C# Form

Every Windows Forms program will use the Form class. In many programs, the Load, FormClosing and FormClosed event handlers provide needed functionality. We look closer at Form. We demonstrate several event handlers on the Form class.

This C# tutorial shows how to use the Form type in Windows Forms.

Get started

To get started with Form, all you need to do is create a new Windows Forms program. Next, let's add the Load event handler. In Visual Studio, double-click somewhere on the visible Form. In Form1_Load, you can set things like the title text (Text property) or the Window position. This is also a good place to put some initialization code if you need to.

Program that demonstrates Load, FormClosing, FormClosed [C#]

using System;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
	public Form1()
	{
	    InitializeComponent();
	}

	private void Form1_Load(object sender, EventArgs e)
	{
	    // You can set properties in the Load event handler.
	    this.Text = DateTime.Now.DayOfWeek.ToString();
	    this.Top = 60;
	    this.Left = 60;
	}

	private void Form1_FormClosing(object sender, FormClosingEventArgs e)
	{
	    // You can cancel the Form from closing.
	    if ((DateTime.Now.Minute % 2) == 1)
	    {
		this.Text = "Can't close on odd minute";
		e.Cancel = true;
	    }
	}

	private void Form1_FormClosed(object sender, FormClosedEventArgs e)
	{
	    // You can write to a file to store settings here.
	}
    }
}

FormClosing event handler. It's sad to think anyone would ever want to close your program, but this will happen. In FormClosing, you can use logic to see if the program really shouldn't be closed. For example, maybe some data was not saved to the database. Set the Cancel property on the FormClosingEventArgs to true and the Form will remain open. A dialog box might be nice.

FormClosed event handler. In FormClosed, you know for sure the Form has been closed. You can't cancel it now. This is a good place to write settings to the disk or perform some other logic that will affect the state of the system after the Form or entire program terminates.

Type hierarchy

The Form class is the base class for all custom windows (such as Form1) that you might develop. You can reference all these derived types from the base type Form. If you are handling child forms, it is probably best to reference them through the most derived type.

Using new Form

The clearest way to create a new Form is to add the using statement to your code and then call Show or ShowDialog. To start, you can add a button_Click event handler to your button in Windows Forms by double-clicking on it in the Designer. This will create the following method, which we have also added the using statement to.

Method that demonstrates using keyword on Form [C#]

private void button4_Click(object sender, EventArgs e)
{
    using (Form2 form2 = new Form2())
    {
	form2.ShowDialog();
    }
}

Description. This is the Click event handler for button4, which is just a regular Button control in Windows Forms. The two parameters, "object sender" and "EventArgs e" are not specific to this example and you can ignore them.

Using statement. Let's look carefully at how the using statement contains the assignment of a new instance of the Form2 form. The new Form2() constructor is inside the using condition.

ShowDialog method. The ShowDialog method is called on the new instance of the Form. This will show the dialog in the form. You can assign its result to a DialogResult.

System resources

Form types implement the IDisposable interface, which is a special interface that is called when you have the "using" statement. Windows Forms use system resources that must be cleaned up after you are done with them. No matter what happens in ShowDialog, the Form instance will be disposed of.

Argument

Here we see a short example of how you can use DialogResult and ShowDialog together. Additionally, we pass a parameter to the Form3 constructor. It is useful to pass parameters to Form constructors. You will need to modify the constructor manually.

Version that passes argument to Form [C#]

private void button1_Click(object sender, EventArgs e)
{
    using (Form3 form3 = new Form3(new object())) // <-- Parameter
    {
	DialogResult result = form3.ShowDialog();
	if (result == DialogResult.OK) // <-- Checks DialogResult
	{
	}
    }
}

Summary

The Form type presents several important event handlers as well as properties. The Load, FormClosing, and FormClosed event handlers are of particular interest. Most of the properties and other event handlers are not covered here, but can be used in a similar way to those in the example. Custom types that derive from Form can also be used.