Objective-C iOS Development for Legacy & Enterprise Apps · レッスン

API呼び出しのためのNSURLSession

NSURLSessionを使ってネットワークリクエストを実行し、レスポンスを処理し、RESTful APIとのデータ転送を管理します。

「API呼び出しのためのNSURLSession」はCoddyKit上の無料Objective-C iOS Development for Legacy & Enterprise Appsレッスンです。これはレッスン1/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはObjective-C iOS Development for Legacy & Enterprise Apps学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Objective-C iOS Development for Legacy & Enterprise Appsコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Connecting Your App to the World

Mobile apps often need to talk to the internet to fetch or send data. This is called networking.

Think of checking the weather, loading your social media feed, or sending a message. All these involve your app making requests to a server.

Servers expose APIs (Application Programming Interfaces), which are sets of rules for how your app can interact with them. Many modern APIs follow the REST architectural style.

Meet NSURLSession

In Objective-C, the primary way to perform network requests is using NSURLSession. It's a powerful and flexible API for downloading content over HTTP/HTTPS.

It replaced older methods like NSURLConnection.
It handles data tasks, download tasks, and upload tasks.
It supports background transfers and authentication.

NSURLSession makes network communication more efficient and easier to manage.

NSURLSession's Building Blocks

NSURLSession works with a few key components:

NSURLSession: The main object that coordinates network tasks.
NSURLSessionConfiguration: Defines the behavior of a session (e.g., caching, timeouts, cellular access).
NSURLSessionTask: An abstract class for tasks. Concrete subclasses include NSURLSessionDataTask (for data), NSURLSessionDownloadTask (for files), and NSURLSessionUploadTask (for uploading files).

Making a Simple GET Request

Let's make a basic GET request to fetch data from a server. A GET request is used to retrieve information.

We'll use NSURLSessionDataTask. This task takes a URL and a completion handler (a block of code) that runs when the request finishes.

Remember to call [task resume]; to start the task!

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // 1. Create a URL
        NSURL *url = [NSURL URLWithString:@"https://jsonplaceholder.typicode.com/todos/1"];

        // 2. Create a session (using the default shared session)
        NSURLSession *session = [NSURLSession sharedSession];

        // 3. Create a data task
        NSURLSessionDataTask *dataTask = [session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
            if (error) {
                NSLog(@"Error: %@", error.localizedDescription);
            } else {
                // Check for HTTP status code (e.g., 200 OK)
                NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
                if (httpResponse.statusCode == 200) {
                    NSString *responseString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
                    NSLog(@"Response Data: %@", responseString);
                } else {
                    NSLog(@"Server returned status code: %ld", (long)httpResponse.statusCode);
                }
            }
            CFRunLoopStop(CFRunLoopGetCurrent()); // Stop the run loop once task finishes
        }];

        // 4. Start the task
        [dataTask resume];

        // Keep the main thread alive until the async task completes
        CFRunLoopRun();
    }
    return 0;
}

Understanding the Response

The completion handler block for a data task provides three parameters:

data: The raw data received from the server (e.g., JSON, image bytes).
response: An NSURLResponse object, which can be cast to NSHTTPURLResponse for HTTP-specific details like status codes (200 OK, 404 Not Found, etc.) and headers.
error: An NSError object if something went wrong during the request (e.g., no internet connection, server unreachable).

Always check for error first, then the HTTP status code.

Decoding JSON Responses

Most REST APIs return data in JSON (JavaScript Object Notation) format. This is a lightweight, human-readable data interchange format.

Objective-C provides NSJSONSerialization to convert raw NSData into Objective-C objects (NSDictionary or NSArray) and vice-versa.

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSURL *url = [NSURL URLWithString:@"https://jsonplaceholder.typicode.com/todos/1"];
        NSURLSession *session = [NSURLSession sharedSession];
        NSURLSessionDataTask *dataTask = [session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
            if (error) {
                NSLog(@"Error: %@", error.localizedDescription);
            } else {
                NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
                if (httpResponse.statusCode == 200) {
                    NSError *jsonError = nil;
                    // Attempt to parse JSON data
                    id jsonObject = [NSJSONSerialization JSONObjectWithData:data
                                                                    options:0 // No special options
                                                                      error:&jsonError];
                    if (jsonError) {
                        NSLog(@"JSON Parsing Error: %@", jsonError.localizedDescription);
                    } else if ([jsonObject isKindOfClass:[NSDictionary class]]) {
                        NSDictionary *todoItem = (NSDictionary *)jsonObject;
                        NSLog(@"Todo Title: %@", todoItem[@"title"]);
                        NSLog(@"Completed: %@", todoItem[@"completed"] ? @"YES" : @"NO");
                    } else {
                        NSLog(@"Received unexpected JSON format.");
                    }
                } else {
                    NSLog(@"Server returned status code: %ld", (long)httpResponse.statusCode);
                }
            }
            CFRunLoopStop(CFRunLoopGetCurrent());
        }];
        [dataTask resume];
        CFRunLoopRun();
    }
    return 0;
}

Tailoring NSURLSession with Configuration

For more control, you can create a custom NSURLSession using an NSURLSessionConfiguration object.

