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
  • Hour 8. Advanced Controls
  • Hour 9. Adding Menus and Toolbars to Forms
  • Hour 10. Drawing and Printing
    • Understanding the Graphics Object
    • Working with Pens
    • Using System Colors
    • Working with Rectangles
    • Drawing Shapes
    • Drawing Text
    • Persisting Graphics on a Form
    • Build a Graphics Project Example
    • Summary
    • Q&A
    • Workshop
  • 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

Persisting Graphics on a Form

You'll often use the techniques discussed in this hour to draw to a form. However, you may recall from earlier hours that when you draw to a form (actually, you draw to a Graphics object that references a form), the things that you draw aren't persisted; the next time the form paints itself, the drawn elements will disappear. For example, if the user minimizes the form or obscures the form with another window, the next time the form is painted, it will be missing any and all drawn elements that were obscured. You can use a couple of approaches to deal with this behavior:

• Place all code that draws to the form in the form's Paint event.
• Draw to a memory bitmap and copy the contents of the memory bitmap to the form in the form's Paint event.

If you're drawing only a few items, placing the drawing code in the Paint event might be a good approach. However, consider a situation in which you've got a lot of drawing code. Perhaps the graphics are drawn in response to user input, so you can't re-create them all at once. In these situations, the second approach is clearly better.

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