that is
// auto-generated by the Windows Forms designer in Visual Studio.
private void InitializeComponent() {
// A delegate for the click event of a button. The argument to
// the constructor contains a reference to the method that performs the
// event handling logic.
EventHandler handler = new EventHandler(button_Click);
// Creates three buttons, sets their properties, and attaches
// an event handler to each button.
red = new Button();
red.Text = "Red";
red.Location = new Point(100, 50);
red.Size = new Size(50, 50);
red.Click +=handler;
Controls.Add(red);
blue = new Button();
blue.Text = "Blue";
blue.Location = new Point(100, 100);
blue.Size = new Size(50, 50);
blue.Click += handler;
Controls.Add(blue);
green = new Button();
green.Text = "Green";
green.Location = new Point(100, 150);
green.Size = new Size(50, 50);
green.Click += handler;
Controls.Add(green);
}
// Event handler.
private void button_Click(object sender, EventArgs e) {
if (sender == red) this.BackColor = Color.Red ;
else if (sender == blue) this.BackColor = Color.Blue;
else this.BackColor = Color.Green;
}
// The STAThreadAttribute informs the common language runtime that
// Windows Forms uses the single-threaded apartment model.
[STAThread]
public static void Main(string[] args) {
Application.Run(new MyForm());
}
}
Vedere anche
Concetti
Nozioni fondamentali sullo sviluppo di controlli Windows Form
Altre risorse
Sviluppo di controlli Windows Form personalizzati con .NET Framework