iPhone-抽象类的初始化方法

本文介绍了iPhone-抽象类的初始化方法的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我想创建具有以下属性的汽车，车辆和飞机类：

I want to create classes Car, Vehicle, and Airplane with the following properties:

汽车和飞机都是Vehicle的子类。

汽车和飞机都具有initWithString方法。

汽车和飞机的initWithString方法可接受的输入字符串不重叠。

车辆是几乎抽象的，从某种意义上说，任何初始化的实例都应该是汽车或飞机。

可以将字符串传递给Vehicle和根据输入字符串返回Car实例，飞机实例或nil实例。

Car and Airplane are both subclasses of Vehicle.
Car and Airplane both have an initWithString method.
The acceptable input strings for Car's and Airplane's initWithString methods do not overlap.
Vehicle is "almost abstract", in the sense that any initialized instance should be either a Car or an Airplane.
It is possible to pass a string into Vehicle and get back an instance of Car, an instance of Airplane, or nil, depending on the input string.

任何特殊的设计模式我都应该喜欢吗？特别是对于Vehicle的initWithString和/或newVehicleWithString方法。

Any particular design pattern I should prefer? In particular for Vehicle's initWithString and/or newVehicleWithString methods.

推荐答案

您需要的是类集群模式。您的 Vehicle initWithString：方法可能类似于：

What you need is the "class cluster" pattern. Your Vehicle initWithString: method could look something like this:

- (id) initWithString:(NSString *)mode {
  // note that we don't call [super init] in a class cluster. 
  // instead, we have to release self because it's an unwanted Vehicle instance
  [self release];
  if([mode isEqualToString:@"wheels"]) {
    return [[Car alloc] initWithString:@"wheels"];
  }
  if([mode isEqualToString:@"wings"]) {
    return [[Airplane alloc] initWithString:@"wings"];
  }
  return nil;  //alternately, raise NSInvalidArgumentException
}

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