FetchOperation.h

#import <Foundation/Foundation.h>


@interface FetchOperation : NSOperation {
	NSURLRequest *request;
	NSURLConnection *connection;
	NSHTTPURLResponse *response;
	NSMutableData *responseBody;
	
	NSOperation *parseOperation;
	
	BOOL ready;
	BOOL executing;
	BOOL finished;
	BOOL cancelled;
}

@property (nonatomic, copy) NSURLRequest *request;

- (void)parseResponseBody:(NSData *)bodyData;

@end

FetchOperation.m

#import "FetchOperation.h"

#import "AppDelegate.h"


@implementation FetchOperation


#pragma mark Properties


@synthesize request;


- (void)setReady:(BOOL)b {
	if (ready != b) {
		[self willChangeValueForKey:@"isReady"];
		ready = b;
		[self didChangeValueForKey:@"isReady"];
	}
}
- (void)setExecuting:(BOOL)b {
	if (executing != b) {
		[self willChangeValueForKey:@"isExecuting"];
		executing = b;
		[self didChangeValueForKey:@"isExecuting"];
	}
}
- (void)setFinished:(BOOL)b {
	if (finished != b) {
		[self willChangeValueForKey:@"isFinished"];
		finished = b;
		[self didChangeValueForKey:@"isFinished"];
	}
}
- (void)setCancelled:(BOOL)b {
	if (cancelled != b) {
		[self willChangeValueForKey:@"isCancelled"];
		cancelled = b;
		[self didChangeValueForKey:@"isCancelled"];
	}
}


#pragma mark Init/dealloc


- (id) init {
	if (self = [super init]) {
		parseOperation = nil;
		ready = YES;
		executing = NO;
		finished = NO;
		cancelled = NO;
	}
	return self;
}

- (void) dealloc {
	[request release];
	[connection release];
	[response release];
	[responseBody release];
	
	if (parseOperation) {
		[parseOperation removeObserver:self forKeyPath:@"isFinished"];
		[parseOperation removeObserver:self forKeyPath:@"isCancelled"];
		[parseOperation release];
		parseOperation = nil;
	}
	
 	[super dealloc];
}


#pragma mark NSOperation


- (BOOL)isConcurrent {
	// FetchOperation runs in concurrent mode, managed manually.
	return YES;
}

- (void)start {
	// Follows the behavior of NSOperation in Mac OS 10.6 (and iPhone OS 3.0)
	// また、start前にrequestがセットされていない場合にも例外を発生させる
	if (finished || cancelled) {
		[self cancel];
		return;
	}
	if (!ready || executing || !request) {
		@throw NSInvalidArgumentException;
	}
	
	// サーバーと通信可能かどうかを確認する
	// 通信出来ない場合には何もしないで終了する
	AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
	if (!appDelegate.internetConnectionAvailable) {
		NSLog(@"Device is not reachable to the API server. Aborting.");
		[self cancel];
		return;
	}
	
	// connectionの準備を行う。準備だけ。実行はmainで非同期的に。
	connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
	if (!connection) {
		@throw NSInvalidArgumentException;
	}
	
	// main実行直前に状態を変更する、その後実行。
	[self setReady:NO];
	[self setExecuting:YES];
	[self setFinished:NO];
	[self setCancelled:NO];
	// mainのためにスレッドを作る必要がない、main自体が非同期関数だけで出来ているので
	[self main];
}

- (void)cancel {
	// 通信をキャンセルして、状態をキャンセル状態にする。
	[connection cancel];
	[self setReady:NO];
	[self setExecuting:NO];
	[self setFinished:YES];
	[self setCancelled:YES];
}

- (BOOL)isReady {
	return ready;
}

- (BOOL)isExecuting {
	return executing;
}

- (BOOL)isFinished {
	return finished;
}

- (BOOL)isCancelled {
	return cancelled;
}

- (void)main {
	// DO NOT override this method in subclasses. Use parseResponseBody instead.
	// iOS4に対応するため、currentRunLoopではなくmainRunLoopを使う必要があります。
	// ※iOS4はMac OS 10.6と同じNSOperationの挙動になるため。詳細はブログに書きます
	NSLog(@" * Executing API %@", [self.request URL]);
	[connection scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
	[connection start];
}


#pragma mark NSURLConnection


- (void)connection:(NSURLConnection*)sender didReceiveResponse:(NSHTTPURLResponse*)res {
	NSLog(@" * Response received for API %@", [self.request URL]);
	
