Displaying file copy progress using FSCopyObjectAsync

It appears after much searching that there seems to be a common problem when trying to do a file copy and show a progress indicator relative to the amount of the file that has been copied. After spending some considerable time trying to resolve this issue, I find myself at the mercy of the StackOverflow Gods once again :-) - Hopefully one day I'll be among those that can help out the rookies too!

I am trying to get a progress bar to show the status of a copy process and once the copy process has finished, call a Cocoa method. The challenge - I need to make use of File Manager Carbon calls because NSFileManager does not give me the full ability I need.

I started out by trying to utilize the code on Matt Long's site Cocoa Is My Girlfriend. The code got me some good distance. I managed to get the file copy progress working. The bar updates and (with some additional searching within Apple docs) I found out how to tell if the file copy process has finished...

if (stage == kFSOperationStageComplete)

However, I have one last hurdle that is a little larger than my leap right now. I don't know how to pass an object reference into the callback and I don't know how to call a Cocoa method from the callback once finished. This is a limit of my Carbon -> Cocoa -> Carbon understanding. One of the comments on the blog said

"Instead of accessing the progress indicator via a static pointer, you can just use the void *info field of the FSFileOperationClientContext struct, and passing either the AppDelegate or the progress indicator itself."

Sounds like a great idea. Not sure how to do this. For the sake of everyone else that appears to bump into this issue and is coming from a non-Carbon background, based mostly upon the code from Matt's example, here is some simplified code as an example of the problem...

In a normal cocoa method:

CFRunLoopRef runLoop = CFRunLoopGetCurrent();
FSFileOperationRef fileOp = FSFileOperationCreate(kCFAllocatorDefault);

OSStatus status = FSFileOperationScheduleWithRunLoop(fileOp, 
                     runLoop, kCFRunLoopDefaultMode);

if (status) {
    NSLog(@"Failed to schedule operation with run loop: %@", status);
    return NO;
}

// Create a filesystem ref structure for the source and destination and 
// populate them with their respective paths from our NSTextFields.

FSRef source;
FSRef destination;

// Used FSPathMakeRefWithOptions instead of FSPathMakeRef which is in the 
// original example because I needed to use the kFSPathMakeRefDefaultOptions
// to deal with file paths to remote folders via a /Volume reference

FSPathMakeRefWithOptions((const UInt8 *)[aSource fileSystemRepresentation],
    kFSPathMakeRefDefaultOptions, 
    &source, 
    NULL);

Boolean isDir = true;

FSPathMakeRefWithOptions((const UInt8 *)[aDestDir fileSystemRepresentation],
    kFSPathMakeRefDefaultOptions, 
    &destination, 
    &isDir);

// Needed to change from the original to use CFStringRef so I could convert
// from an NSString (aDestFile) to a CFStringRef (targetFilename)

CFStringRef targetFilename = (CFStringRef)aDestFile;

// Start the async copy.

status = FSCopyObjectAsync (fileOp,
             &source,
             &destination, // Full path to destination dir
             targetFilename,
             kFSFileOperationDefaultOptions,
             statusCallback,
             1.0,
             NULL);

CFRelease(fileOp);

if (status) {

    NSString * errMsg = [NSString stringWithFormat:@"%@ - %@", 
                           [self class], status];

        NSLog(@"Failed to begin asynchronous object copy: %@", status);
}

Then the callback (in the same file)

static void statusCallback (FSFileOperationRef fileOp,
           const FSRef *currentItem,
           FSFileOperationStage stage,
           OSStatus error,
           CFDictionaryRef statusDictionary,
           void *info )
{

    NSLog(@"Callback got called.");

    // If the status dictionary is valid, we can grab the current values to 
    // display status changes, or in our case to update the progress indicator.

    if (statusDictionary)
    {

        CFNumberRef bytesCompleted;

        bytesCompleted = (CFNumberRef) CFDictionaryGetValue(statusDictionary,
                 kFSOperationBytesCompleteKey);

        CGFloat floatBytesCompleted;
        CFNumberGetValue (bytesCompleted, kCFNumberMaxType, 
                              &floatBytesCompleted);

        NSLog(@"Copied %d bytes so far.", 
                              (unsigned long long)floatBytesCompleted);

        // fileProgressIndicator is currently declared as a pointer to a 
        // static progress bar - but this needs to change so that it is a 
        // pointer passed in via the controller. Would like to have a 
        // pointer to an instance of a progress bar

        [fileProgressIndicator setDoubleValue:(double)floatBytesCompleted];
        [fileProgressIndicator displayIfNeeded];
     }

if (stage == kFSOperationStageComplete) {

    NSLog(@"Finished copying the file");

    // Would like to call a Cocoa Method here...
}

}

So the bottom line is how can I:

Pass a pointer to an instance of a progress bar from the calling method to the callback
Upon completion, call back out to a normal Cocoa method

And as always, help is much appreciated (and hopefully the answer will solve many of the issues and complaints I have seen in many threads!!)

You can do this by using the last parameter to FSCopyObjectAsync(), which is a struct of type FSFileOperationClientContext. One of the fields of that struct is info, which is a void* parameter that you can basically use as you see fit. Whatever you assign to that field of the struct you pass into FSCopyObjectAsync() will be passed in turn to your callback function as the last info function parameter there. A void* can be anything, including a pointer to an object, so you can use that to pass the instance of your object that you want to handle the callback.

The setup code would look like this:

FSFileOperationClientContext clientContext = {0}; //zero out the struct to begin with

clientContext.info = myProgressIndicator;
//All the other setup code
status = FSCopyObjectAsync (fileOp,
         &source,
         &destination, // Full path to destination dir
         targetFilename,
         kFSFileOperationDefaultOptions,
         statusCallback,
         1.0,
         &clientContext);

Then, in your callback function:

static void statusCallback (FSFileOperationRef fileOp,
       const FSRef *currentItem,
       FSFileOperationStage stage,
       OSStatus error,
       CFDictionaryRef statusDictionary,
       void *info )
{
    NSProgressIndicator* fileProgressIndicator = (NSProgressIndicator*)info;
    [fileProgressIndicator setDoubleValue:(double)floatBytesCompleted];
    [fileProgressIndicator displayIfNeeded];
}

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