Question

How can I compare two NSArrays so that I can delete everything that isn’t in both arrays.

I tried it like this:

    NSArray *array1 = [NSArray arrayWithObjects:@"1",@"2",@"3",@"4", nil]; 
    NSArray *array2 = [NSArray arrayWithObjects:@"1",@"2",@"5",@"6", nil];

    NSMutableArray *myMutableArray = [NSMutableArray arrayWithArray:array1];
    NSMutableArray *myMutableArrayTwo = [myMutableArray copy];
    [myMutableArray removeObjectsInArray:array2];

    [array1 release];
    [array2 release];

    NSArray *array3 = [myMutableArray copy];
    [myMutableArrayTwo removeObjectsInArray:array3]; // Error here: "SIGABRT"

    NSLog(@"array3:%@",myMutableArrayTwo);

But it doesn’t work because of the error. It sais: “-[__NSArrayI removeObjectsInArray:]: unrecognized selector sent to instance 0x4e51550”

What did I do wrong? Or are there easier ways to solve my problem?
Thanks for the help

Answer 1

This is because you create a copy (non-mutable) of a NSMutableArray, so you are losing the mutable capabilities.

Use the mutableCopy method instead.

By the way, you’ve got huge memory problems. Your array1 and array2 variables are auto-released objects. Releasing them will lead you to problems.

You only need to release the arrays you created with alloc, copy or mutableCopy.