NSFileHandle & Writing Asynch to a file in iOS - objective-c

Question

I have a situation that I receive a byte data through Web Services request and want to write it to a file on my iOS device. I used to append all data (till end of data) in a memory variable and at the end writing the data using NSStream to a file in my iOS device using method:
stream:(NSStream *)theStream handleEvent:(NSStreamEvent)streamEvent
It works fine for small size of data, but the problem is if I am receiving data via web services it could be a big chunk (couple MBs) and I don't want to collect all in memory to write it to the file, to make it efficent I think I have to switch to NSFileHandle to write data in a small chunk size to the same file in several times. Now my question is what is the best approach to do this? I mean how can I do write to the file in BACKGROUND using NSFileHandle? I use code like this:
- (void) setUpAsynchronousContentSave:(NSData *) data {
NSString *newFilePath = [NSHomeDirectory() stringByAppendingPathComponent:#"/Documents/MyFile.xml"];
if(![[NSFileManager defaultManager] fileExistsAtPath:newFilePath ]) {
[[NSFileManager defaultManager] createFileAtPath:newFilePath contents:nil attributes:nil];
}
if(!fileHandle_writer) {
fileHandle_writer = [NSFileHandle fileHandleForWritingAtPath:newFilePath];
}
[fileHandle_writer seekToEndOfFile];
[fileHandle_writer writeData:data];
}
but with passing a data size of 1-2 Mb to above method, do I need to make it running in background? FYI I'm writing in main thread.

Answer 1

Maybe you can try Grand Central Dispatch.
I spent some time trying it, bellow is my way to do it.
According to Apple's document, if our program need executing only one task at a time, we should create a "Serial Dispatch Queue".So, first declare a queue as iVar.
dispatch_queue_t queue;
create a serial dispatch queue in init or ViewDidLoad using
if(!queue)
{
queue = dispatch_queue_create("yourOwnQueueName", NULL);
}
When data occurs, call your method.
- (void) setUpAsynchronousContentSave:(NSData *) data {
NSString *newFilePath = [NSHomeDirectory() stringByAppendingPathComponent:#"/Documents/MyFile.xml"];
NSFileManager *fileManager = [[NSFileManager alloc] init];
if(![fileManager fileExistsAtPath:newFilePath ]) {
[fileManager createFileAtPath:newFilePath contents:nil attributes:nil];
}
if(!fileHandle_writer) {
self.fileHandle_writer = [NSFileHandle fileHandleForWritingAtPath:newFilePath];
}
dispatch_async( queue ,
^ {
// execute asynchronously
[fileHandle_writer seekToEndOfFile];
[fileHandle_writer writeData:data];
});
}
At last, we need to release the queue in ViewDidUnload or dealloc
if(queue)
{
dispatch_release(queue);
}
I combine these code with ASIHttp, and it works.
Hope it helps.