Objective-C：为什么不调用指定的初始化器？答案

【问题标题】：Objective-C: Why not call the designated initializer?Objective-C：为什么不调用指定的初始化器？
【发布时间】：2015-02-26 10:39:59
【问题描述】：

我继承了这段代码：

- (id)initWithLocation:(CLLocation *)inLocation {
    if (self = [super init])
    {
        _location = [inLocation copy];
    }
    return self;
}

- (id)initWithLocation:(CLLocation *)inLocation offsetValue:(NSNumber *)offset {
    if (self = [super init])
    {
        _location = [inLocation copy];
        _offset = [offset copy];
    }
    return self;
}

我想知道第一个方法不调用指定的初始化程序是否有充分的理由（例如，像这样Is it okay to call an init method in self, in an init method?）？

即为什么不这样做：

- (id)initWithLocation:(CLLocation *)inLocation {
    if (self = [super init])
    {
        [self initWithLocation:inLocation offsetValue:nil];
    }
    return self;
}

- (id)initWithLocation:(CLLocation *)inLocation offsetValue:(NSNumber *)offset {
    if (self = [super init])
    {
        _location = [inLocation copy];
        _offset = [offset copy];
    }
    return self;
}

【问题讨论】：

标签： objective-c designated-initializer

【解决方案1】：

- (id)initWithLocation:(CLLocation *)inLocation offsetValue:(NSNumber *)offset 方法应该是一个指定的初始化器，- (id)initWithLocation:(CLLocation *)inLocation 应该这样调用它：

- (id)initWithLocation:(CLLocation *)inLocation {
    return [self initWithLocation:inLocation offsetValue:nil];
}

使用 NS_DESIGNATED_INITIALIZER 在类接口中标记指定的初始值设定项也是一种很好的做法：

- (id)initWithLocation:(CLLocation *)inLocation offsetValue:(NSNumber *)offset NS_DESIGNATED_INITIALIZER;

【讨论】：

鉴于答案都差不多，我选择了这个，因为它提到了 NS_DESIGNATED_INITIALIZER。

【解决方案2】：

更合适的方式是这样的：

- (id)initWithLocation:(CLLocation *)inLocation {
    return [self initWithLocation:inLocation offsetValue:nil];
}

- (id)initWithLocation:(CLLocation *)inLocation offsetValue:(NSNumber *)offset {
    if (self = [super init]) {
        _location = [inLocation copy];
        _offset = [offset copy];
    }
    return self;
}

【讨论】：

【解决方案3】：

你真正需要做的就是……

- (id)initWithLocation:(CLLocation *)inLocation {
    return [self initWithLocation:inLocation offsetValue:nil];
}

- (id)initWithLocation:(CLLocation *)inLocation offsetValue:(NSNumber *)offset {
    if (self = [super init])
    {
        _location = [inLocation copy];
        _offset = [offset copy];
    }
    return self;
}

你是对的。在这种情况下没有理由不这样做。

【讨论】：