如何知道文件是通过NSFileManager编写的

Question

I got a problem , How to know the file is accessible ???

For example , the file is writing , but not finish yet. And I check the file again ,

I use

[[NSFileManager defaultManager] fileExistsAtPath:filePath]; 

It return true ... but the file is not accessible .

How to determine the file is ready ?

Thanks

Webber

EDIT Maybe I'm not telling my problem clearly . I mean if you start transport a video file . before transport finish . the video file is not accessible , but you still can get a part of transporting file.

Answer 1

Write Data in async way using GCD concept and once it is completed, the completion handler will be executed.(Where completion of a writing process shall be detected)

The dispatch I/O convenience API lets you perform asynchronous read and write operations on file descriptors. This API supports stream-based semantics for accessing the contents of the file-descriptor.

Method:

void dispatch_write ( dispatch_fd_t fd, dispatch_data_t data, dispatch_queue_t queue, void (^handler)(dispatch_data_t data, int error) );

Ref: https://developer.apple.com/library/ios/documentation/Performance/Reference/GCD_libdispatch_Ref/index.html#//apple_ref/c/func/dispatch_write

Answer 2

Basically you need to check the attributes of the file and particullary the NSFileBusy attribute:

if ([fileManager fileExistsAtPath:filePath]) {
    NSDictionary *attributes = [fileManager attributesOfItemAtPath:filePath error:nil];
    NSLog(@"File Busy %@", [attributes objectForKey:NSFileBusy]);
}

Answer 3

NSFileCoordinator and NSFilePresenter are created just for that. You may find interesting Advanced iCloud Document Storage video from wwdc that covers the usage of this classes. Building a Document-based App will be great to watch too.

Answer 4

Try to fetch data of file by using following code :

NSURL *url = [NSURL fileURLWithPath:filePath];
NSData *readData = [NSData dataWithContentsOfURL:url];