从异步NSURLConnection/类返回NSDictionary

Question

我要做的是创建一个类，它在被调用时返回Json数据的NSDictionary。我在过去对图像做了同样的事情，但是我对如何用NSDictionary实现它有点困惑。

我想要做的是加载一个视图，然后在后台发送请求以获取一些Json数据(异步)，并返回包含要使用的数据的字典。我将在许多不同的视图中加载大量的Json数据，因此它应该是一个可重用的类。

- (id)initWithURL:(NSURL *)url
{
    self = [self init];

    if (self)
    {
        receivedData = [[NSMutableData alloc] init];
        [self loadWithURL:url];
    }

    return self;
}

- (void)loadWithURL:(NSURL *)url    
{
    NSURLConnection *connection = [NSURLConnection connectionWithRequest:[NSURLRequest requestWithURL:url]delegate:self];
    [connection start];
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    [receivedData setLength:0];
}

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

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

    NSError *error = nil;

    jsonReturn = [NSJSONSerialization JSONObjectWithData:receivedData options:kNilOptions error:&error];

}

我想过只是将结果添加到视图可以访问的协议中，但是必须有一种更简单/更干净的方法，对吧？有没有办法让它像这样返回NSdictionary：

NSDictionary *dictionary = LoadURLJSon initWithURL:myurl；

然后它就会找回NSDictionary？

Answer 1

您需要的是在异步API (具体地说，是[NSURLConnection start])之上的同步操作。如果没有一些繁重的线程杂耍，你就不能做到这一点，而且无论如何这都不是一个好主意--异步确实是个不错的选择。不要丢弃异步性。

执行一次性异步检索方法的最好方法是建立一个方法，该方法以URL、NSObject和选择器为参数，一旦请求完成，就在所述对象上调用所述选择器，并提供NSDictionary作为参数。这是Objective C进行回调的方式。

该方法将在内部实例化您的类，传递回调信息，并发起请求。一旦完成请求并将JSON解析成NSDictionary，您就可以在回调NSObject上调用[performSelector:]。

如果您最终想要同步操作，请使用[NSURLConnection sendSynchronousRequest]而不是[NSURLConnection start]。

Answer 2

这就是我最终得到的结果！这对将来路过这里的人应该是有用的。

 #import <Foundation/Foundation.h>

@protocol LoadJsonDelegate <NSObject, NSURLConnectionDelegate>
@optional
- (void) downloadFinished;
- (void) downloadReceivedData;
- (void) dataDownloadFailed: (NSString *) reason;
@end

@interface LoadURLJson : NSObject
{
    NSMutableData *receivedData;
    int expectedLength;
}

@property (nonatomic, strong) NSMutableData *receivedData;
@property (strong) NSString *urlString;
@property (weak) id <LoadJsonDelegate> delegate;

-(void)start;
-(void)cancel;

+ (id)download:(NSString *)aURLString withDelegate:(id <LoadJsonDelegate>)aDelegate;

@end

The .m

#import "LoadURLJson.h"
#define SAFE_PERFORM_WITH_ARG(THE_OBJECT, THE_SELECTOR, THE_ARG) (([THE_OBJECT respondsToSelector:THE_SELECTOR]) ? [THE_OBJECT performSelector:THE_SELECTOR withObject:THE_ARG] : nil)

@implementation LoadURLJson

@synthesize receivedData, delegate, urlString;

+ (id) download:(NSString *)aURLString withDelegate:(id <LoadJsonDelegate>)aDelegate
{
    if (!aURLString)
    {
        NSLog(@"Error. No URL string");
        return nil;
    }

    LoadURLJson *loadJson = [[self alloc] init];
    loadJson.urlString = aURLString;
    loadJson.delegate = aDelegate;
    [loadJson start];

    return loadJson;
}

-(void)start   
{
    receivedData = [NSMutableData data];
    NSURL *url = [NSURL URLWithString:urlString];

    NSURLConnection *connection = [NSURLConnection connectionWithRequest:[NSURLRequest requestWithURL:url]delegate:self];
    [connection start];
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    [receivedData setLength:0];

    // Check for bad connection
    expectedLength = [response expectedContentLength];
    if (expectedLength == NSURLResponseUnknownLength)
    {
        NSString *reason = [NSString stringWithFormat:@"Invalid URL [%@]", urlString];
        SAFE_PERFORM_WITH_ARG(delegate, @selector(dataDownloadFailed:), reason);
        [connection cancel];
        [self cleanup];
        return;
    }
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [receivedData appendData:data];
    SAFE_PERFORM_WITH_ARG(delegate, @selector(downloadReceivedData), nil);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    SAFE_PERFORM_WITH_ARG(delegate, @selector(downloadFinished), nil);
}

-(void)cleanup
{
    self.urlString = nil;
}

-(void)dealloc
{
    [self cleanup];
}

-(void)cancel
{
    [self cleanup];
}

@end

使用-在您的View.h中

#import "LoadURLJson.h"

@interface ViewController : UIViewController <LoadJsonDelegate>
{
    LoadURLJson *loadJson;
}

youView.m

通过以下方式进行呼叫：

loadJson = [LoadURLJson download:@"url" withDelegate:self];

然后实现

-(void)downloadFinished
{
    NSData *data = [[NSData alloc] initWithData:loadJson.receivedData];

    NSError *error = nil;
    NSDictionary *dictionary = [NSJSONSerialization JSONObjectWithData: data options: NSJSONReadingMutableContainers error:&error];

    NSLog(@"%@",dictionary);
}

基于这里的DownloadHelper：https://github.com/erica/iOS-5-Cookbook

BSD牌照。