	// didReceiveResponseは極稀にひとつの接続で複数回呼ばれることがあるので、その点に注意して書く。
	// まずはレスポンスとボディを格納する準備をする。
	if (response) {
		[response release];
		response = nil;
	}
	if (responseBody) {
		[responseBody release];
		responseBody = nil;
	}
	responseBody = [[NSMutableData alloc] init];
	
	// レスポンスが飛んできたので確保する
	// レスポンスが200以外であれば即座にキャンセルして終了する
	response = [res retain];
	if ([response statusCode] != 200) {
		NSLog(@"Error while executing API: invalid HTTP status code %d has been returned", [response statusCode]);
		[self cancel];
		AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
		[appDelegate showConnectionAlertOnMainThreadWithMessage:@"エラーだよーん"];
		return;
	}
}

- (void)connection:(NSURLConnection*)sender didReceiveData:(NSData*)data {
	// データが送られてきたら都度キャッシュに突っ込む
	[responseBody appendData:data];
}

- (void)connection:(NSURLConnection*)sender didFailWithError:(NSError*)error {
	// 接続に失敗したらキャンセル状態にして、タイムアウトエラーメッセージを出す
	[self cancel];
	AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
	[appDelegate showConnectionAlertOnMainThreadWithMessage:@"接続失敗だよーん"];
}

- (void)connectionDidFinishLoading:(NSURLConnection*)sender {
	NSLog(@" * Data load completed for API %@", [self.request URL]);
	
	// parseMainを別スレッドで起動して続きを行う
	// スレッドの完了通知を受け取ってからこのオペレーションを終了させること
	parseOperation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(parseMain:) object:nil];
	[parseOperation addObserver:self
					 forKeyPath:@"isFinished"
						options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld)
						context:NULL];
	[parseOperation addObserver:self
					 forKeyPath:@"isCancelled"
						options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld)
						context:NULL];
	AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
	[appDelegate.parseOperationQueue addOperation:parseOperation];
}

- (NSURLRequest *)connection:(NSURLConnection *)sender willSendRequest:(NSURLRequest *)req redirectResponse:(NSURLResponse *)res {
	// リダイレクト要請は常に受け入れてリダイレクトする
	return req;
}


#pragma mark Method


- (void)parseResponseBody:(NSData *)bodyData {
	// Default implementation does nothing.
	// Override this method to parse the response data.
	return;
}


#pragma mark NSThread


- (void)parseMain:(id)sender {
	NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
	AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
	// すべての通信が完了したので、responseBodyのチェック。responseBodyがnullであれば何らかのエラーがあったと考えられるのでキャンセルして終了。
	if (!response || !responseBody) {
		NSLog(@"Error while executing API: Neither response nor body are returned from the server.");
		[self cancel];
		[appDelegate showConnectionAlertOnMainThreadWithMessage:@"レスポンスが帰ってこなかったよーん"];
		return;
	}
	
	// チェック完了。responseBodyを渡してparseする。
	// parseResponseBodyは同期的に、かつロックを掛けて実行されるので注意。ロックの解放はfinallyで行う。
	@try {
		[appDelegate.managedObjectContext lock];
		[self parseResponseBody:responseBody];
	}
	@catch (NSException *e) {
		// DO NOT throw exceptions out from NSOperation in order not to stop the entire application.
		NSLog(@"Error while parsing API response: %@", e);
	}
	@finally {
		[appDelegate.managedObjectContext unlock];
		// パースも完了、すべての処理が終了。pool releaseはfinallyに入れておかないとエラー時に実行されなくなりメモリが漏れる
		[pool release];
	}
}


#pragma mark -
#pragma mark NSKeyValueObserving


- (void)observeValueForKeyPath:(NSString *)keyPath
					  ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context {
	
	// ParseOperationの状況に応じて自身の状況を変化させる
    if ([keyPath isEqual:@"isFinished"]) {
		[self setReady:NO];
		[self setExecuting:NO];
		[self setFinished:YES];
		[self setCancelled:NO];
    } else if ([keyPath isEqual:@"isCancelled"]) {
		[self cancel];
	}
	
	// ParseOperationを開放する
	[parseOperation removeObserver:self forKeyPath:@"isFinished"];
	[parseOperation removeObserver:self forKeyPath:@"isCancelled"];
	[parseOperation release];
	parseOperation = nil;
}

@end