iOS NSURL 帶參數 POST 請求正確寫法

問題現象

使用 NSURL URLWithString: 構建帶查詢參數的 URL 時，編譯錯誤 Too many arguments expects 1 have 2。

錯誤代碼

NSString *myString = @"1994";
NSURL *url = [NSURL URLWithString:@"https://example.com/api.php/?data=%@", myString];
// 錯誤：URLWithString: 只接受 1 個參數，無法直接格式化

正確構建 URL

NSString *myString = @"1994";
// 先用 stringWithFormat 組合完整字串，再建立 NSURL
NSString *urlString = [NSString stringWithFormat:@"https://example.com/api.php/?data=%@", myString];
NSURL *url = [NSURL URLWithString:urlString];
// 或使用 NSURLComponents (iOS 7+ 推薦)
NSURLComponents *components = [NSURLComponents componentsWithString:@"https://example.com/api.php/"];
components.queryItems = @[[NSURLQueryItem queryItemWithName:@"data" value:myString]];
NSURL *url = components.URL; // 自動處理編碼

完整 POST 請求範例 (同步)

NSString *myString = @"1994";
NSString *postBody = [NSString stringWithFormat:@"data=%@", myString];
NSURL *url = [NSURL URLWithString:@"https://example.com/api.php/"]; // 基礎 URL

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:@"POST"];
[request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];

NSData *postData = [postBody dataUsingEncoding:NSUTF8StringEncoding];
[request setHTTPBody:postData];
[request setValue:[NSString stringWithFormat:@"%lu", (unsigned long)postData.length] 
      forHTTPHeaderField:@"Content-Length"];

NSError *error = nil;
NSHTTPURLResponse *response = nil;
NSData *responseData = [NSURLConnection sendSynchronousRequest:request 
                                            returningResponse:&response 
                                                        error:&error];

if (!error && response.statusCode >= 200 && response.statusCode < 300) {
    NSString *result = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
    NSLog(@"回應: %@", result);
} else {
    NSLog(@"錯誤: %@, 狀態碼: %ld", error, (long)response.statusCode);
}

現代非同步寫法 (NSURLSession)

NSURLSession *session = [NSURLSession sharedSession];
NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
    if (!error) {
        NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
        if (httpResponse.statusCode == 200) {
            NSString *result = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
            dispatch_async(dispatch_get_main_queue(), ^{
                // 更新 UI
                NSLog(@"非同步回應: %@", result);
            });
        }
    } else {
        NSLog(@"網路錯誤: %@", error);
    }
}];
[task resume];

關鍵點總結

1. URL 構建：先格式化字串，再建立 NSURL；推薦 NSURLComponents 自動處理編碼
2. POST 資料：setHTTPBody: 需 NSData，編碼用 NSUTF8StringEncoding
3. Header：設定 Content-Type 為 application/x-www-form-urlencoded
4. 同步/非同步：主執行緒禁用同步請求，生產環境必須用 NSURLSession 非同步