Create a new Foundation Tool in Project Builder (File → New Project → Tool → Foundation Tool) named “keyvaluecoding”, and save it in your ~/LearningCocoa folder.

Create a new Objective-C class named FoodItem (File → New File → Cocoa → Objective-C Class), as shown in Figure 9-1. Be sure to create both the .h and .m files.

Figure 9-1. Creating the FoodItem class

Edit the FoodItem.h file as follows:

#import <Foundation/Foundation.h>

@interface FoodItem : NSObject {
    NSString * name;                                              // a
                            NSNumber * price;                                             // b
}

- (NSString *)name;                                               // c
                        - (void)setName:(NSString *)aName;                                // d

                        - (NSNumber *)price;                                              // e
                        - (void)setPrice:(NSNumber *)aPrice;                              // f

@end

This code adds the following things:

Edit the FoodItem.m file as follows:

#import "FoodItem.h"

@implementation FoodItem

- (id)init                                                         // a
                        {
                            [super init];
                            [self setName:@"New Item"];
                            [self setPrice:[NSNumber numberWithFloat:0.0]];
                            return self;
                        }

                        - (NSString *)name                                                 // b
                        {
                            return name;
                        }

                        - (void)setName:(NSString *)newName                                // c
                        {
                            [newName retain];
                            [name release]
                            name = newName;
                        }

                        - (NSNumber *)price                                                // d
                        {
                            return price;
                        }

                        - (void)setPrice:(NSNumber *)newPrice                              // e
                        {
                            [newPrice retain];
                            [price release];
                            price = newPrice;
                        }

@end

The code we added performs the following tasks:

Edit the main.m file (located in the Sources folder in Project Builder’s left pane) as follows:

#import <Foundation/Foundation.h>
#import "FoodItem.h"

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    FoodItem * candyBar = [[FoodItem alloc] init];

                            [candyBar takeValue:@"Aero" forKey:@"name"];
                 // a
                            [candyBar takeValue:[NSNumber numberWithFloat:1.25] forKey:@"price"]; // b

                            NSLog(@"item name: %@", [candyBar valueForKey:@"name"]);              // c
                            NSLog(@"    price: %@", [candyBar valueForKey:@"price"]);             // d
                            [candyBar release];                                                   // e
    
    [pool release];
    return 0;
}

The code that we added performs the following tasks:

Save the project (

-S), and then build and run the application (Build → Build and Run, or

-R).

Title the main window “Menu” in the Window Title field of the Info window (Tools → Show Info, or Shift-

-I).

Drag a table view object (NSTableView) from the Cocoa-Data views palette, as shown in Figure 9-4.

Figure 9-4. Adding a table view object to the interface

Resize the table view to fill the window.

Change the Autosizing attributes so that the table view will always occupy the entire window, as shown in Figure 9-5.

Make the width of the columns equal. Select the leftmost column (you may have to double-click), hold the cursor over the right edge of the column so that it turns into a pair of horizontally opposed arrows, then drag the column edge so the column view is divided in half.

Double-click on the header bar for the left column and type Item Name, then press Tab to move to the header bar for the right column.

Type Price as the header for the right column, then press Tab to select the left column.

Edit the Identifier field for the left column in the Attributes pane of the Info panel so it reads name, as shown in Figure 9-6.

Figure 9-6. Editing the identifier attribute of a table column

Repeat for the right column, assigning it an Identifier of price.

Create a subclass of NSObject, and name it MyDataSource.

Instantiate the MyDataSource class (Classes → Instantiate MyDataSource).

Draw a connection from the table view object to the MyDataSource object in the Instances window. Make sure that you have selected the table view, not its surrounding scroll view before you draw the connection. The table view will turn a darker shade of gray when selected.

Select the dataSource outlet in the Connections pane of the Info window, as shown in Figure 9-7, and click the Connect button.

Figure 9-7. Connecting the table view to MyDataSource

Click on MyDataSource in the Classes tab of the MainMenu.nib window, and create the interface files (Classes → Create Files for MyDataSource).

Save (

-S) the nib, and return to Project Builder.

Add the files for the FoodItem class to the project. Using the Finder, locate the FoodItem.h and FoodItem.m files (in the ~/LearningCocoa/Key View Coding directory), and drag them into the Other Sources folder of the Groups & Files panel in Project Builder. When the sheet appears to confirm your copy, ensure that the “Copy items” checkbox is selected, and then click the Add button, as shown in Figure 9-8.

