如何監視OS X上的文件更改？

Question

我希望得到寫入給定文件的通知 - 無需輪詢，不必讀取文件，也不必監視父目錄並觀察文件修改時間戳。我怎麼做？

Answer 1

我無法找到一個簡單的例子，所以我參與我想出了以供將來參考：

@interface FileWatch() 
@property(assign) dispatch_source_t source; 
@end 

@implementation FileWatch 
@synthesize source; 

- (id) initWithPath: (NSString*) path targetQueue: (dispatch_queue_t) queue block: (dispatch_block_t) handler 
{ 
    self = [super init]; 

    int descriptor = open([path fileSystemRepresentation], O_EVTONLY); 
    if (descriptor < 0) { 
     return nil; 
    } 

    [self setSource:dispatch_source_create(DISPATCH_SOURCE_TYPE_VNODE, descriptor, DISPATCH_VNODE_WRITE, queue)]; 
    dispatch_source_set_event_handler(source, handler); 
    dispatch_source_set_cancel_handler(source, ^{ 
     close(descriptor); 
    }); 

    dispatch_resume(source); 
    return self; 
} 

- (void) dealloc 
{ 
    if (source) { 
     dispatch_source_cancel(source); 
     dispatch_release(source); 
     source = NULL; 
    } 
} 

@end 

Answer 2

從我的實際經驗，在某些情況下，文件不僅被寫入但隨後被刪除重寫（一些plist文件的情況）。然後，您必須稍微調整代碼：在ordre中替換文件時再次調用該方法以保持監視。

- (void) myMonitoringMethodWithPath: :(NSString*) path 
     __block typeof(self) blockSelf = self; 
     __block dispatch_source_t source = dispatch_source_create(DISPATCH_SOURCE_TYPE_VNODE,fildes,             DISPATCH_VNODE_DELETE | DISPATCH_VNODE_WRITE | DISPATCH_VNODE_EXTEND | DISPATCH_VNODE_ATTRIB | DISPATCH_VNODE_LINK | DISPATCH_VNODE_RENAME | DISPATCH_VNODE_REVOKE, 
                    queue); 
    dispatch_source_set_event_handler(source,^
             { 
             unsigned long flags = dispatch_source_get_data(source); 
              //Do some stuff 

              if(flags & DISPATCH_VNODE_DELETE) 
              { 
               [blockSelf myMonitoringMethodWithPath:path]; 

              } 
             }); 
    dispatch_source_set_cancel_handler(source, ^(void) 
             { 
              close(fildes); 
             }); 
    dispatch_resume(source); 
}