NSURLConnection 有缓存吗？

Question

我正在使用最新的 SDK 和 XCode 4.2 为 iPad 开发 iOS 4 应用程序。

我的 JSON Web 服务有问题。如果某些数据已更改，我正在使用计时器每 3 秒检查一次。问题是数据发生了变化，但我在我的应用上看不到这些变化。

异步接收的数据始终相同。就像NSURLConnection 有一个缓存 或类似的东西，它总是返回它需要的第一个数据。

这是我的代码：

ControlPanelJSON.h

#import <Foundation/Foundation.h>
#import "SBJson.h"
#import "WebServiceDelegate.h"

@interface ControlPanelJSON : NSObject
{
    SBJsonParser* parser;
    NSURLRequest* request;
    NSMutableData* receivedData;

    BOOL isEncuestaVisible;
    BOOL isInfoVisible;
    BOOL isTwitterVisible;

    id<WebServiceDelegate> delegate;
}
@property (nonatomic, readonly) BOOL isEncuestaVisible;
@property (nonatomic, readonly) BOOL isInfoVisible;
@property (nonatomic, readonly) BOOL isTwitterVisible;

- (id) initWithWebServiceURLString:(NSString*)webServiceURL
                          delegate:(id<WebServiceDelegate>)del;

- (void)callWebService;

@end

ControlPanelJSON.m

#import "ControlPanelJSON.h"

#define kRootKey @"s"
#define kControlKey @"c"
#define kEstadoKey @"e"

#define kEncuestaTitle @"[ zzz ]"
#define kInfoTitle @"[ yyy ]"
#define kTwitterTitle @"[ xxx ]"

@implementation ControlPanelJSON

@synthesize isEncuestaVisible;
@synthesize isInfoVisible;
@synthesize isTwitterVisible;

- (id) initWithWebServiceURLString:(NSString*)webServiceURL
                          delegate:(id<WebServiceDelegate>)del
{
    if (self = [super init])
    {
        delegate = [del retain];
        request = [[NSURLRequest alloc] initWithURL: [NSURL URLWithString: webServiceURL]
                                        cachePolicy: NSURLCacheStorageNotAllowed
                                    timeoutInterval: 60.0];
        parser = [[SBJsonParser alloc] init];
    }
    return self;
}

- (void) dealloc
{
    [parser release];
    [request release];
    [receivedData release];

    [super dealloc];
}

- (void)callWebService
{
    NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:request delegate:self];
    if (theConnection)
    {
        // Create the NSMutableData to hold the received data.
        // receivedData is an instance variable declared elsewhere.
        receivedData = [[NSMutableData data] retain];
    }
    else
    {
        [delegate errorReceivedWithMessage:NSLocalizedString(@"CONNERROR", nil)];
    }
}

#pragma mark -
#pragma mark - NSURLConnectionDelegate

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    // This method is called when the server has determined that it
    // has enough information to create the NSURLResponse.

    // It can be called multiple times, for example in the case of a
    // redirect, so each time we reset the data.

    // Cuando se recibe este mensaje se debe descartar todo lo recibido anteriormente.
    [receivedData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    // Append the new data to receivedData.
    // receivedData is an instance variable declared elsewhere.
    [receivedData appendData:data];
}

- (void)connection:(NSURLConnection *)connection
  didFailWithError:(NSError *)error
{
    // release the connection, and the data object
    [connection release];
    // receivedData is declared as a method instance elsewhere
    [receivedData release];

    // inform the user
    [delegate errorReceivedWithMessage:
     [NSString stringWithFormat:@"Error - %@ %@",
      [error localizedDescription],
      [[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]]];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{   
    NSString *json_string = [[NSString alloc] initWithData:receivedData encoding:NSUTF8StringEncoding];
    NSDictionary* datos = [parser objectWithString:json_string error:nil]; // TODO: Otro error que manejar

    [connection release];
    //[receivedData release];
    //[parser release];
    [json_string release];

    NSArray* data = [datos objectForKey:kRootKey];
    for (int i = 0; i < data.count; i++)
    {
        NSDictionary* object = [data objectAtIndex:i];
        NSString* controlName = [object objectForKey:kControlKey];
        NSString* controlEstado = [object objectForKey:kEstadoKey];

        if ([controlName isEqualToString: kEncuestaTitle])
        {
            isEncuestaVisible = ([controlEstado isEqualToString: @"1"]);
            continue;
        }
        else if ([controlName isEqualToString: kInfoTitle])
        {
            isInfoVisible = ([controlEstado isEqualToString: @"1"]);
            continue;
        }
        else if ([controlName isEqualToString: kTwitterTitle])
        {
            isTwitterVisible = ([controlEstado isEqualToString: @"1"]);
            continue;
        }
    }

    [delegate dataReceived];
}

@end

在这行代码之后：

NSString *json_string = [[NSString alloc] initWithData:receivedData encoding:NSUTF8StringEncoding];

我添加了一个 NSLog，但我总是得到相同的 json_string

{"ctrls": [ { "control": "[ xxx ]","estado": "0" },{ "control": "[ yyy ]","estado": "0" },{ “控制”：“[zzz]”，“estado”：“0”}]}

有什么线索吗？

Answer 1

尝试在创建 NSURLRequest 时将缓存策略更改为：

NSURLRequestReloadIgnoringLocalAndRemoteCacheData

Answer 2

请使用：

NSURLRequestReloadIgnoringCacheData

请注意NSURLCacheStorageNotAllowed 是NSCachedURLResponse 类，而不是NSURLRequest。

根据NSURLRequest.h头文件，NSURLRequestReloadIgnoringLocalAndRemoteCacheData未实现如下图。

enum
{
    NSURLRequestUseProtocolCachePolicy = 0,

    NSURLRequestReloadIgnoringLocalCacheData = 1,
    NSURLRequestReloadIgnoringLocalAndRemoteCacheData = 4, // Unimplemented
    NSURLRequestReloadIgnoringCacheData = NSURLRequestReloadIgnoringLocalCacheData,

    NSURLRequestReturnCacheDataElseLoad = 2,
    NSURLRequestReturnCacheDataDontLoad = 3,

    NSURLRequestReloadRevalidatingCacheData = 5, // Unimplemented
};
typedef NSUInteger NSURLRequestCachePolicy;