Developing User Interfaces
CMSC 498B
Spring 2005
Prof. Ben Bederson
Project #4
Due April 21, 2005

Purpose

The purpose of this program is to develop an understanding of building custom widgets and rendering with 2D graphics libraries.

The Problem

You must write a custom widget from scratch (meaning you extend UserControl) that supports editing and selection of multi-line text.  Essentially, you are writing a slightly simplified version of TextBox.  The goal is to create a fully interactive working multi-line word-wrapping text box with selection - but you do not have to worry about data binding, or any public APIs for your control. The requirements for this project are:

• You must do all the rendering "manually", that is with calls to Graphics.DrawString(), Graphics.FillRectangle(), etc.  You must perform all your own input event handling, and you may not use any other Controls.  Specifically, your control may not have any child controls.
• You should use a proportional space font such as Times Roman.
• Your control should support standard text editing with a text cursor, including at least:
  • Regular characters
  • Arrow keys that move the text cursor.  Note that when when the up or down arrow keys are pressed, the cursor must move to the position in the line above or below
  • If you press the up or down arrow keys when the line the cursor will move to is shorter than the current line, then the cursor should go to the end of the new line (as opposed to sitting out in space which would require inserting spaces).
  • Enter key must start a new line
  • Backspace key must delete the character before the text cursor
  • Delete key must delete the character after the text cursor
  • Home key must move the text cursor to the beginning of the current line
  • End key must move the text cursor to the end of the current line
• The text cursor should be rendered as a vertical bar that blinks, and should be put just before the spot where the next character will be entered when a key is pressed.
• Your control should support word wrap that automatically breaks words delimited by spaces.  That is, if you are typing a word and run out of room on the current line, the entire word should be moved to the next line.
• Your control should support resizing.  If the control is resized, the text should be automatically re-word wrapped to fit the new width of the control.
• You do not need to support scrolling, and you do not need to worry about what happens if more text is entered then fits in the control.  If the words just disappear off the bottom, that is fine.
• You have to support keyboard based selection.  Holding down the shift key while pressing any of the 4 arrow keys should result in the appropriate text being rendered as selected (white on black instead of white on black).  I am not going to define the complete semantics here, but the behavior should be identical to the Microsoft TextBox control.
• You have to support mouse-based selection.  Clicking and dragging anywhere in your control should select the text between the click point and the drag point. I am not going to define the complete semantics here, but the behavior should be identical to the Microsoft TextBox control.
• You must define your control in its own Visual Studio project, and then define a separate project with a simple application with one instance of your control to test it.

Hints

• In order to determine how to lay out the text and to determine where to draw selection marks, you need to know exactly how big a string of characters is as rendered.  You can determine this with Graphics.MeasureString().
• Think early about what data structure you will use to store your lines of text.  There are many possible ways that will work, but some data structures will make your life easier than others.  As with all data structure choices, you should consider what the operations you will need to support.  That means you need to read and understand this entire project description.
• Supporting selection is hard.  I strongly suggest that you think about how you are going to implement it before you implement the rest.  If you implement the control without thinking about selection, and then try to add selection later, you might find that you need to change things.
• I suggest you spend some time using the Microsoft TextBox control so you are very familiar with its behavior since you are essentially duplicating it.
• I suggest creating a separate thread to make the cursor blink.  You can use System.Threading.Thread.Sleep() in that thread to sleep for some time, and then when that thread wakes up, it can communicate with the event thread with Control.Invoke() to cause the cursor to appear or disappear.

Submitting

Submit following the same rules as Project #3, but make the subject line of your email contain "DUI: Proj #4 submission".  As before, any submissions after the deadline will be ignored.  If multiple submissions are made, then only the last one before the deadline will be looked at.

The zip file you submit must contain all files within a directory named "proj4-<name>.zip" where you replace <name> with your last name.