Question

我知道这是一个愚蠢的问题，但我无法找到解决方案。

这是我的代码：
ConnectionService.h。

#import "LaunchScreenViewController.h"
@interface ConnectionService : NSObject

-(void)getsFeaturedProducts;

@end

ConnectionService.m

-(void)getsFeaturedProducts {
NSString *urlString = [NSString stringWithFormat:@"my-url",[[AppDelegate instance] getUrl]];
    NSURL *url = [NSURL URLWithString:urlString];

    NSURLSessionDataTask *getData = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData* data, NSURLResponse *response, NSError* error){
        NSString* rawJson = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        NSDictionary *value = [rawJson JSONValue];
        _featuredProducts = [[NSDictionary alloc]initWithDictionary:value];
        NSLog(@"Featured products: %@", _featuredProducts);//not empty

        LaunchScreenViewController *lsvc = [[LaunchScreenViewController alloc]init];
        lsvc.featuredProducts = self.featuredProducts;
NSLog(@"Featured products: %@", lsvc.featuredProducts);//not empty
    }];
    [getData resume];
}

LaunchScreenViewController.h

#import "ConnectionService.h"

@interface LaunchScreenViewController : UIViewController
@property(nonatomic,strong) NSDictionary *featuredProducts;
@end

LaunchScreenViewController.m

- (void)viewDidAppear:(BOOL)animated{
    [super viewDidAppear:YES];

    ConnectionService *connectionService = [[ConnectionService alloc]init];
    [connectionService refreshProducts];

    self.featuredProducts = [[NSDictionary alloc]init];
    NSLog(@"featuredProducts: %@", self.featuredProducts);//empty
    NSArray *keys = [[NSArray alloc]initWithArray:[self.featuredProducts allKeys]];
    NSLog(@"All featured product keys: %@", keys);
}

我做错了什么？

P.S。编程目标-c少于一个月，所以是的...谢谢-rep。

Answer 1

你认为这个异步问题是错误的 - 但你并不遥远。以下是您的代码现在正在做的事情：

创建了一个LaunchScreenViewController实例。
LaunchScreenViewController的实例创建了ConnectionService的实例
ConnectionService查询异步数据
返回数据后，它会创建LaunchScreenViewController的 BRAND NEW 实例并将其传递给数据。
您检查原始的LaunchScreenViewController是否有数据，但没有 - 它转而使用新实例。

您希望将数据传回原始的LaunchScreenViewController。有几种方法可以做到这一点。我会告诉你一个并链接到第二个。

让我们举例说明如何通过NSNotificationCenter将数据传回原始控制器：

LaunchScreenViewController.m

- (void)viewDidLoad:(BOOL)animated{
    //Your current code....

    [[NSNotificationCenter defaultCenter] addObserver:self
    selector:@selector(receiveConnectionData:) 
    name:@"ConnectionDataReceived"
    object:nil];

}

- (void) receiveTestNotification:(NSNotification *) notification
{
    // [notification name] should always be @"ConnectionDataReceived"
    // unless you use this method for observation of other notifications
    // as well.

    if ([[notification name] isEqualToString:@"ConnectionDataReceived"]){

        self.featuredProducts = [[NSDictionary alloc]init];
        NSLog(@"featuredProducts: %@", self.featuredProducts);//empty
        NSArray *
        NSArray *keys = [[NSArray alloc]initWithArray:[notification.object allKeys]];
        NSLog(@"All featured product keys: %@", keys);
        NSLog (@"Successfully received the test notification!");
    }
}

在您的ConnectionService.h

-(void)getsFeaturedProducts {
    NSString *urlString = [NSString stringWithFormat:@"my-url",[[AppDelegate instance] getUrl]];
    NSURL *url = [NSURL URLWithString:urlString];

    NSURLSessionDataTask *getData = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData* data, NSURLResponse *response, NSError* error){
        NSString* rawJson = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        NSDictionary *value = [rawJson JSONValue];
        _featuredProducts = [[NSDictionary alloc]initWithDictionary:value];
        NSLog(@"Featured products: %@", _featuredProducts);//not empty