Figure 9-8. Adding our FoodItem class files to the Menu Project

Open the MyDataSource.h file, and edit it to match the following code:

#import <Cocoa/Cocoa.h>

@interface MyDataSource : NSObject
{
    NSMutableArray * items;
}

@end

The code we added in the header file simply declares a single array, named items, as an instance variable. We will hold the many items to be displayed in the user interface of our application in this array.

Open the MyDataSource.m file, and edit it to match the following code:

#import "MyDataSource.h"
#import "FoodItem.h"

@implementation MyDataSource
- (id)init
                        {
                            [super init];

                            // Some initial data for our interface
                            FoodItem * chimi = [[FoodItem alloc] init];                   // a
                            FoodItem * fajitas = [[FoodItem alloc] init];

                            [chimi setName:@"Chimichanga"];
                            [chimi setPrice:[NSNumber numberWithFloat:8.95]];
                            [fajitas setName:@"Steak Fajitas"];
                            [fajitas setPrice:[NSNumber numberWithFloat:10.95]];
                            items = [[NSMutableArray alloc] init];
                            [items addObject:chimi];
                            [items addObject:fajitas];
                            [chimi release];
                            [fajitas release];                                            // b
                            return self;
                        }

                        - (int)numberOfRowsInTableView:(NSTableView *)tableView         
                        {
                            return [items count];                                         // c
                        }

                        - (id)tableView:(NSTableView *)tableView               
                        objectValueForTableColumn:(NSTableColumn *)tableColumn
                                    row:(int)row
                        {
                            NSString * identifier = [tableColumn identifier];             // d
                            FoodItem * item = [items objectAtIndex:row];                  // e
                            return [item valueForKey:identifier];                         // f
                        }

@end

The code that we added performs the following tasks:

Save the project (File → Save, or

-S), and then build and run the application (Build → Build and Run, or

-R). You should see something like Figure 9-9.

Gets the identifier of the column for which the table view wants to set data.

Obtains the food item that is at the specified index in the array.

Sets the property of the food item that matches the identifier that we obtained in step 1.

We’re going to add a button to the interface. To enable a new row to be added when this button is pushed, we’ll need to add an action newButtonPressed: and an outlet table to MyDataSource. An easy way to do this is to add the declarations yourself in the code. In Project Builder, edit the MyDataSource.h file to match the following code. The code you need to add is shown in boldface.

#import <Cocoa/Cocoa.h>

@interface MyDataSource : NSObject
{
    NSMutableArray * items;
    IBOutlet NSTableView * table;
}
- (IBAction)newButtonPressed:(id)sender;

@end

Save the header file (File → Save, or

-S).

In Interface Builder’s Classes pane, select MyDataSource, and reload the source file (Classes → Read MyDataSource.h). This causes Interface Builder to reparse the header file and pick up the new outlet and action.

Resize the table view to make room for a button.

Drag a button from the Cocoa-Views panel onto the interface, and change its name to New Item.

Select the table view, and reset its Autosizing attributes as shown in Figure 9-10.

Figure 9-10. Adding a button to Menu

Control-drag a connection between the MyDataSource object in the Instances tab of the MainMenu.nib window and the table view. Connect it to the table outlet, as shown in Figure 9-11.

Figure 9-11. Connecting the table view to the table outlet

Control-drag a connection between the New Item button and the MyDataSource object in the Instances tab. Connect it to the newActionPressed: button, as shown in Figure 9-12.

Figure 9-12. Connecting the button to the data source

Save the nib file (File → Save, or

-S), and return to Project Builder.

Edit the MyDataSource.m file, adding the newButtonPressed: method shown in the following code:

                        - (IBAction)newButtonPressed:(NSEvent *)event {
                            FoodItem * item = [[FoodItem alloc] init];                     // a

                            [items insertObject:item atIndex:0];                           // b
                            [item release];
                            [table reloadData];                                            // c
                            [table selectRow:0 byExtendingSelection:NO];                   // d
                        }

The code we added performs the following tasks:

Save the project files (File → Save, or

-S), and then build and run the application (Build → Build and Run, or

-R). When you press the New Item button, a new row should be created, as shown in Figure 9-13.

