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Creating a Cocoa AppController Class

Volume Number: 21 (2005)
Issue Number: 1
Column Tag: Programming

Getting Started

by Dave Mark

Creating a Cocoa AppController Class

In our last Cocoa column, we downloaded the latest and greatest version of Xcode. We created a Foundation Tool, which is an Objective-C program with a console-based interface.

This month, we're going to build a Cocoa app with an interface we designed using Interface Builder. The app will use Cocoa's NSSpeechSynthesizer class to speak a line of text. We'll add a pushbutton to start the speech and another to halt it, even in mid-sentence. The example comes from Chapter 4 of Aaron Hillegass' book, Cocoa Programming for Mac OS X. We'll start by taking a look at a class diagramming approach Aaron uses throughout the book.

A Diagram Speaks a Thousand Words

Before we actually start the process of building our project, take a look at the object diagram shown in Figure 1. This diagramming convention was developed by Aaron Hillegas and I find it works quite well at describing the interrelationships between the classes, objects, methods, and instance variables that come together to make your program work.

The class at the heart of this example is the AppController class. Note that this class features two methods: sayIt: and stopIt:. In Hillegas' drawings, each box represents a class and each arrow connecting two boxes represents the control-dragging connection you create in Interface Builder. For example, in Figure 1, note that 4 of the 5 classes are Cocoa classes (they start with NS). All of our code will be built into a new class that we create called AppController. We'll create two instances of NSButton, one labeled Say it and one labeled Stop. Each of the buttons will target one of the two AppController methods. When we build the project in Interface Builder, we'll create an instance of AppController, then control-drag from each button to the AppController instance and double-click on the method we want called to finish the connection.

We'll also add instance variables to AppController to keep track of the NSTextField (so we can retrieve the text to say it) and the NSSpeechSynthesizer (so we can send it the text to start speaking and send it a stop message to halt the speaking).

Figure 1. An object diagram for the first incarnation of our SpeakLine program.

Create the SpeakLine Project

Launch Xcode and create a new project using the Cocoa Application template. Name the project SpeakLine.

Editing the .nib File

In your SpeakLine project file, in the Groups & Files pane, find the file MainMenu.nib and double-click it to launch Interface Builder. You can find the file in the NIB Files group as well as under the SpeakLine group, in the Resources subgroup.

Once Interface Builder launches, click on the third icon from the left in the palette window, then drag an NSTextField from the palette onto the main window. As you can see in Figure 2, the NSTextField is in the upper-left corner of the set of text items.

Figure 2. Dragging out an NSTextField.

Drag the NSTextField so it is almost as wide as the window (so the dashed blue line appears when you get about a scrollbar's width from the right side of the window). Double-click on the text field and change its text to read Peter Piper picked a peck of pickled peppers or, if you are by yourself, perhaps something a bit more spicy.

Next, click on the second icon from the left at the top of the palette window to show the control palette items. Drag two buttons onto the window, below the NSTextField, with the proper spacing between them and the right side of the window. Label the right button Say It and the left button Stop (double-click on a button to edit its label).

Finally, resize the window itself, making it as short as possible. Figure 3 shows my Interface Builder session. In this picture, I am dragging the Stop button into place. You can see the dashed blue lines showing that the two buttons are aligned with each other and that the Stop button is the correct distance from the text field above it and the Say It button to its right.

Figure 3. Use the blue dashed lines to line up your buttons and NSTextField.

Create the AppController Class

Now that your interface is laid out, it's time to create the new AppController class.

Click on the MainMenu.nib window and click on the Classes tab. Scroll all the way to the left and click on the NSObject class. With NSObject highlighted, select Subclass NSObject from the Classes menu. Name the new subclass AppController (see Figure 4).

Figure 4. Click on the NSObject class and select Subclass NSObject from the Classes menu.

Now you'll add two actions (one for each button) and an outlet (an instance variable that points to the text field) to AppController. Open the Info window by selecting Show Info from the Tools menu. Click on the AppController class in the classes tab in the MainMenu.nib window, then click on the Info window and select Attributes from the popup near the top of the Info window.

Click on the Actions tab, then click on the Add button at the bottom right of the Info window. When the new action appears, name it sayIt:, then click Add and name the second action stopIt: (see Figure 5).

Figure 5. The Info window, showing the AppController class attributes.

Next, click on the Outlet tab and click Add to add an outlet named textField to AppController. Click in the Type column and select NSTextField to set the textField type to NSTextField instead of the generic id.

