User Interface hangs when parsing

[JJSaccolo]

Hi everyone!
i'm sorry for my bad english, i'm not sure to use the correct verbs and pronouns!

So: my app has a UITableView and a button "reload".
Touching the button "reload" it starts to parse an xml file, that contains the data that i need to put in the tableview.

the xml is similar like this:

<abcs>
<abc id="001" label="hello" />
<abc id="002" label="ciao" />
...
</abcs>

i'm using TBXML and this is how it works: i created two NSMutableArray (id and label), and i add the data into the arrays.
So, at the end of the parse, i have this arrays:
id[0] = "001"
id[1] = "002"
...
label[0] = "hello"
label[1] = "ciao"

This is useful because when the user touch a line of the UITableView, i know what data read! If the user touch the line 0, i need to read id[0] and label[0].
After the parse i call the method "reloadData" for the tableview.

What's the problem?
That during the parse, the User Interface is blocked!
For example i've insert this

[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;

and, at the end, this

[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;

it appears only for a moment (at the end).

Why? what i'm doing wrong?
NB: i'm using the "NSUserDefaults" for save my arrays, so the user can read the data offline!

this is my code:

-(void)viewDidLoad{
NSString *save = [[NSUserDefaults standardUserDefaults] objectForKey:@"save"];
	if (!save){
		id = [[NSMutableArray alloc] init];
		label = [[NSMutableArray alloc] init];
	}
    else{
		id = [[NSUserDefaults standardUserDefaults] objectForKey:@"save_id"];
		label = [[NSUserDefaults standardUserDefaults] objectForKey:@"save_label"];
	}
}

//here the methods to load the tableview

-(IBAction)reload{
	[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
	
	NSURL *url = [NSURL URLWithString:@"URL_OF_THE_XML_FILE"];
        TBXML *tbxml_parse = [[TBXML alloc] initWithURL:url];
	if (tbxml_parse.rootXMLElement) {
		NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
		[defaults setObject:@"SI" forKey:@"save"];
		[self traverseElement:tbxml_parse.rootXMLElement];

//i save the arrays
		[defaults setObject:id forKey:@"save_id"];
		[defaults setObject:label forKey:@"save_label"];
                [mytableview reloadData];
		[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
		
		[tbxml_parse release];
              }
           else //UIAlertView "error, no connection"!
}


- (void) traverseElement:(TBXMLElement *)element {
	int sent_id = 0;
	int sent_label = 0;
        array_id = [[NSMutableArray alloc]init];
	array_label = [[NSMutableArray alloc]init];
do {
		TBXMLAttribute * attribute = element->firstAttribute;
		// if attribute is valid
		
		while (attribute) {
			
			NSString *xml_id = [NSString stringWithFormat:@"%@", [TBXML attributeName:attribute]];
			if ([xml_id isEqualToString:@"id"]){
				[array_id insertObject:[NSString stringWithFormat:@"%@", [TBXML attributeValue:attribute]] atIndex:sent_id];
				sent_id++;
			}
			NSString *xml_tipo = [NSString stringWithFormat:@"%@", [TBXML attributeName:attribute]];
			if ([xml_tipo isEqualToString:@"label"]){
				[array_tipo insertObject:[NSString stringWithFormat:@"%@", [TBXML attributeValue:attribute]] atIndex:sent_label];
				sent_label++;
			}
                      attribute = attribute->next;
}
		// if the element has child elements, process them
		if (element->firstChild)
            [self traverseElement:element->firstChild];
		// Obtain next sibling element
	} while ((element = element->nextSibling)); 
		
}

thank you

[JasonR]

You need to look through the documentation for TBXML to see how to load from a URL asynchronously. The method you are using makes the UI thread wait until the XML is loaded from the remote server.

[Esko2300]

I dident really look into all your code you posted but i think what you want to do is free the main thread of any type of parsing data so the user can respond to the program. all you have to do is look into grand central dispatch, this is how i did it with my program and now it moves flawlessly.

just follow these steps and this should work out for you
1)Create a queue to run your functions on
2)Call an asynchronous request of the q so it will run on its on thread, and your program will not have to wait for the funciton's to be done in order to continue, so your user can still interact with the program
3)update the UI with the main thread when you are done with parsing the data, call this line of code to update your new data to the UI. If you dont update the data on the main thread you have the possibility of having to wait a long time to see the results of your parsing

ex

-(void)parseData{
    1)
    dispatch_queue_t q = dispatch_queue_create("My Q",NULL);
    
   2)
   dispatch_async(q,^{
          [self parseMyData];

          3)
          dispatch_async(dispatch_get_main_queue(),^{
               [self updateUI];
          });
   )}: 
   dispatch_release(q);   
}

I hope this helps and heres the link to the GCD reference guide on apple

GCD Reference Guide

[jonusx]

You also probable don't want to use NSUserDefaults for saving data like that. Write the array to the filesystem. NSUserDefaults isn't intended for stuff like that