Graphical Applications Fundamentals

Overview of GUI Applications

Introduction

Microsoft Visual C# is a programming environment that allows you to create various types of applications. In our lessons, we will create graphical applications, also called Windows applications or Windows Forms applications. 

A Windows application primarily appears as a rectangular object that occupies a portion of the screen. This type of object is under the management of the operating system: Microsoft Windows. Based on the functionality of Microsoft Windows, for an application to become useful, it must be opened. An application must have an entry point. On a C/C++ application, this entry point is a function called main.

On a Win32 application, this entry point is a function called WinMain. The C# language defines this entry point with a class's method named Main, as you should know already from your learning C# (some languages like Pascal or JScript .NET don't explicitly designate an entry point but they make it clear and the operating system knows where it is).

The Main() method of C# can be defined as void or as returning an integer value.

1. Start Microsoft Visual C#
2. To create a new application, on the main menu, click File -> New Project or File -> New -> Project...
3. In the Templates section, click Empty Project
4. In the Name edit box, type Exercise2 and click OK
5. On the main menu, click Project -> Add New Item...
6. In the Templates list, click Code File
7. Change the Name to Starter
    
   
8. Click Add
9. Change the contents of the file as follows:
    

   using System; public class Starter { public static int Main() { return 0; } }

Although you can directly create a graphical application when starting your project, if you had created a console application, you can still easily transform it into a Forms application:

• The most required action consists of changing some characteristics of the project. To take care of this, on the main menu, you can click Project -> ProjectName Properties... and then change the value of the Output Type combo box to Windows Application
• Before or after setting the Output Type to Windows Application, you can create a form 

1. On the main menu, click Project -> Exercise2 Properties...
2. On the left side, make sure Application is selected.
   In the right section, click the arrow of the Output Type combo box and select Windows Application
    
   
3. Save and close the window

Windows Forms is a technique of creating computer applications based on the common language runtime (CLR). It offers a series of objects called Windows Controls or simply, controls. These controls are already created in the .NET Framework through various classes. Application programming consists of taking advantage of these controls and customizing them for a particular application. To exploit these controls and other features of the .NET Framework, there are various types of applications you can create, including graphical applications (Windows Application), web-based applications (ASP.NET Web Application), console applications (Console Application), etc.

The objects used in a Windows application are stored in libraries also called assemblies. As normal libraries, these assemblies have the extension .dll (which stands for dynamic link library). In order to use one of these objects, you must know the name of the assembly in which it is stored. Then you must add a reference to that assembly in your application.

To add a reference to an assembly, on the main menu, you can click Project -> Add Reference... You can also right-click the automatically created References node in Solution Explorer and click Add Reference... Any of these actions would display the Add Reference dialog box from where you can click the reference, click Select and click OK. If you don't see the reference you are looking for, you can locate it on another drive or directory using the Browse button.

There are two broad categories of objects used in a Windows Forms application: the forms and the controls. A form is the most fundamental object used on an application. It is a rectangular object that uses part of the computer desktop to represent an application. A form is based on the Form class that is defined in the System.Windows.Forms namespace created in the System.Windows.Forms.dll assembly. Every GUI application you will create starts with a form. There are various techniques you can use to get a form in your application:

• You can programmatically and manually create a form
• You can inherit a form from the Form class
• You can create a form based on another form that either you or someone else created already, etc.

The primary means of getting a form into an application consists of deriving one from the Form class.

1. To add a reference to the assembly in which the Form class is defined, on the main menu, click Project -> Add Reference...
2. In the Add Reference dialog box, click the .NET tab if necessary and scroll down in the list
3. Click System
4. Press and hold Ctrl
5. Click System.Windows.Forms
    
   
6. Click OK
7. To inherit a form from the Form class, change the file as follows:
    

   using System; using System.Windows.Forms; public class Starter : Form { public static int Main() { return 0; } }

8. Save the file

The form is the object that gives presence to an application. Once you have created the (primary) form of your application, you can get it ready to display on the screen. This is taken care of by the Application class equipped to start an application, process its messages or other related issues, and stop the application.

The Application class provides the overloaded Run() method that can be used to start a program. One of the versions of this method takes a form as argument. This form must be the first, main or primary form of your application; it will be the first to display when the application comes up.

