CODEWITHSUNDEEP
iphoneobjective-cmultithreadingxcode
Jon
Jon

Reputation: 4732

Can I use a background thread to parse data?

I'm using chcsvparser to parse data from a csv file on my apps launch. It's taking way too long to startup on main thread so I was thinking of doing this on the background thread. But I read that you can't pass objects between the threads. The parser outputs an NSArray so is there a way to do this? I've also read that you shouldn't change UI from background thread but this array will load a table view.

Upvotes: 1

Views: 4201

Answers (4)

Joze
Joze

Reputation: 668

It is better to use NSOperation class to do that job. You can find a nice example named "LazyTableImages" at XCode documentation. It is uses a NSOperation to parse a XML

Upvotes: 0

DShah
DShah

Reputation: 9876

ofcourse we can pass objects to thread... please go through the link which shows how to process heavy task in background...

Upvotes: 0

ArunGJ
ArunGJ

Reputation: 2683

You can always pass objects between threads.

Use the following code to create a thread and pass the object to it.

[NSThread detachNewThreadSelector:@selector(myThreadSelector:) toTarget:self withObject:myObject];

After the thread function is over you can pass the data back to the main thread using 

[self performSelectorOnMainThread:@selector(myMainSelector:) withObject:myReturnObject waitUntilDone:NO];

you can pass the output NSArray from the parser to myMainSelector: and reload the tableview in it.

-(void)myMainSelector:(id)sender
{
    NSArray *arr = sender;
    tableDataArray = [NSArray arrayWithArray:arr];
    [yourTableView reloadData];
}

You can show an activity indicator while you are in the thread method.

Upvotes: 8

csano
csano

Reputation: 13696

The NSObject class has several different instance methods that allow you to invoke methods on the main UI thread. The performSelectorOnMainThread:withObject:waitUntilDone: method, for instance, allows you to invoke a method of the receiver on the main thread with the object of your choice.

Here's some code to get you started:

-(void) dataDoneLoading:(id) obj {
    NSMutableArray *array = (NSMutableArray *) obj;
    // update your UI
    NSLog(@"done");
}

-(void) myThread:(id) obj {
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    NSMutableArray *array = [[[NSMutableArray alloc]init ]autorelease];

    // build up your array

    [self performSelectorOnMainThread:@selector(dataDoneLoading:) withObject:array waitUntilDone:NO];

    [pool release];    
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    [NSThread detachNewThreadSelector:@selector(myThread:) toTarget:self withObject:nil];    
}

Upvotes: 2

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