        //Pass the NSDictionary back to the ORIGINAL LaunchViewController
        [[NSNotificationCenter defaultCenter]  postNotificationName:@"ConnectionDataReceived"  _featuredProducts];
}];
[getData resume];

}

注意：您也可以使用Delegate来完成此操作，这更复杂但更强大。你可以在这里找到Chris Mills的一个很好的教程：https://coderchrismills.wordpress.com/2011/05/05/basic-delegate-example/

Answer 2

您需要将结果返回给控制器。

您需要做的是在您的 - （void）getsFeaturedProducts函数中添加一个完成块，然后在返回结果后立即调用它传回结果。

在同一个功能中，您可以使用正确的数据重新加载视图。

<强>服务：

PYSPARK_PYTHON

<强>控制器：

-(void)getsFeaturedProducts:(void (^)(NSDictionary *featuredProducts))completionHandler {
      NSString *urlString = [NSString stringWithFormat:@"my-url",[[AppDelegate instance] getUrl]];
NSURL *url = [NSURL URLWithString:urlString];

      NSURLSessionDataTask *getData = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData* data, NSURLResponse *response, NSError* error){
          NSString* rawJson = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
          NSDictionary *featuredProducts = [rawJson JSONValue];
          completionHandler(featuredProducts);
      }];
     [getData resume];
}

}

Answer 3

您的代码无效，因为使用LaunchScreenViewController创建的alloc init实例不是在Storyboard / XIB文件中创建的实例。

从另一个类异步检索数据的推荐方法是完成处理程序。

在 ConnectionService.m 中使用完成处理程序实现该方法，并在.h文件中相应地声明它。

- (void)getsFeaturedProductsWithCompletion:(void (^)(NSDictionary *products))completion
{
  NSString *urlString = [NSString stringWithFormat:@"my-url",[[AppDelegate instance] getUrl]];
  NSURL *url = [NSURL URLWithString:urlString];

  NSURLSessionDataTask *getData = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData* data, NSURLResponse *response, NSError* error){
    NSString* rawJson = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSDictionary *value = [rawJson JSONValue];
    completion(value);
  }];
  [getData resume];
}

附注：强烈建议在数据任务中添加错误处理!!

在 LaunchScreenViewController.h 中声明ConnectionService实例的属性

#import "ConnectionService.h"

@interface LaunchScreenViewController : UIViewController
@property(nonatomic,strong) NSDictionary *featuredProducts;
@property(nonatomic,strong) ConnectionService *connectionService;
@end

在 LaunchScreenViewController.m 中调用方法

- (void)viewDidAppear:(BOOL)animated{
  [super viewDidAppear:YES];

  connectionService = [[ConnectionService alloc]init];
  [connectionService getsFeaturedProductsWithCompletion:^(NSDictionary *products) {
    self.featuredProducts = products;
    NSLog(@"featuredProducts: %@", self.featuredProducts);//empty
    NSArray *keys = [[NSArray alloc]initWithArray:[self.featuredProducts allKeys]];
    NSLog(@"All featured product keys: %@", keys);
    connectionService = nil; // release the connectionService instance if needed
  }];
}

Answer 4

-(void)getsFeaturedProducts {
NSString *urlString = [NSString stringWithFormat:@"my-url",[[AppDelegate instance] getUrl]];
NSURL *url = [NSURL URLWithString:urlString];
NSURLSessionDataTask *getData = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData* data, NSURLResponse *response, NSError* error){
    dispatch_async(dispatch_get_main_queue(), ^{
        NSString* rawJson = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        NSDictionary *value = [rawJson JSONValue];
        _featuredProducts = [[NSDictionary alloc]initWithDictionary:value];
        NSLog(@"Featured products: %@", _featuredProducts);//not empty

        LaunchScreenViewController *lsvc = [[LaunchScreenViewController alloc]init];
        lsvc.featuredProducts = self.featuredProducts;
        [[[UIApplication sharedApplication] keyWindow] setRootViewController:lsvc];
    })

}];
[getData resume];
}

尝试将数据从异步调用传输到另一个类

4 个答案: