如何获取远程文件上次修改日期 [英] How to get Remote File Last-Modification Date

问题描述

我需要获取远程文件的文件修改日期。

显然， 属性 返回 NULL ：

   - （BOOL）fileHasBeenModifiedSinceLastLaunch 
 {
 NSError * err = nil; 
 NSDictionary * attributes = [FILEMANAGER attributesOfItemAtPath：[NSURL URLWithString：@http://www.wrightscs.com/some_file.txt] error：& err]; 
 NSString * modified = [NSString stringWithFormat：@％@，[attributes objectForKey：@NSFileModificationDate]]; 
 NSString * savedmod = [[NSUserDefaults standardUserDefaults] objectForKey：@kFeedLastModified]; 
 
 NSLog（@Error：％@，[err localizedDescription]）; 
 NSLog（@Saved Modified Date：％@，savedmod）; 
 NSLog（@上次修改日期：％@，修改）; 
 
 [[NSUserDefaults standardUserDefaults] setObject：modified forKey：@kFeedLastModified]; 
 [[NSUserDefaults standardUserDefaults] synchronize]; 
 
 if（[savedmod isEqualToString：modified]）
 {
 NSLog（@文件尚未修改。 
 return NO; 
} else 
 {
 NSLog（@文件已修改。 
 return YES; 
} 
} 
  

输出：

b $ b

  2011-08-01 01：25：51.088 WrightsCS [2858：903]错误：无法打开文件some_file.txt，因为没有文件。 
 2011-08-01 01:25:51.092 WrightsCS [2858：903]保存的修改日期：（null）
 2011-08-01 01：25：51.093 WrightsCS [2858：903]上次修改日期：（null）
 2011-08-01 01：25：51.095 WrightsCS [2858：903] Feed没有被修改。 
  

解决方案

p>

您可以使用 NSURLConnection 和 NSURLRequest 的文件，那么您可以查找 Last-Modified 键：

   - （void） sendRequestForLastModifiedHeaders 
 {
 / *发送文件修改日期请求* / 
 NSURLRequest * modReq = [NSURLRequest requestWithURL：[NSURL URLWithString：@http://www.wrightscs.com/some_file .txt] 
 cachePolicy：NSURLRequestReloadIgnoringLocalCacheData timeoutInterval：60.0f]; 
 [[NSURLConnection alloc] initWithRequest：modReq delegate：self]; 
} 
  - （void）connection：（NSURLConnection *）connection didReceiveResponse：（NSURLResponse *）response 
 {
 / *将响应转换为NSHTTPURLResponse，
 allHeaderFields属性，然后获取
 Last-Modified键。 
 * / 
 NSString * last_modified = [NSString stringWithFormat：@％@，
 [[（NSHTTPURLResponse *）response allHeaderFields] objectForKey：@Last-Modified] 
 
 NSLog（@Last-Modified：％@，last_modified）; 
} 
  

I need to get the file modification date of a remote file.

Obviously, attributes in this example returns NULL:

- (BOOL) fileHasBeenModifiedSinceLastLaunch
{
    NSError * err = nil;
    NSDictionary * attributes = [FILEMANAGER attributesOfItemAtPath:[NSURL URLWithString:@"http://www.wrightscs.com/some_file.txt"] error:&err];
    NSString * modified = [NSString stringWithFormat:@"%@",[attributes objectForKey:@"NSFileModificationDate"]];
    NSString * savedmod = [[NSUserDefaults standardUserDefaults] objectForKey:@"kFeedLastModified"];

    NSLog(@"Error: %@",[err localizedDescription]);
    NSLog(@"Saved Modified Date: %@", savedmod);
    NSLog(@"Last  Modified Date: %@", modified);

    [[NSUserDefaults standardUserDefaults] setObject:modified forKey:@"kFeedLastModified"];
    [[NSUserDefaults standardUserDefaults] synchronize];

    if ( [savedmod isEqualToString:modified] )
    {
        NSLog(@"File has not been modified.");
        return NO; 
    } else 
    {
        NSLog(@"File has been modified.");
        return YES;
    }    
}

Output:

2011-08-01 01:25:51.088 WrightsCS[2858:903] Error: The file "some_file.txt" couldn’t be opened because there is no such file.
2011-08-01 01:25:51.092 WrightsCS[2858:903] Saved Modified Date: (null)
2011-08-01 01:25:51.093 WrightsCS[2858:903] Last  Modified Date: (null)
2011-08-01 01:25:51.095 WrightsCS[2858:903] Feed has not been modified.

解决方案

So I was able to figure it out.

You can use NSURLConnection and NSURLRequest to get the http headers of the file, then you can look for the key Last-Modified:

- (void) sendRequestForLastModifiedHeaders
{
    /*  send a request for file modification date  */
    NSURLRequest *modReq = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.wrightscs.com/some_file.txt"]
                                            cachePolicy:NSURLRequestReloadIgnoringLocalCacheData timeoutInterval:60.0f];
    [[NSURLConnection alloc] initWithRequest:modReq delegate:self];
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response 
{
    /*  convert response into an NSHTTPURLResponse, 
        call the allHeaderFields property, then get the
        Last-Modified key.
     */
    NSString * last_modified = [NSString stringWithFormat:@"%@",
                                                      [[(NSHTTPURLResponse *)response allHeaderFields] objectForKey:@"Last-Modified"]

    NSLog(@"Last-Modified: %@", last_modified );
} 

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