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Intro to Windows Forms

Example C# Windows Forms application

A form in Windows Forms programming is a window that contains widgets/controls
A widget or control is a software component that a user manipulates to interact with an application
Form1 represents the application's main window
Select Toolbox from the left side of the screen and drop a Label onto Form1
Change the Text property of the label to Hello, Windows! as shown in the image below:
Ctrl-F5 to run the application

Examine the code by double-clicking on the desired file in the Solution Explorer

Program.cs
```
using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;

namespace HelloWindows
{
    static class Program
    {
        /// 
        /// The main entry point for the application.
        /// 
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}
```
1. This file is rarely edited
2. The using directive is like import in Java: it allows the programmer to use a type in the namespace without having to preface the type with the namespace. Example: System.Windows.Forms.Application vs. Application
3. Main() is always the first method executed
4. Application provides static methods and properties to manage an application, such as methods to start and stop an application, to process Windows messages, and properties to get information about an application
5. Application.Run() begins running a standard application message loop and makes the given Form visible; Run() will not return until Form1 is closed
Form1.cs
```
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace HelloWindows
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
    }
}
```
1. To view the code instead of the form designer, right-click the form and select View Code from the context menu
2. This is the file where you will write the app's main logic
3. Form1 inherits from System.Windows.Forms.Form, a class that represents a window or dialog box
4. Form1 is partial because part of Form1 is defined in another file (Form1.Designer.cs)
5. Form1's constructor calls InitializeComponent() which is defined in Form1.Designer.cs

Form1.Designer.cs

namespace HelloWindows
{
    partial class Form1
    {
        /// 
        /// Required designer variable.
        /// 
        private System.ComponentModel.IContainer components = null;

        /// 
        /// Clean up any resources being used.
        /// 
        /// true if managed resources should be disposed; otherwise, false.
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// 
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// 
        private void InitializeComponent()
        {
            this.label1 = new System.Windows.Forms.Label();
            this.SuspendLayout();
            // 
            // label1
            // 
            this.label1.AutoSize = true;
            this.label1.Location = new System.Drawing.Point(84, 42);
            this.label1.Name = "label1";
            this.label1.Size = new System.Drawing.Size(84, 13);
            this.label1.TabIndex = 0;
            this.label1.Text = "Hello, Windows!";
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(284, 262);
            this.Controls.Add(this.label1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.Label label1;
    }
}

This is an auto-generated file that you should not need to modify (only modify if you really know what you're doing)
Form1 is marked partial because the Form1 class is partially defined here and partially in Form1.cs
All components added the form (e.g., labels, buttons, text boxes, etc.) will be declared in this file (see the declaration of label1 at the end of the file)
InitializeComponent() sets all the components' properties (see the settings for label1 and the form)
#region is a preprocessor directive and with #endregion can be used to create collapsible code
/// used to provide XML comments which VS uses to produce documentation

Event handling
1. Drop a Button onto the form from the Toolbox
2. Double-click on the button to setup a callback or event handler, a function which is called when the user clicks on the button
3. Add code to change label1 to say "You clicked the button!":
```
private void button1_Click(object sender, EventArgs e)
{
	label1.Text = "You clicked the button!";
}
```
4. Ctrl-F5 to run; click the button and observe the label's text change
5. Form1.Designer.cs defines a System.Windows.Forms.Button object that has a Click event. The += operator register's the Click event's callback button1_Click():
```
this.button1.Click += new System.EventHandler(this.button1_Click);
```
6. Multiple controls can share the same event handler
  1. Add another button to the form
  2. Make the second button's Click handler be button1_Click
  3. All event handlers have a sender parameter, which is the object that triggered the event
```
private void button1_Click(object sender, EventArgs e)
{
	// sender is either button1 or button2
	if (btn == button1)
		label1.Text = "You pressed the first button!";
	else
		label1.Text = "You pressed the second button!";
}
```

Debugging
1. Use F5, F10, F11 with breakpoints to examine variables, etc.
2. Use System.Diagnostics.Debug.WriteLine("debug message") to display debug information in Visual Studio's Output pane