In Project Builder, open FoodItem.h and modify the @interface declaration as follows. Adding <NSCoding> declares that the Song class conforms to the coding protocol.

#import <Foundation/Foundation.h>

@interface FoodItem : NSObject <NSCoding> {
    NSString * name;
    NSNumber * price;
}

.
.
.

NSCoding appears in brackets to signify that the FoodItem interface implements the coding protocol. If you were to read this declaration aloud, it would sound like: "FoodItem extends from the NSObject class and implements the NSCoding protocol.”

Open the FoodItem.m file, and add the NSCoding methods after the init method as follows:

                        - (id)initWithCoder:(NSCoder *)coder
                        {
                            [super init];
                            [self setName:[coder decodeObject]];                             // a
                            [self setPrice:[coder decodeObject]];                            // b
                            return self;
                        }

                        - (void)encodeWithCoder:(NSCoder *)coder
                        {
                            [coder encodeObject:[self name]];                                // c
                            [coder encodeObject:[self price]];                               // d
                        }

The code we added performs the following tasks:

Open MyDataSource.h, and add the following two action methods:

#import <Cocoa/Cocoa.h>

@interface MyDataSource : NSObject
{
    NSMutableArray * items;
    IBOutlet NSTableView * table;
}

- (IBAction)newButtonPressed:(id)sender;
- (IBAction)save:(id)sender;
                        - (IBAction)open:(id)sender;

@end

Save the source files, and then open the MainMenu.nib file in Interface Builder.

Reparse the MyDataSource.h file in Interface Builder. To do this, click on the MyDataSource object in the Classes tab, and then select the Classes → Read File MyDataSource.h menu option.

Click on the File menu of the MainMenu.nib - MainMenu window to reveal the menu options.

Control-drag a connection from the File → Open... menu item to the MyDataSource instance in the Instances tab, as shown in Figure 9-14. Connect it to the open: target.

Figure 9-14. Connecting the Open... menu item to MyDataSource

Control-drag a connection from the File → Save menu item to the MyDataSource instance. Connect it to the save: target.

Save the nib file (File → Save, or

-S), and return to Project Builder.

Add the save: and open: methods to MyDataSource.m, as well as two helper methods, as shown here:

#import "MyDataSource.h"
#import "FoodItem.h"

@implementation MyDataSource


.
.
.
- (IBAction)save:(id)sender
                        {
                            NSSavePanel * savePanel = [NSSavePanel savePanel];                  // a
                            SEL sel = @selector(savePanelDidEnd:returnCode:contextInfo:);       // b
                            [savePanel beginSheetForDirectory:@"~/Documents"                    // c
                                                         file:@"menu.items"
                                               modalForWindow:[table window]
                                                modalDelegate:self
                                               didEndSelector:sel
                                                  contextInfo:nil];
                        }

                        - (void)savePanelDidEnd:(NSSavePanel *)sheet
                                     returnCode:(int)returnCode
                                    contextInfo:(void *)context
                        {
                            if (returnCode == NSOKButton) {                                     // d
                                [NSArchiver archiveRootObject:items toFile:[sheet filename]];
                            }
                        }

                        - (IBAction)open:(id)sender
                        {
                            NSOpenPanel * openPanel = [NSOpenPanel openPanel];                  // e
                            SEL sel = @selector(openPanelDidEnd:returnCode:contextInfo:);
                            [openPanel beginSheetForDirectory:@"~/Documents"
                                                         file:nil
                                                        types:nil
                                               modalForWindow:[table window]
                                                modalDelegate:self
                                               didEndSelector:sel
                                                  contextInfo:nil];
                        }

                        - (void)openPanelDidEnd:(NSOpenPanel *)sheet
                                     returnCode:(int)returnCode
                                    contextInfo:(void *)contextInfo
                        {
                            if (returnCode == NSOKButton) {
                                NSMutableArray * array;                                         // f
                                array = [NSUnarchiver unarchiveObjectWithFile:[sheet filename]]; 
                                [array retain];
                                [items release];
                                items = array;
                                [table reloadData];
                            }
                        }

@end

The code that we added does the following things:

Now save the project (File → Save, or

-S), and then build and run the application (Build → Build and Run, or

-R).