Question

So I had this code, and it did not work:

for (NSDictionary *item in data){
    [self.resultsArray addObject:item];
}

self.resultsArray is nil. But then I changed it to this:

NSMutableArray *myDataArray = [[NSMutableArray alloc] init];

for (NSDictionary *item in data){
    [myDataArray addObject:item];
}

self.resultsArray = myDataArray;
[myDataArray release];

and now it worked. self.resultsArray is now populated

So I’m a beginner in Objective C and I was wondering why can I not just directly use it in the property’s addObject. Why did I have to create another mutable array, populate it, assign it to the resultsArray property and release the mutable array I made?

Thanks in advance!

EDIT: Also, in a lot of books I’ve been working on, this is done a lot.

Answer 1

simple answer

You didn’t initialize self.resultArray before adding objects to it. It is just a pointer to the value which is nil until you alloc it.

self.resultArray = [[NSMutableArray alloc] init]; before adding objects to it will solve the issue.

However, this way of alloc’ing will create a memory leak, therefore it is not shown in books and examples. Memory leak can happen if the self.resultArray property is marked as retain and by calling alloc it will be retained 2 times.