1. To prepare the application for starting, change the Main() method as follows:
    

   using System; using System.Windows.Forms; public class Starter : Form { public static int Main() { // Instantiate an Program object Starter frmMain; // Allocate memory for the object, using the new operator frmMain = new Starter(); // Call the Run() static method of the Application // and pass it the instance of the class to display Application.Run(frmMain); // Everything went alright... We hope return 0; } }

2. Test the application
    
   
3. Close it by clicking its system Close button and return to your programming environment

Besides the windows and functionalities we reviewed earlier, when you work on a project, there are other features that become available.

The Server Explorer is an accessory that allows you to access SQL Server databases without using the physical server and without opening Microsoft SQL Server:

The items of this window display in a tree. To expand a node, you can click its + button. To collapse it, click its - button.

The Solution Explorer is a window that displays the file names and other items used in your project:

The items of this window display in a tree. To expand a node, you can click its + button. To collapse it, click its - button. To explore an item, you can double-click it. The result depends on the item you double-clicked.

The Solution Explorer can be used to create a new class, a new folder, or a reference. To perform any of these operations, you can right-click a folder node such as the name of the project, position the mouse on Add and select the desired operation. You can also perform any of these operations from the Project category of the main menu.

Besides adding new items to the project, you can also use the Solution Explorer to build the project or change its properties. If you add one or more other project(s) to the current one, one of the projects must be set as the default. That project would be the first to come up when the user opens the application. By default, the first project created is set as the default. If you have more than one project, to set the default, right-click the name of the desired project in Solution Explorer and click Set As StartUp Project.

The Solution Explorer also you to rename or delete some of the items that belong to your project.

1. To start a new project, on the main menu, click File -> New -> Project...
2. In the Templates list, click Empty Project and change the Name to Exercise3
3. Click OK
4. On the main menu, click Project -> Exercise3 Properties...
5. In the left frame, make sure Application is selected.
   In the right frame, click the arrow of the Output Type combo box and select Windows Application
6. If the Solution Explorer is not visible, on the main menu, click View -> Solution Explorer.
   In the Solution Explorer, right-click Exercise3 and click Add Windows Form...
7. In the Templates list, make sure Windows Form is selected.
   Set the Name to Exercise and click Add

The Class View displays the various classes used by your project, including their ancestry. The items of the Class View an organized as a tree list with the name of the project on top:

The Class View shares some of its functionality with the Solution Explorer. This means that you can use it to build a project or to add new class.

While the Solution Explorer displays the items that are currently being used by your project, the Class View allows you to explore the classes used in your applications, including their dependencies. For example, sometimes you will be using a control of the of the .NET Framework and you may wonder from what class that control is derived. The Class View, rather than the Solution Explorer, can quickly provide this information. To find it out, expand the class by clicking its + button.

1. If the Class View is not visible, on the main menu, click View -> Class View.
   In the Class View, expand the Exercise2 node if necessary
2. Right-click the name of the project Exercise3 -> Add -> Class...
3. In the Templates list, make sure Class is selected. Change the Name to Central and click Add
4. Change the file as follows:
    

   using System; using System.Windows.Forms; namespace Exercise3 { public class Central { public static int Main() { Application.Run(new Exercise()); return 0; } } }

5. Execute the application to see the new form

On a form, the client area is the body of the form without the title bar, its borders and other sections we have not mentioned yet such as the menu, scroll bars, etc:

Besides the form, every control also has a client area. The role of the client area is to specify the bounding section where the control can be accessed by other controls positioned on it. Based on this, a control can be visible only within the client area of its parent. Not all controls can be parent.

Application programming primarily consists of adding objects to your project. Some of these objects are what the users of your application use to interact with the computer. As the application developer, one of your jobs will consist of selecting the necessary objects, adding them to your application, and then configuring their behavior. There are various ways you can get a control into your application. If you are using Notepad or a text editor to add the objects, you can write code. If you are using Microsoft Visual C#, you can visually select an object and add it.

To create your applications, there are two settings you will be using. If a control is displaying on the screen and you are designing it, this is referred to as design time. This means that you have the ability to manipulate the control. You can visually set the control’s appearance, its location, its size, and other necessary or available characteristics. The design view is usually the most used and the easiest because you can glance at a control, have a realistic display of it and configure its properties. The visual design is the technique that allows you to visually add a control and manipulate its display. This is the most common, the most regularly used, and the easiest technique.

The other technique you will be using to control a window is with code, writing the program. This is done by typing commands or instructions using the keyboard. This is considered, or referred to, as run time. This is the only way you can control an object’s behavior while the user is interacting with the computer and your program.