Xcode supports the building of iPhone and Mac OS X applications. When you create a new project in Xcode (which you do by choosing File

Figure B.1. Figure B-1

As you can see, you have two main project types to create (iPhone OS and Mac OS X). Under the iPhone OS category, you have the Application item, which is further divided into two categories: Navigation-based Application and Window-based Application. Clicking the Application item displays all the project types you can create, as follows:

Select the project type you want to create and click the Choose button. You are then asked to name the project.

When the project is created, Xcode displays all the files that make up your project (see Figure B-2).

Figure B.2. Figure B-2

The Xcode window is divided into five sections:

To edit a code file, click the filename of a file to open the editor. Depending on what you click, the appropriate editor is launched. For example, if you click an .h or .m file, the code editor in which you can edit your source code is displayed (see Figure B-3).

Figure B.3. Figure B-3

If you click a .plist file, the XML Property List editor is launched (see Figure B-4).

Figure B.4. Figure B-4

The Xcode window contains the toolbar section, in which you can place your favorite items for quick access. By default, the following items are placed in the toolbar:

You can add items to the toolbar by right-clicking the toolbar and selecting Customize Toolbar. You then see a drop-down pane showing all the items that you can add to the toolbar (see Figure B-5). To add an item to the toolbar, drag the item directly onto the toolbar.

Figure B.5. Figure B-5

One of the most common features of modern IDE is code completion, which makes the IDE automatically try to complete the statement you are typing based on the current context. In Xcode, this code-completion feature is known as Code Sense. As an example, when you type the letters UIA in a method, such as the viewDidLoad() method, Xcode automatically suggests the UIAlertView class (see Figure B-6; notice that the suggested characters are displayed in gray). If you want to accept the suggested word, simply press the Tab or Enter key.

Figure B.6. Figure B-6

Besides getting Xcode to complete the word for you, you can also invoke the Code Sense feature by pressing the Esc key (or press F5). Code Sense displays a list of words matching whatever you have typed (see Figure B-7).

Figure B.7. Figure B-7

As you type in Xcode, Xcode automatically recognizes the code and inserts the relevant parameters" placeholders. For example, if you invoke the methods of an object, Xcode inserts the placeholders of the various parameters. Figure B-8 shows an example of the placeholders inserted for the UIAlertView object after you type ini. To accept the placeholders for the various parameters, press the Tab key.

Figure B.8. Figure B-8

To enter the value for each parameter, press to move to each parameter. Alternatively, click each placeholder and type over it.

To execute an application, you first select the active SDK to use. You also choose whether you want to test it on a real device or use the included iPhone Simulator. You do so by selecting from the Overview list (see Figure B-9).

Figure B.9. Figure B-9

To run the application, press Command-R, and Xcode will build and deploy the application onto the selected device or Simulator.

When you try to run your application, Xcode first tries to build the project before it can deploy the application onto the real device or Simulator. Any syntax errors that Xcode detects are immediately highlighted in red. Figure B-10 shows Xcode highlighting a syntax error. The error with the code block is the missing brace symbol ([) for the [[UIAlertView alloc] statement:

UIAlertView *alert = [UIAlertView alloc]
                             initWithTitle:@"Hello World!"
                             message:@"Hello, my World"
                             delegate:self
                             cancelButtonTitle:@"OK"
                             otherButtonTitles:nil];

Figure B.10. Figure B-10

If you have more than one error, you can also click the error icon to view the list of errors (see Figure B-11).

Figure B.11. Figure B-11

Objective-C is a case-sensitive language, and therefore one of the most common mistakes that beginners make is mixing up the capitalization for some of the method names. Consider the following:

- (void)viewDidLoad {
    UIAlertView *alert = [[UIAlertView alloc]
                             initwithTitle:@"Hello World!"
                             message:@"Hello, my World"
                             delegate:self

cancelButtonTitle:@"OK"
                             otherButtonTitles:nil];
    [alert show];
    [alert release];
    [super viewDidLoad];
}

Can you spot the error? Syntactically, the preceding statements have no problem. However, one of the parameters appears with the wrong capitalization. It turns out that initwithTitle: must be spelled as initWithTitle:. When you compile the program, Xcode will not flag the preceding code as an error; instead, it will issue you with a warning message displayed in yellow (see Figure B-12).

Figure B.12. Figure B-12

When you see a warning message in Xcode, pay special attention to it and check that the method name is spelled correctly, including the capitalization. Failing to do so may result in a runtime exception. Figure B-13 shows the runtime exception message that Xcode displays when a runtime exception occurs.

Figure B.13. Figure B-13

When a runtime exception occurs, the best way to troubleshoot the error is to open the Debugger Console window by pressing Shift-Command-R. The Debugger Console window displays all the debugging information that is printed when Xcode debugs your application. This window usually contains the clue that helps you determine exactly what went wrong behind the scenes. Figure B-14 shows the content of the Debugger Console window when the exception occurs. To find out the cause of the crash, scroll to the bottom of the window and look for the section displayed in bold. In this case, note the reason stated. It is quite obvious that the problem is with the UIAlertView object.

Figure B.14. Figure B-14

Setting breakpoints in your code is a very handy tool to use to debug your application. Breakpoints allow you to execute your code line by line and examine the values of variables so that they perform as expected.

In Xcode, you set a breakpoint by clicking the left column of the code editor (see Figure B-15).

Figure B.15. Figure B-15

After you have set breakpoints in your application, you need to press Command-Y to debug your application so that your breakpoints will be stopped when they are reached.

When the application reaches the breakpoint you have set, Xcode displays the current line of execution with a red arrow (see Figure B-16).

Figure B.16. Figure B-16

At this juncture, you can do several things:

In addition to setting breakpoints to trace the flow of your application, you can use the NSLog() method to print debugging messages to the Debugger Console window. The following NSLog() statement prints a message to the Debugger Console window when the application changes orientation:

- (void)willRotateToInterfaceOrientation:
    (UIInterfaceOrientation) toInterfaceOrientation
    duration: (NSTimeInterval) duration {

    NSLog(@"In the willRotateToInterfaceOrientation: event handler");

    UIInterfaceOrientation destOrientation = toInterfaceOrientation;
    if (destOrientation == UIInterfaceOrientationPortrait)
    {
        btn.frame = CGRectMake(20,20,280,37);
    }
    else
    {
        btn.frame = CGRectMake(180,243,280,37);
    }
}

Figure B-18 shows the output in the Debugger Console window (press Shift-Command-R to display it).

Figure B.18. Figure B-18

During the course of your development, you often need to check on the various methods, classes, and objects used in the iPhone SDK. The best way to check them out is to refer to the documentation. Xcode allows you to quickly and easily browse the definitions of classes, properties, and methods through the use of the Option key. To view the help documentation of an item, simply press the Option key. The cursor changes to a cross-hair. Double-click the item you want to check out, and the Developer Documentation window appears (see Figure B-19).

Figure B.19. Figure B-19

One very useful tool in the Documentation is the Research Assistant (Help

Figure B.20. Figure B-20