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可能重复:
Objective-C:类与实例方法？
方法C旁边的加号和减号是什么意思？

我试图环顾四周,无法得出一个可以解释我困惑的可靠答案.我已经看过几次,这是一个有一个方法的类,它的"方法类型"设置为"+"即:

-(Fraction*) fractionWithNumerator: (int) n denominator: (int) d;
现在怎么会有所不同
+(Fraction*) fractionWithNumerator: (int) n denominator: (int) d;

我正在尝试对一个看起来像这样的数组进行排序:(请忽略这些人已经过了任何生活年龄的事实!我只需要很多数字)

NSDictionary *person1 = [NSDictionary dictionaryWithObjectsAndKeys:@"sam",@"name",@"28.00",@"age",nil];
NSDictionary *person2 = [NSDictionary dictionaryWithObjectsAndKeys:@"cody",@"name",@"100.00",@"age",nil];
NSDictionary *person3 = [NSDictionary dictionaryWithObjectsAndKeys:@"marvin",@"name",@"299.00",@"age",nil];
NSDictionary *person4 = [NSDictionary dictionaryWithObjectsAndKeys:@"billy",@"name",@"0.0",@"age",nil];
NSDictionary *person5 = [NSDictionary dictionaryWithObjectsAndKeys:@"tammy",@"name",@"54.00",@"age",nil];

NSMutableArray *arr = [[NSMutableArray alloc] initWithObjects:person1,person2,person3,person4,person5,nil];

// before sort
NSLog(@"%@",arr);

NSSortDescriptor *ageSorter = [[NSSortDescriptor alloc] initWithKey:@"age" ascending:YES];
[arr sortUsingDescriptors:[NSArray arrayWithObject:ageSorter]];

// after sort
NSLog(@"%@",arr);

在排序之前,输出将是:

2010-07-21 10:46:31.898 Sorting[70673:207] (
    {
    age = "28.00";
    name = sam;
},
    {
    age = "100.00";
    name = cody;
},
    {
    age = "299.00";
    name = marvin;
},
    { …