我的代码的目的是比较服务器文件和本地文件的修改日期,如果服务器文件较新,它将下载它。
中的代码来使用同步请求但它没有奏效。 之后我一直在努力寻找解决方案,尝试异步请求,尝试了我在stackoverflow,google等周围找到的不同代码,但没有任何作用。
如果在终端我做curl -I <url-to-file>
我得到标题值,所以我知道这不是服务器问题。
这是我现在正在努力的代码(它是用Appdelegate.m编写的)
- (void)downloadFileIfUpdated {
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL: url
cachePolicy: NSURLRequestReloadIgnoringLocalCacheData
timeoutInterval: 10];
[request setHTTPMethod:@"HEAD"];
NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES];
if(!connection) {
NSLog(@"connection failed");
} else {
NSLog(@"connection succeeded");
}
}
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
[self downloadFileIfUpdated]
}
#pragma mark NSURLConnection delegate methods
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
NSString *lastModifiedString = nil;
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
if ([response respondsToSelector:@selector(allHeaderFields)]) {
lastModifiedString = [[response allHeaderFields] objectForKey:@"Last-Modified"];
}
[Here is where the formatting-date-code and downloading would take place]
}
现在,事实上,它给了我错误No visible @interface for 'NSURLResponse' declares de selector 'allHeaderFields'
。
当我使用同步方法时,错误是NSLog(@"%@",lastModifiedString)
返回(null)。
PS:如果有更好的方式我可以解释自己或代码,请告诉我。
更新
我使用的网址是ftp://
类型,这可能是我没有获得任何标题的问题。但我无法弄清楚如何做到这一点。
答案 0 :(得分:3)
将您的代码更改为此...在“if”条件中,您检查的是response
而不是httpResponse
:
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
NSString *lastModifiedString = nil;
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
if ([httpResponse respondsToSelector:@selector(allHeaderFields)]) {
lastModifiedString = [[httpResponse allHeaderFields] objectForKey:@"Last-Modified"];
}
// [Here is where the formatting-date-code and downloading would take place]
}
...一旦你觉得响应永远是NSHTTPURLResponse,你可能只是摆脱了条件语句:
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
NSString *lastModifiedString = [[httpResponse allHeaderFields] objectForKey:@"Last-Modified"];
// [Here is where the formatting-date-code and downloading would take place]
}