NSMutableArray from NSArray

Question

i have the following code and i want to use NSMutable arrays instead of NSArray could you tell me how to load the NSMutable array, as the current method does not work.

-(void) whatever{
NSData *htmlData = [[NSString stringWithContentsOfURL:[NSURL URLWithString: @"http://www.objectgraph.com/contact.html"]] dataUsingEncoding:NSUTF8StringEncoding];
TFHpple *xpathParser = [[TFHpple alloc] initWithHTMLData:htmlData];
NSArray *titles  = [xpathParser search:@"//h3"]; // get the page title - this is xpath     notation
TFHppleElement *title = [titles objectAtIndex:0];
NSString *myTitles = [title content];

NSArray *articles  = [xpathParser search:@"//h4"]; // get the page article - this is xpath     notation
TFHppleElement *article = [articles objectAtIndex:0];
NSString *myArtical = [article content];

i have tried :

NSMutableArray *titles  = [xpathParser search:@"//h3"];

but it does load the values?

Solution 1

You can invoke mutableCopy on an NSArray object to return to you an NSMutableArray.

Note that the callee will obtain ownership of this object since the method name contains "copy".

(Apple's memory management guide states that a method name containing the words "alloc", "new" or "copy" should by convention return an object which you own, and as such must relinquish ownership of at some point.)

Solution 2

Simply like this:

NSArray* someArray = [xpathParser search:@"//h3"];
NSMutableArray* mutableArray = [someArray mutableCopy];

That's quite literally, it.

Solution 3

Assuming [xpathparser ...] returns an NSArray, you can use:

NSMutableArray *titles  = [NSMutableArray arrayWithArray:[xpathParser search:@"//h3"]];

Comments

[Nick Forge]

+[NSMutableArray arrayWithArray:] has the benefit of being autoreleased - if you use -[NSArray mutableCopy], you'll need to release/autorelease yourself.

[JeremyP]

I would up voted you but you wrote "should by convention return an object with a reference count = 1" which is technically wrong. In fact if you read your own link you'll see it doesn't even use the phrase "retain count" in the object ownership policy section.

[JeremyP]

You've missed the point. Apple's memory management guide says the convention is that you own the object. It's an implementation detail that the retain count is 1 (which isn't always true anyway).

[Basil Bourque]

Is comment by Nick Forge now irrelevant under ARC?

[James]

@BasilBourque no, some older but still maintained apps still use MRR

[jer]

I'd still recommend my way if you're using MRC, just make sure to do [[someArray mutableCopy] autorelease] instead if you want it autoreleased.