Cocoa Touch:存取方法+内存需要澄清

Question

请考虑构造数组并将其返回到父对象的问题.请查看下面的代码和评论.

我的问题是:为什么方法三有效,而方法一和二没有？

// ****************************
// Master.m
// ****************************

// Simply declare array and call accessor
NSMutableArray * allElementTypes;
allElementTypes = [ElementObject badElements];




// ****************************
// ElementObject.m
// ****************************

// Doesn't work (EXE_BAD_ACCESS)
+ (NSMutableArray*) badElements {
    NSMutableArray * array = [[NSMutableArray alloc] initWithObjects:@"crab", @"poison", @"snake"];
    return array;
}

// Doesn't work (EXE_BAD_ACCESS)
+ (NSMutableArray*) badElements {
    return [NSMutableArray arrayWithObjects:@"crab", @"poison", @"snake"];
}

// WORKS
+ (NSMutableArray*) badElements {
    NSMutableArray * array = [[NSMutableArray alloc] init];
        [array addObject:@"crab"];
        [array addObject:@"poison"];
        [array addObject:@"snake"];

    return array;   // TODO: release this memory
}

Answer 1

-arrayWithObjects:或-initWithObjects采用nil终止,可变长度的参数列表.

你写了:

[NSMutableArray arrayWithObjects:@"crab", @"poison", @"snake"];

你应该写的地方:

[NSMutableArray arrayWithObjects:@"crab", @"poison", @"snake", nil];