Initialize Array of Objects using NSArray

问题

I'm pretty new to Objective-C and iOS so I've been playing around with the Picker View. I've defined a Person Class so that when you create a new Person it automatically gives that person a name and age.

#import "Person.h"

@implementation Person

@synthesize personName, age;

-(id)init
{
    self = [super init];
    if(self)
    {
        personName = [self randomName];
        age = [self randomAge];
    }

    return self;
}

-(NSString *) randomName
{
    NSString* name;
    NSArray* nameArr = [NSArray arrayWithObjects: @"Jill Valentine", @"Peter Griffin", @"Meg Griffin", @"Jack Lolwut",
                            @"Mike Roflcoptor", @"Cindy Woods", @"Jessica Windmill", @"Alexander The Great",
                            @"Sarah Peterson", @"Scott Scottland", @"Geoff Fanta", @"Amanda Pope", @"Michael Meyers",
                            @"Richard Biggus", @"Montey Python", @"Mike Wut", @"Fake Person", @"Chair",
                            nil];
    NSUInteger randomIndex = arc4random() % [nameArr count];
    name = [nameArr objectAtIndex: randomIndex];
    return name;
}

-(NSInteger *) randomAge
{
    //lowerBound + arc4random() % (upperBound - lowerBound);
    NSInteger* num = (NSInteger*)(1 + arc4random() % (99 - 1));

    return num;
}

@end

Now I want to make an array of Persons so I can throw a bunch into the picker, pick one Person and show their age. First though I need to make an array of Persons. How do I make an array of objects, initialize and allocate them?

回答1:

NSMutableArray *persons = [NSMutableArray array];
for (int i = 0; i < myPersonsCount; i++) {
   [persons addObject:[[Person alloc] init]];
}
NSArray *arrayOfPersons = [NSArray arrayWithArray:persons]; // if you want immutable array

also you can reach this without using NSMutableArray:

NSArray *persons = [NSArray array];
for (int i = 0; i < myPersonsCount; i++) {
   persons = [persons arrayByAddingObject:[[Person alloc] init]];
}

One more thing - it's valid for ARC enabled environment, if you going to use it without ARC don't forget to add autoreleased objects into array!

[persons addObject:[[[Person alloc] init] autorelease];

回答2:

There is also a shorthand of doing this:

NSArray *persons = @[person1, person2, person3];

It's equivalent to

NSArray *persons = [NSArray arrayWithObjects:person1, person2, person3, nil];

As iiFreeman said, you still need to do proper memory management if you're not using ARC.

回答3:

No one commenting on the randomAge method?

This is so awfully wrong, it couldn't be any wronger.

NSInteger is a primitive type - it is most likely typedef'd as int or long. In the randomAge method, you calculate a number from about 1 to 98.

Then you can cast that number to an NSNumber. You had to add a cast because the compiler gave you a warning that you didn't understand. That made the warning go away, but left you with an awful bug: That number was forced to be a pointer, so now you have a pointer to an integer somewhere in the first 100 bytes of memory.

If you access an NSInteger through the pointer, your program will crash. If you write through the pointer, your program will crash. If you put it into an array or dictionary, your program will crash.

Change it either to NSInteger or int, which is probably the best, or to NSNumber if you need an object for some reason. Then create the object by calling [NSNumber numberWithInteger:99] or whatever number you want.

回答4:

This might not really answer the question, but just in case someone just need to quickly send a string value to a function that require a NSArray parameter.

NSArray *data = @[@"The String Value"];

if you need to send more than just 1 string value, you could also use

NSArray *data = @[@"The String Value", @"Second String", @"Third etc"];

then you can send it to the function like below

theFunction(data);

回答5:

This way you can Create NSArray, NSMutableArray.

NSArray keys =[NSArray arrayWithObjects:@"key1",@"key2",@"key3",nil];

NSArray objects =[NSArray arrayWithObjects:@"value1",@"value2",@"value3",nil];

来源：https://stackoverflow.com/questions/14970412/initialize-array-of-objects-using-nsarray

标签

ios

objective-c

arrays

nsarray