Common configurations include:

defaultSessionConfiguration: Uses a global shared cookie storage, credential storage, and disk-based cache.
ephemeralSessionConfiguration: Similar to default, but stores no data to disk (e.g., no caches, cookies). Ideal for private browsing.
backgroundSessionConfigurationWithIdentifier:: Allows transfers to continue when your app is suspended or terminated.

You can set properties like timeoutIntervalForRequest, HTTPAdditionalHeaders, and more.

Sending Data with POST

While GET retrieves data, POST requests are used to send new data to the server (e.g., submitting a form, creating a new resource).

For POST, you typically create an NSURLRequest object, set its HTTP method to "POST", and attach the data you want to send as HTTPBody.

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSURL *url = [NSURL URLWithString:@"https://jsonplaceholder.typicode.com/posts"];
        NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
        request.HTTPMethod = @"POST"; // Set HTTP method to POST

        // Prepare data to send (e.g., a new post title and body)
        NSDictionary *postData = @{
            @"title": @"foo",
            @"body": @"bar",
            @"userId": @1
        };
        NSError *jsonError = nil;
        NSData *jsonData = [NSJSONSerialization dataWithJSONObject:postData options:0 error:&jsonError];

        if (jsonError) {
            NSLog(@"JSON serialization error: %@", jsonError.localizedDescription);
            CFRunLoopStop(CFRunLoopGetCurrent());
            return 1;
        }

        request.HTTPBody = jsonData;
        [request setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
        [request setValue:@"application/json" forHTTPHeaderField:@"Accept"];

        NSURLSession *session = [NSURLSession sharedSession];
        NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
            if (error) {
                NSLog(@"Error: %@", error.localizedDescription);
            } else {
                NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
                if (httpResponse.statusCode >= 200 && httpResponse.statusCode < 300) {
                    NSString *responseString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
                    NSLog(@"POST Success! Response: %@", responseString);
                } else {
                    NSLog(@"Server returned status code: %ld", (long)httpResponse.statusCode);
                }
            }
            CFRunLoopStop(CFRunLoopGetCurrent());
        }];
        [dataTask resume];
        CFRunLoopRun();
    }
    return 0;
}

Handling Network Errors Gracefully

Network requests can fail for many reasons. Robust error handling is crucial for a good user experience.

Check the error object first: This indicates fundamental issues like no internet, DNS lookup failure, or server connection problems.
Check NSHTTPURLResponse status code: After confirming no error, check the HTTP status code (e.g., 400 Bad Request, 401 Unauthorized, 500 Internal Server Error).
Provide user feedback: Inform the user about the issue, e.g., "No internet connection" or "Could not load data."

Always assume network requests can fail and plan for it!

Quick Check: NSURLSession

Consider the following Objective-C code snippet for a network request:

NSURL *url = [NSURL URLWithString:@"https://example.com/data"];
NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *task = [session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
    if (error) {
        NSLog(@"Failed with error: %@", error.localizedDescription);
    } else {
        NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
        if (httpResponse.statusCode == 200) {
            NSLog(@"Data received!");
        } else {
            NSLog(@"HTTP Status: %ld", (long)httpResponse.statusCode);
        }
    }
}];
// Missing line here

Recap: Mastering NSURLSession

In this lesson, we explored how to perform network requests using NSURLSession in Objective-C.

We learned about NSURLSession, NSURLSessionConfiguration, and NSURLSessionTask.
You can make GET requests to fetch data and POST requests to send data.
We covered how to handle the response, including checking for errors and parsing JSON data using NSJSONSerialization.
Always remember to call [task resume]; to start a task and implement robust error handling.

Next, you'll dive into concurrency with Grand Central Dispatch to keep your UI responsive during network operations!

よくある質問

「API呼び出しのためのNSURLSession」レッスンは無料ですか？

はい。「API呼び出しのためのNSURLSession」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Objective-C iOS Development for Legacy & Enterprise Appsコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Objective-C iOS Development for Legacy & Enterprise Appsコースには全4レッスンが含まれています。

「API呼び出しのためのNSURLSession」で何を学びますか？

NSURLSessionを使ってネットワークリクエストを実行し、レスポンスを処理し、RESTful APIとのデータ転送を管理します。ブラウザで直接実行するハンズオンコードでObjective-C iOS Development for Legacy & Enterprise Appsを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Objective-C iOS Development for Legacy & Enterprise Appsを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのObjective-C iOS Development for Legacy & Enterprise Appsは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン1/4です。

「API呼び出しのためのNSURLSession」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このObjective-C iOS Development for Legacy & Enterprise Appsレッスンでコードを書いて実行できますか？

はい。すべてのObjective-C iOS Development for Legacy & Enterprise Appsレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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