If you look back at Figure 1, you'll see that we've addressed 3 of the 4 arrows in the object diagram. We'll add the missing outlet, speechSynth, in code in just a minute.

Be sure that the AppController class is selected in the Classes tab and select Create Files for AppController from the Classes menu. This will generate two source files (AppController.m and AppController.h) in your Xcode project which we'll edit in a bit.

Next, create an instance of the AppController class by selecting Instantiate AppController from the Classes menu. Interface Builder will switch the MainMenu.nib window to the Instances tab and a new, blue cube will appear with the name AppController.

As you can see in Figure 6, the AppController instance is represented by a blue cube. The tiny exclamation point in a circle to the lower right of the blue cube tells you that there is at least one unconnected outlet. Let's take care of that now.

Figure 6. The new instance of AppController with an unconnected outlet.

Making Connections

Before you start making your connections, take a quick peek back at Figure 1. There are four connections that need to be made. Three of them will be made by control-dragging. The fourth (speechSynth) will be made in code.

First, we'll connect AppController's textField outlet so it points to the NSTextField in the main window. Make sure the Info window is open before you start your drag.

Control-drag from the AppController blue cube to the text field in the main window. When you release the mouse button, the Info window should display its Connections pane and list the textField outlet. Either double-click on the textField line or make sure it is selected and click the Connect button in the lower-right corner of the Info window (Figure 7).

Figure 7. Click the Connect button to connect the AppController to the textField.

Next, we'll connect the two buttons to their respective AppController methods. Control-drag from the Say It button to the AppController cube then, in the Info window, connect to the sayIt: method.

Now control-drag from the Stop button to the AppController cube and connect to the stopIt: method.

NSWindow's initialFirstResponder

The last bit of Interface Builder work we'll do is to set the NSWindow initialFirstResponder outlet to point to the text field. This tells the window that you want the text field to be active when the window appears so you don't have to click in the text field to start typing. To get a feel for this, try running the program with the initialFirstResponder connected and then with it disconnected to see what happens.

Control-drag from the Window icon (to the left of the blue AppController cube) to the text field. In the Info window, click on the initialFirstResponder outlet and click the Connect button.

Now let's type in the code!

Enter the AppController Code

Head back over to Xcode and edit the AppController.h file. We'll add the declaration of speechSynth:

#import <Cocoa/Cocoa.h>

@interface AppController : NSObject 
	IBOutlet NSTextField *textField;
	NSSpeechSynthesizer *speechSynth;

- (IBAction)sayIt:(id)sender;
- (IBAction)stopIt:(id)sender; 

Next, edit AppController.m to look like this:

#import "AppController.h"
@implementation AppController

- (id)init 
	[super init];
 	NSLog( @"init" );
 	speechSynth = [[NSSpeechSynthesizer alloc] initWithVoice:nil];
	return self; 

- (IBAction)sayIt:(id)sender 
	NSString *string = [textField stringValue];
 if ( [string length] == 0) {   

 [speechSynth startSpeakingString:  string];

 	NSLog( @"Have started to say: %@", string ); 

- (IBAction)stopIt:(id)sender 
	NSLog( @"stopping" );
	[speechSynth stopSpeaking]; 

- (void)dealloc 
	NSLog( @"dealloc" );
	[speechSynth release];
	[super dealloc];

Build and run the application. Notice that you can click the Stop button to stop the speaking, even in the middle.

Take a look through the code. Most of it should make sense, especially if you've been following along with my previous Cocoa columns.

The init: method calls the superclasses' init drops a message to the console, creates an instance of the NSSpeechSynthesizer, then returns a pointer to itself.

sayIt: sends a stringValue message to textField to retrieve the text, then, if there's at least one character in the field, send it via a startSpeakingString message to speechSynth. The string is sent to the console as well, just to help you follow along.

stopIt: sends a message to the console, then sends a stopSpeaking message to speechSynth.

dealloc: is called when the AppController object is released. You'll likely never see the console message, since the AppController object was created automatically and is never sent a release message. When it is loaded from the .nib file, the AppController instance has a ref count of one. Not a big deal, but worth noting.

Till Next Month...

One thing that Aaron does in his book is add a color well to the program so the user can choose their own text color. See if you can do this on your own. You'll want to take advantage of the NSColorWell class.

Be sure to check out and I'll see you next month...

Dave Mark is a long-time Mac developer and author and has written a number of books on Macintosh development, including Learn C on the Macintosh, Learn C++ on the Macintosh, and The Macintosh Programming Primer series. Dave's been busy lately cooking up his next concoction. Want a peek?


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