如何在Objective-C中的视图控制器之间传递对象？ [英] How do you pass objects between View Controllers in Objective-C?

问题描述

我一直在跋涉一些代码两天，试图找出为什么我无法获取我在.h中声明并在.m中实现并在viewDidLoad函数中设置的全局NSMutableArray变量。

I've been trudging through some code for two days trying to figure out why I couldn't fetch a global NSMutableArray variable I declared in the .h and implemented in .m and set in a the viewDidLoad function.

我终于明白了：在Ob​​jective-C中没有全局变量这样的东西，至少在PHP意义上我不知道。我从未真正阅读过XCode错误警告，但即使不是很简单的英语也是如此：在类方法中访问实例变量'blah'。

It finally dawned on me: there's no such thing as a global variable in Objective-C, at least not in the PHP sense I've come to know. I didn't ever really read the XCode error warnings, but there it was, even if not quite plain English: "Instance variable 'blah' accessed in class method."

我的问题：我现在该怎么办？我有两个View Controller需要访问我通过URL从JSON文件生成的中央NSMutableDictionary。它基本上是我所有Table View钻取的扩展菜单，我想要其他几个全局（非静态）变量。

My question: What am I supposed to do now? I've got two View Controllers that need to access a central NSMutableDictionary I generate from a JSON file via URL. It's basically an extended menu for all my Table View drill downs, and I'd like to have couple other "global" (non-static) variables.

我有吗每次我想生成这个NSMutableDictionary时抓取JSON还是有一些方法可以设置它一次并通过#import从各个类访问它？我是否必须将数据写入文件，或者人们通常会采用其他方式吗？

Do I have to grab the JSON each time I want to generate this NSMutableDictionary or is there some way to set it once and access it from various classes via #import? Do I have to write data to a file, or is there another way people usually do this?

推荐答案

如果您有两个视图访问共享NSMutableDictionary的控制器，你可以将指向公共字典的指针传递到它们各自的初始化消息吗？

If you have two view controllers that access the shared NSMutableDictionary, can you pass a pointer to the common dictionary into their respective init messages?

所以在你的AppDelegate中：

So in your AppDelegate:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{
  // the app delegate doesn't keep a reference this, it just passes it to the 
  // view controllers who retain the data (and it goes away when both have been released)
  NSMutableDictionary * commonData = [[NSMutableDictionary new] autorelease];

  // some method to parse the JSON and build the dictionary
  [self populateDataFromJSON:commonData];

   // each view controller retains the pointer to NSMutableDictionary (and releases it on dealloc)
   self.m_viewControllerOne = [[[UIViewControllerOne alloc] initWithData:commonData] autorelease];
   self.m_viewControllerTwo = [[[UIViewControllerTwo alloc] initWithData:commonData] autorelease];
}

在各自的UIViewControllerOne和UIViewControllerTwo实现中

And in your respective UIViewControllerOne and UIViewControllerTwo implementations

- (id)initWithData:(NSMutableDictionary*)data
{
    // call the base class ini
    if (!(self=[super init]))
        return nil;

    // set your retained property
    self.sharedData = data;
}

// don't forget to release the property
- (void)dealloc {
    [sharedData release];
    [super dealloc];
}

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