NSURLConnection 确实触发了didReceiveData，但是返回的数据为零

Question

其他问题： 现在接收到的总数据长度为 89973。但是使用下面的代码将其转换为字符串会返回一个（空）字符串。 已解决：将编码更改为 NSASCIIStringEncoding，现在可以使用了。

NSString *responseString = [[NSString alloc] initWithData:receivedData encoding:NSUTF8StringEncoding];
NSLog(@"Received string: %@", responseString);

已解决的问题： 我正在尝试登录网站并获取返回的数据。 一切正常，重定向工作正常。

didReceiveData 也被多次调用，但奇怪的是：数据长度为零。即使我从 didReceiveData 中 NSLog 数据长度。

下面是 .m 和 .h 文件以及生成的 NSLog 信息。

我对 Objective-C 还是很陌生，现在我正在尝试解决这个问题几个小时，但我似乎找不到原因。

希望有人能帮我看看。

这是.m文件

#import "SiteConnection.h"

@implementation SiteConnection

@synthesize username;
@synthesize password;

// Other
- (void) printInstanceVars {

}

- (void) getInformation {
    // Enable Network Indicator
    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];

    // Set the request URL
    url = [NSURL URLWithString:@"http://url.com"];

    // Create the request using the URL defined above
    NSMutableURLRequest * request = [NSMutableURLRequest requestWithURL:url];

    // Change User-Agent to a Browser
    [request setValue:@"Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:13.0) Gecko/20100101 Firefox/13.0.1" forHTTPHeaderField:@"User-Agent"];

    // Change method to POST
    [request setHTTPMethod:@"POST"];

    // Create POST string
    NSString *requestData = [NSString stringWithFormat:@"data=value"];

    // Append POST string to the request
    [request setHTTPBody: [requestData dataUsingEncoding:NSUTF8StringEncoding]];

    // Initialize the connection
    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];

    // Start the connection
    [connection start];
}

- (NSURLRequest *)connection:(NSURLConnection *)connection
         willSendRequest:(NSURLRequest *)request
        redirectResponse:(NSURLResponse *)response
{
    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
    int statusCode = [httpResponse statusCode];

    // http statuscodes between 300 & 400 is a redirect ...
    if (response && statusCode >= 300 && statusCode < 400) {
        NSLog(@"Redirecting to : %@ (%u)", [request URL], statusCode);
    }

    return request;
}

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

    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
    NSLog(@"Response: %u (%@)", [httpResponse statusCode], [NSHTTPURLResponse localizedStringForStatusCode:[httpResponse statusCode]]);
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    [receivedData appendData:data];
    NSLog(@"Receiving data... Length: %d", [receivedData length]);
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    NSLog(@"Error: %@", [error localizedDescription]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    // Hide Network Indicator
    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];

    // Display data length
    NSLog(@"Total received data: %d", [receivedData length]);

    // Convert data into string and display it
    NSString *responseString = [[NSString alloc] initWithData:receivedData encoding:NSUTF8StringEncoding];
    NSLog(@"Received string: %@", responseString);
    //NSLog(@"Cookies: %@", [[NSHTTPCookieStorage sharedHTTPCookieStorage] description]);
}

这是.h文件

#import <Foundation/Foundation.h>

@class StatusViewController;

@interface SiteConnection : NSObject {
    NSString *username;
    NSString *password;
    NSURL *url;
    NSMutableData *receivedData;
}

@property NSString *username;
@property NSString *password;

// Other
- (void) printInstanceVars;
- (void) getInformation;

@end

这是生成的 NSLog：

2012-07-02 15:41:12.578 Vodafone[25051:11303] Response: 200 (no error)
2012-07-02 15:41:12.578 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.580 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.580 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.582 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.583 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.585 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.586 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.587 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.590 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.590 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.591 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.592 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.596 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.601 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.605 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.608 Vodafone[25051:11303] Receiving data... Length: 0
2012-07-02 15:41:12.608 Vodafone[25051:11303] Total received data: 0
2012-07-02 15:41:12.608 Vodafone[25051:11303] Received string: 

Answer 1

这样做：

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    if (!receivedData)
    {
        receivedData = [NSMutableData data];
    }

    [receivedData appendData:data];

    NSLog(@"Receiving data... Length: %d", [receivedData length]);
}

Answer 2

看来你忘记了：

NSMutableData *receivedData = [[NSMutableData alloc] init];

Answer 3

在我看来你从未初始化receivedData。因此，您将收到的数据附加到一个 nil 指针，这显然没有效果；-) 在使用之前尝试receivedData = [[NSMutableData alloc] init]; 之类的内容。