在界面生成器中使用Singleton? [英] Use Singleton In Interface Builder?

问题描述

我的单例设置如下:

static Universe *instance;

+ (Universe *)instance { return instance; }

+ (void)initialize
{
    static BOOL initialized = NO;
    if(!initialized)
    {
        initialized = YES;
        instance = [[Universe alloc] init];
    }
}

- (id) init
{
    self = [super init];
    if (self != nil) {
        self.showHistory = YES;
    }
    return self;
}

但是现在我意识到我想从Interface Builder实例化它.我当时想像这样切入init方法

but now I realize that I'd like to instantiate it from Interface Builder. I was thinking of just cutting into the init method like so

    if (instance) 
         return instance;

这是个坏主意吗?我希望IB来选择已经在+initialize方法中创建的实例.

is this a bad idea? I'd prefer IB to pick up the instance already created in the +initialize method.

推荐答案

这可以完成. Buck和Yachtman的可可设计模式中有关于这一部分的内容.

This can be done. There is a section about it in Cocoa Design Patterns by Buck and Yachtman.

根据您的情况，您可以执行以下操作:

In your case you could do something along the lines of:

static Universe *instance;

+ (Universe *)instance { return instance; }

+ (id)hiddenAlloc
{
  return [super alloc];
}

+ (id)alloc
{
  return [[self instance] retain];
}

+ (void)initialize
{
    static BOOL initialized = NO;
    if(!initialized)
    {
        initialized = YES;
        instance = [[Universe hiddenAlloc] init];
    }
}

- (id)init
{
  if(instance==nil) // allow only to be called once
  {
    // your normal initialization here
  }
  return self;
}

然后，笔尖加载代码将通过调用[[Universe alloc] init]正确拾取单例，并且您仍然可以像以前一样在代码中使用instance.

The nib loading code will then correctly pick up the singleton via its call to [[Universe alloc] init], and you can still use instance in your code as before.

这本书有更多详细信息，并建议实现new和allocWithZone(都简单地称为return [self alloc];)，以及错误报告存根以捕获copyWithZone和mutableCopyWithZone的尝试，以取得良好的效果.

The book has more detail and recommends implementing new and allocWithZone (both simply as return [self alloc];), plus error-reporting stubs to catch copyWithZone and mutableCopyWithZone attempts for good measure.

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