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RanchForecast Project

It just so happens that the Big Nerd Ranch Web site has an XML feed of upcoming classes. In this exercise, you are going to write an application that uses this Web service to show the upcoming classes at Big Nerd Ranch in a table view. The app will look like Figure 28.4.

Figure 28.4. Completed Application

Create a new project of type Cocoa Application. Disable Create Document-Based Application, Uses Core Data, and Create Unit Tests. Name the project RanchForecast. Set the Class Prefix to RanchForecast also.

We’ll build this application from the model upward. Create a new Objective-C class called ScheduledClass that subclasses NSObject. Add four properties: name, location, href, and begin in ScheduledClass.h:

#import

@interface ScheduledClass : NSObject {

NSString *name;

NSString *location;

NSString *href;

NSDate *begin;

}

@property (nonatomic, copy) NSString *name;

@property (nonatomic, copy) NSString *location;

@property (nonatomic, copy) NSString *href;

@property (nonatomic, strong) NSDate *begin;

@end

Then synthesize the properties in ScheduledClass.m:

#import "ScheduledClass.h"

@implementation ScheduledClass

@synthesize name, location, href, begin;

@end

With a simple model, it can often be tempting to use an NSDictionary. Frequently, however, taking the time to create a class will make life easier in the long run, especially when a project grows beyond its initial scope.

NSURLConnection

Now that we have the model defined, we will turn our attention to fetching the data from the Web service. In Cocoa, this is typically done using the NSURLConnection class. In order to create a connection, we must first create an NSURLRequest, which describes the request to the connection object. NSURLRequest is sufficient for simple requests. Requests requiring more conrol, such as specific request headers, should use NSMutableURLRequest.

NSURLConnection can be used synchronously and asynchronously. In a synchronous connection, the current thread blocks while the request is completed, making it unsuitable for use in the main thread, as this will make the user interface unresponsive while the request is completed.

Asynchronous connections are scheduled in the run loop, and a delegate is specified to respond to various events in the connection’s lifetime. In this chapter, we will use an synchronous connection for simplicity.

Create a new subclass of NSObject called ScheduleFetcher. This class will encapsulate the hard work of communicating with the Web service and parsing the result into the model object. By abstracting away this functionality, we keep our user interface controller classes simple and uncluttered, and we can easily use this class in other projects. Define the interface in ScheduleFetcher.h:

#import

@interface ScheduleFetcher : NSObject {

NSMutableArray *classes;

NSMutableString *currentString;

NSMutableDictionary *currentFields;

NSDateFormatter *dateFormatter;

}

// Returns an NSArray of ScheduledClass objects if successful.

// Returns nil on failure.

- (NSArray *)fetchClassesWithError:(NSError **)outError;

@end

Define init and fetchClassesWithError: in ScheduleFetcher.m:

#import "ScheduleFetcher.h"

#import "ScheduledClass.h"

@implementation ScheduleFetcher

- (id)init

{

self = [super init];

if (self) {

classes = [[NSMutableArray alloc] init];

dateFormatter = [[NSDateFormatter alloc] init];

[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss zzzz"];

}

return self;

}

- (NSArray *)fetchClassesWithError:(NSError **)outError

{

NSURL *xmlURL = [NSURL URLWithString:

@"http://bignerdranch.com/xml/schedule"];

NSURLRequest *req = [NSURLRequest requestWithURL:xmlURL

cachePolicy:NSURLRequestReturnCacheDataElseLoad

timeoutInterval:30];

NSURLResponse *resp = nil;

NSData *data = [NSURLConnection sendSynchronousRequest:req

returningResponse:&resp

error:outError];

if