如何从使用NSURLConnection的类及其委托类返回一个对象？

Question

我正在尝试将代码从UITableViewController类移动到"helper"类.

该代码利用NSURLConnection来获取和解析JSON,然后填充NSMutableArray.

我想要做的是在我的助手类中调用一个返回NSMutableArray的方法.我不明白的是如何从NSURLConnection的connectionDidFinishLoading委托类(实际构建数组)返回数组,就像它来自最初调用的启动连接的方法一样.换句话说,调用NSURLConnection的方法如何获得控制权,以便它可以从整个操作中返回一个值？

以下是帮助程序类的相关方法.如何让getMovies方法返回在connectionDidFinishLoading委托类中构建的listOfMovies？

-(NSMutableArray)getMovies:(NSURL*)url {

responseData = [[NSMutableData data] retain];       

NSURLRequest *request = [NSURLRequest requestWithURL:url];
//NSURLRequest* request = [NSURLRequest requestWithURL: url cachePolicy: NSURLRequestUseProtocolCachePolicy timeoutInterval: 30.0];

connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];

}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {

[responseData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
[responseData appendData:data];
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
//TODO error handling for connection
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {      

//---initialize the array--- 

listOfMovies = [[NSMutableArray alloc] init];

tmdbMovies = [[NSArray alloc] init];
posters = [[NSArray alloc] init];
thumbs = [[NSDictionary alloc] init];

NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];

SBJsonParser *json = [[SBJsonParser new] autorelease];

tmdbMovies = [json objectWithString:responseString];

// loop through all the top level elements in JSON
for (id movie in tmdbMovies) {

    // 0 - Name
    // 1 - Meta
    // 2 - Url


    if ((NSNull *)[movie objectForKey:@"name"] != [NSNull null]) {

        if (![[movie objectForKey:@"name"] isEqualToString:@""]) {
            name = [movie objectForKey:@"name"];
        }

    } 

    if ((NSNull *)[movie objectForKey:@"info"] != [NSNull null]) {

        if (![[movie objectForKey:@"info"] isEqualToString:@""]) {
            meta = [movie objectForKey:@"info"];
        }

    } 

    if ((NSNull *)[movie objectForKey:@"thumb"] != [NSNull null]) {

        if (![[movie objectForKey:@"thumb"] isEqualToString:@""]) {
            thumbUrl = [movie objectForKey:@"thumb"];
        }

    } 

    NSLog(@"Name: %@", name);
    NSLog(@"Info: %@", meta);
    NSLog(@"Thumb: %@", thumbUrl);

    NSMutableArray *movieData = [[NSMutableArray alloc] initWithObjects:name,meta,thumbUrl,nil];

    // add movieData array to listOfJMovies array
    [listOfMovies addObject:movieData];


    [movieData release];
}


//FIXME: Connection warning
if (connection!=nil) { 
    [connection release]; 
}

[responseData release]; 
[responseString release];



}

Answer 1

你真正需要做的是创建一个@protocol为你的助手类创建一个委托.然后-(NSMutableArray)getMovies:(NSURL*)url改为-(void)getMovies:(NSURL*)url

调用helper方法的类需要实现helper方法的委托.

然后- (void)connectionDidFinishLoading:(NSURLConnection *)connection调用委托方法.最好有一个成功,一个成功.

=更新Begin =

您还需要id delegate在helper文件中定义一个调用类在init之后但在调用之前设置为self的文件-(void)getMovies:(NSURL*)url.这样,帮助文件知道回调的位置.

getMovies *movieListCall = [[getMovies alloc] init];
movieListCall.delegate = self;
[movieListCall getMovies:<your NSURL goes here>];

您将delegate在getMovies.h和getMovies.m文件中看到一些其他行以包含a .

=更新结束=

在你的getMovies.h文件中添加:

@protocol getMoviesDelegate

@required
- (void)getMoviesSucceeded:(NSMutableArray *)movieArray;
- (void)getMoviesFailed:(NSString *)failedMessage;

@end

@interface getMovies : NSOBject {
id delegate;
}

@property (nonatomic, assign) id delegate;

在你的getMovies.m文件中添加:

@synthesize delegate;

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    //TODO error handling for connection
    if ([delegate respondsToSelector:@selector(getMoviesFailed:)]) {
        [delegate getMoviesFailed:[error localizedDescription]];
    }
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {      

//finishes with
    if ([delegate respondsToSelector:@selector(getMoviesSucceeded:)]) {
        [delegate getMoviesSucceeded:listOfMovies];
    }
}

更新你的调用类.h文件使用getMoviesDelegate:

@interface MoviesView : UIViewController <getMoviesDelegate>{
.
.
.
}

将getMoviesDelegate方法添加到您的调用类.m文件中

- (void)getMoviesSucceeded:(NSMutableArray *)movieArray {
//deal with movieArray here
}

- (void)getMoviesFailed:(NSString *)failedMessage {
//deal with failure here
}

这未经过测试,但希望能为您提供合作路线图.

协议很好,因为你可以同时制作必需和可选的委托方法,它有助于改进你的帮助方法,使其在各个项目中变得非常可重用.如果您已实现协议但未实现协议所需的委托方法,编译器也会发出警告.如果您遵循此路径,请务必使用conformsToProtocol:和respondsToSelector:

Answer 2

从根本上说,正在发生的是你正在启动异步网络负载(异步是正确的方法,几乎​​可以肯定),然后你需要一些方法来恢复在加载开始之前你正在做的任何操作.你有几个选择:

• 创建自己的委托协议.然后,您的UITableViewController将自己设置为帮助程序的委托,并且帮助程序将调用helperDidLoad或者您为该方法命名的任何内容.有关在Cocoa编程指南中编写代理的更多信息.

• 使用块和继续传递样式.这有点先进,但我喜欢它.在你的UITableViewController中你会写这样的东西:

   [helper doSomething:^ (id loaded) { 
       [modelObject refresh:loaded]; // or whatever you need to do
   }];
  

  然后在你的助手中写下:

   - (void)doSomething:(void ^ (id))continuation {
       _continuation = continuation;
       //kick off network load
   }
  
  
   - (void)connectionDidFinishLoading:(NSURLConnection *)connection {
       _continuation(_data);
   }
  

• 使用通知.阅读NSNotificationCenter文档.
• 使用KVO.KVO编程指南有很多关于键值观察的好信息.