Quick Help is an unobtrusive window that provides the documentation for a single symbol. It pops up inline, although you can use Quick Help as a symbol inspector (which stays open) by moving the window after it opens. You can also customize the display in Documentation preferences in Xcode preferences.

To get Quick Help for a symbol, double-click to select the symbol in the Text editor (in this case UIApplicationDelegate; see Figure 3-1) and then choose Help

Figure 3-1. Getting Quick Help.

Headers are a big deal in code because they're the place where you find the class declaration, which includes all of its instance variables and method declarations. To get the header file for a symbol, press

The Documentation window lets you browse and search items that are part of the Apple Developer Connection Reference Library (a collection of developer documentation and tech notes) as well as any third-party documentation you have installed.

You access the documentation by pressing

Figure 3-2. The header file for UIApplicationDelegate.

Figure 3-3. The Documentation window.

Using the Documentation window, you can browse and search the developer documentation — the API references, guides, and article collections about particular tools or technologies — installed on your computer. It's the go-to place for getting documentation about a method or more info about the methods and properties in a framework class.

The Help menu's search field also lets you search Xcode documentation as well as open the Documentation window and Quick Help.

You can also right-click on a symbol and get a pop-up menu that gives you similar options to what you see in the Help menu, including Quick Help (and other related functions).

Xcode can also help you find things in your own project. The submenu that you access by choosing Edit

You'll find that, as your classes get bigger, sometimes you'll want to find a single symbol or all occurrences of a symbol in a file or class. You can easily do that by choosing Edit

Figure 3-4. Finding viewDidLoad in a file.

If you select an item in the top pane of the editor, as you can see in Figure 3-4, the file in which that instance occurs is opened in the bottom pane of the editor and the reference highlighted.

You can also use Find to go through your whole project by choosing Edit

Your searches are saved in your project. Click the triangle next to Find Results in the Groups & Files list to reveal your searches, as shown in Figure 3-6. Select a search to see the search results.

Now that you have some idea of how to use the Xcode Text editor, it's time to write some code.

Figure 3-5. Project Find.

Figure 3-6. Revisiting your searches, which are saved in your project.

As you may recall from Chapter 1 of this minibook, UIApplication loads the parts of the MainWindow.xib to create DeepThoughtsAppDelegate and the window, and sends DeepThoughtsAppDelegate the applicationDidFinishLaunching: message. The applicationDidFinishLaunching: method in DeepThoughtsAppDelegate initializes MainView.

The applicationDidFinishLaunching: message is sent at the very beginning, before the user can even see anything on the screen. Here's where you'd insert your code to initialize your application — where you'd load data, for example, or restore the state of the application to where it was the last time the user exited.

MainViewController is the controller responsible for managing MainView. If you look at the code in MainViewController.m (as shown in Chapter 2 of this minibook), you see the following commented-out code:

/*
 // Implement viewDidLoad to do additional setup after
   loading the view, typically from a nib.
 - (void)viewDidLoad {
[super viewDidLoad];
}
*/

The viewDidLoad message is sent right after the view has been loaded from the nib file — check out Chapter 1 of this minibook for a complete explanation of that loading process. This is the place where you insert your code for view initialization, which in this case means displaying the DeepThoughts' falling words.

The first chunk of code to examine (in bold in Listing 3-2) changes the background color of the Main view and sets up a timer for the interval between each display of falling words or images:

- (void)viewDidLoad {

  [super viewDidLoad];
  self.view.backgroundColor = [UIColor colorWithRed:.5
   green:3 blue:.7 alpha:1];
  [NSTimer scheduledTimerWithTimeInterval:.5 target:self
   selector:@selector(onTimer) userInfo:nil repeats:YES];

  fallingWords = [[NSString alloc] initWithString:@"Peace
   Love Groovy Music"];
  speed = 10.0;
}

The viewDidLoad method enables you to change the background color. A UIColor object represents color and sometimes opacity (alpha value). The colorWithRed:.5 green:3 blue:.7 alpha:1 creates and returns a color object using the specified opacity and RGB component values.

You use the NSTimer class to create timers. A timer waits until a certain time interval has elapsed and then fires, sending a specified message to a target object. I use the scheduledTimerWithTimeInterval:target:selector:userInfo:repeats: class method to create the timer and schedule it on the current run loop in the default mode. The interval is 0.5 seconds, the target is self, and the selector is the message to send to the target when the timer fires — in this case, onTimer. The userInfo is the user info for the timer (set to nil), and the timer is set to repeat — that is, it will repeatedly reschedule itself until invalidated.

An NSString object represents a character string. Representing strings as objects allows you to use strings wherever you use other objects. It also provides the benefits of encapsulation, so that string objects can use whatever encoding and storage are needed for efficiency while simply appearing as arrays of characters. In this case, fallingWords is initialized with the string "Peace Love Groovy Music". The speed is initialized with the value 10.

Connecting the timer to the actual drawing of the display is the onTimer method. Take a good look at the code for this method (from the bold code in Listing 3-2):

- (void)onTimer{

  UILabel *fallingImageView = [[UILabel alloc]
   initWithFrame:CGRectMake(0, 0, 100, 30)];
  fallingImageView.text = fallingWords;
  fallingImageView.textColor = [UIColor purpleColor];
  fallingImageView.font = [UIFont systemFontOfSize:30];
  fallingImageView.backgroundColor = [UIColor
    colorWithRed:.5 green:3 blue:.7 alpha:1];
  fallingImageView.adjustsFontSizeToFitWidth = YES;

  int startX = round(random() % 80);
  int endX = round(random() % 80);
  //speed of falling
  double randomSpeed = (1/round(random() % 100) +1) *speed;
  // image size;
  double scaleH = (1/round(random() % 100) +1) *30;
  double scaleW = (1/round(random() % 100) +1) *200;

  [self.view addSubview:fallingImageView];

  fallingImageView.frame = CGRectMake(startX, −100, scaleW,
   scaleH);

  fallingImageView.alpha = .75;

  [UIView beginAnimations:nil context:fallingImageView];
  [UIView setAnimationDuration:randomSpeed];
  [UIView setAnimationDelegate:self];
       [UIView
   setAnimationDidStopSelector:@selector(
   animationDone:finished:context:)];

  fallingImageView.frame = CGRectMake(endX, 500, scaleW,
   scaleH);

  [UIView commitAnimations];
}

-(void)animationDone:(NSString *)animationID
 finished:(NSNumber *)finished context:(id)context {
UIImageView *fallingImageView = context;
[fallingImageView removeFromSuperview];
[fallingImageView release];
}

The UILabel class implements a read-only text view. You can use this class to draw one or multiple lines of static text. In this case, the block of code uses the initWithFrame method with CGRectMake to create a rectangle, with the x-coordinate and y-coordinate of the rectangle's origin point at (0, 0) and a specified width and height (100, 30).

The code converts the fallingWords string to fallingImageView for display; sets up the text color, font, and background color; and adjusts the font size for the width. The font and textColor properties apply to the entire text string.

The next block of code uses the random function for the starting and ending points (startX and endX), for speed, and for width (scaleW) and height (scaleH) for fallingImageView. The random function uses a non-linear additive-feedback random number generator, with a default table of size 31 long integers, and returns successive pseudo-random numbers in the range from 0 to 2,147,483,647. Then, addSubview adds a view so that it's displayed above its siblings, and frame specifies the rectangle in the super-layer's coordinate space, using startX, −100, scaleW, and scaleH.

The UIView class provides common methods you use to create all types of views. In this particular code, it's used for a block of animation. The beginAnimations:context: method starts the animation block, and the commitAnimations method ends the block. Inside the block, the code sets property values to make visual changes that comprise the animation. In this case, the code changes the rectangle's starting coordinates from startX to endX, and from −100 to 500:

fallingImageView.frame = CGRectMake(endX, 500, scaleW,
   scaleH);

The setAnimationDuration method sets the animation duration, and setAnimationDidStopSelector sets the message to send to the animation delegate when animation stops. The animation delegate is animationDone, uses removeFromSuperview (an instance method of the UIView class) to remove fallingImageView from its superview, its window, and from the responder chain; and then uses release (an instance method of the NSAutoreleasePool class) to release fallingImageView. Remember, you own any object you create with alloc, which means you're responsible for releasing it when you're done.