目标C：NSMutableArray不保留对象

Question

I'm so stumped by this, I set the object in the array, but when I check it after they're all set, it comes up as (null)

for (int i = 0; i < [lines count]; i+=2) {
    [terms addObject:[lines objectAtIndex:i]];
    NSLog(@"%@",[terms objectAtIndex:i]);
}

Am I doing something wrong? terms is declared in the header, set as a property, and synthesized as an NSMutableArray

Answer 1

You have to first alloc and init the array before you use it. Setting the property makes it accessible outside the class and the synthesizer sets up the getter and setter but it doesn't alloc and init it.

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

Answer 2

"Synthesized as a NSMutableArray" - that's weird wording. In ObjC, @synthesize does not initialize variables - just generates a getter and a setter method. You still have to allocate the variable somehow - either by assigning to a property, or by setting the corresponding ivar directly. init is a nice place to do that.