NSProgressIndicator within the NSTableViewCell not update - objective-c

Question

There is a NSTableView which contains several cells. There are a NSTextField and NSProgressIndicator in the cell. Each cell has its own progress indicator which represent its own uploading percentage.
Now, I need to update the progress indicator according the uploading percentage so that we could know the progress of uploading.
- (void)startUploading:(NSArray *)filePathArray
{
if (self.QNToken) {
NSString *token = self.QNToken;
NSUInteger count = [filePathArray count];
// We may have multiple files to upload.
for (int i = 0; i < count; i ++) {
NSString *filePath = filePathArray[i];
NSData *fileData = [NSData dataWithContentsOfFile:filePath];
NSString *key = [fileData md5String];
// Upload option
QNUploadOption *option = [[QNUploadOption alloc] initWithMime:nil
progressHandler:^(NSString *key, float percent) {
QNUploadDetailCell *cell = [self.tableView viewAtColumn:0 row:i makeIfNecessary:NO];
[cell.progress.animator setDoubleValue:percent];
[cell.progress displayIfNeeded];
}
params:nil
checkCrc:NO
cancellationSignal:nil];
// Let's upload!
[self.uploadManager putFile:filePath
key:key
token:token
complete: ^(QNResponseInfo *info, NSString *key, NSDictionary *resp) {
NSLog(#"%#", info);
NSLog(#"%#", resp);
} option:option];
}
}
}
However, the progress indicator will never be animated.
I also print out the percent of the progressHandler: the percentage just keep increasing from 0 to 1.0
But the progress bar still keep stopping.
Any ideas?