Sams Teach Yourself C# in 24 Hours

By James Foxall and Wendy Haro-Chun

• Table of Contents
  • Copyright
  • About the Authors
  • Acknowledgments
  • Tell Us What You Think!
  • Introduction
  • Audience and Organization
  • Conventions Used in This Book
  • Onward and Upward!
  • Part I. The Visual Studio Environment
  • Hour 1. A C# Programming Tour
  • Hour 2. Navigating C#
  • Hour 3. Understanding Objects and Collections
  • Hour 4. Understanding Events
  • Part II. Building a User Interface
  • Hour 5. Building FormsPart I
  • Hour 6. Building FormsPart II
  • Hour 7. Working with the Traditional Controls
    • Displaying Static Text with the Label Control
    • Allowing Users to Enter Text Using a Text Box
    • Creating Buttons
    • Creating Containers and Groups of Option Buttons
    • Displaying a List with the List Box
    • Creating Drop-Down Lists Using the Combo Box
    • Summary
    • Q&A
    • Workshop
  • Hour 8. Advanced Controls
  • Hour 9. Adding Menus and Toolbars to Forms
  • Hour 10. Drawing and Printing
  • Part III. Making Things HappenProgramming!
  • Hour 11. Creating and Calling Methods
  • Hour 12. Using Constants, Data Types, Variables, and Arrays
  • Hour 13. Performing Arithmetic, String Manipulation, and Date/Time Adjustments
  • Hour 14. Making Decisions in C# Code
  • Hour 15. Looping for Efficiency
  • Hour 16. Debugging Your Code
  • Hour 17. Designing Objects Using Classes
  • Hour 18. Interacting with Users
  • Part IV. Working with Data
  • Hour 19. Performing File Operations
  • Hour 20. Controlling Other Applications Using Automation
  • Hour 21. Working with a Database
  • Part V. Deploying Solutions and Beyond
  • Hour 22. Deploying a Solution
  • Hour 23. Introduction to Web Development
  • Hour 24. The 10,000-Foot View
  • Appendix A. Answers to Quizzes/Exercises

Creating Drop-Down Lists Using the Combo Box

List boxes are great, but they have two shortcomings. First, they take up quite a bit of space. Second, users can't enter their own values; they have to select from the items in the list. If you need to conserve space or if you want to allow a user to enter a value that may not exist in the list, use the Combo Box control.

Combo boxes have an Items collection that behaves exactly like that of the List Box control (refer to the previous section for information on manipulating lists). Here I will show you the basics of how a combo box works.

Add a new combo box to the form by double-clicking the ComboBox item in the toolbox. Set the combo box's properties as follows:

The first thing you should note is that the combo box has a Text property, whereas the list box doesn't. This works the same as the Text property of a text box. When the user selects an item from the drop-down list, the value of the selected item is placed in the Text property of the text box. The default behavior of a combo box is to allow the user to enter any text in the text box portion of the control—even if the text doesn't exist in the list. Shortly, I'll show you how to change this behavior.

Select the Items property of the combo box in the Properties window and click the button that appears. Add the following items to the String Collection editor and click OK to commit your entries.

• Black
• Blue
• Gold
• Green
• Red
• Yellow

Press F5 to run the project. Click the arrow at the right side of the combo box and a drop-down list appears (see Figure 7.18).

Figure 7.18 Combo boxes conserve space.

Next, try typing in the text Magenta. C# lets you do this. Indeed, you can type any text that you desire. Often, you'll want to restrict a user to entering only values that appear in the list. To do this, you change the DropDownStyle property of the combo box. Close the form to stop the running project and change the DropDownStyle property of the combo box to DropDownList. Press F5 to run the project again and try to type text into the combo box. You can't. However, if you enter a character that is the start of a list item, C# will select the closest matching entry.

As a matter of fact, clicking in the "text box" portion of the combo box opens the list the same as if you clicked the drop-down arrow. When set as a DropDownList, a combo box won't allow any text entry; therefore, the user is limited to selecting items from the list.

Stop the running project now and save your work. As you can see, the combo box and list box offer similar functionality. In fact, the coding of their lists is identical. However, each one of these controls serves a slightly different purpose. Which one is better? That depends entirely on the situation. As you use professional applications, pay attention to their interfaces; you'll start to get a feel for which control is appropriate in a given situation.

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