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Objective-C 代表：有另一个我称之为解析 XML 的类。需要知道何时在外部完成

发布于 2024-08-14 05:10:27 字数 123 浏览 5 评论 0原文

我有一个类调用另一个类来从 URL 解析 (NSXMLParse)。现在我想让调用这个类的类知道它何时完成，以便我可以填充 UI。我猜委派是一种可行的方法，但我从未与委派合作过，并且需要一些关于如何连接的指导。

谢谢

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︶葆Ⅱㄣ 2024-08-21 05:10:27

在我看来，NSNotification 是设置此类内容的最简单方法。

这是我的一个应用程序中的一个小片段：

在 method.m 中，当我正在处理的内容在类中完成时

[[NSNotificationCenter defaultCenter] postNotificationName:@"GlobalTagsReady" object:nil];

，以处理通知，

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(getTags) name:@"GlobalTagsReady" object:nil];

其中 @selector(getTags) 是方法称为

NSNotification is, in my opinion, the easiest way to setup something like this.

This is a small snippet from one of my apps:

in method.m when the something I'm processing has finished

[[NSNotificationCenter defaultCenter] postNotificationName:@"GlobalTagsReady" object:nil];

in the class to take care of the notification

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(getTags) name:@"GlobalTagsReady" object:nil];

where @selector(getTags) is the method to be called

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奶气 2024-08-21 05:10:27

基本上，委托只是意味着给一个对象一个指向它需要告诉它正在做什么的东西的指针。在 Cocoa 中，这通常是通过“协议”来处理的，这有点与接口声明相反：它们描述了一个对象将在另一个“实现”协议的对象上调用什么方法。严格来说，它们并不是必需的，尤其是在像这样的简单情况下，但它们是很好的实践，并且如果您要编写模块化代码，了解它们是一件好事。

在解析类的标头中：

 // This is the protocol declaration; anything implementing the "ParsingDelegate" protocol needs to have any method signatures listed herein
 @protocol ParsingDelegate
 - (void)parsingDidEndWithResult:(NSDictionary *)result
 @end

 @interface ParsingClass : NSObjectOrWhatever
 {
      ...
      id<ParsingDelegate> _delegate;
 }
 ...
 // We'll use this property to tell this object where to send its messages
 @property(nonatomic,assign) id<ParsingDelegate> delegate;
 @end

在解析器的实现中：

 @implementation ParsingClass
 @synthesize delegate=_delegate;
 // the "=_delegate" bit isn't necessary if you've named the instance variable without the underscore
 ...

在解析器完成其工作的方法中：

 ...
 // make sure the delegate object responds to it
 // assigning an object that doesn't conform to the delegate is a warning, not an error,
 // but it'll throw a runtime exception if you call the method
 if(self.delegate && [self.delegate respondsToSelector:@selector(parsingDidEndWithResult:)])
 {
      [self.delegate performSelector:@selector(parsingDidEndWithResult:) withObject:someResultObject];
 }
 ...

在 UI 类的标头中：

 @interface SomeUIClass : NSObjectOrWhatever <ParsingDelegate>

在 UI 类中，无论它在何处设置解析器，

 parser.delegate = self;

只需实现 -parsingDidEndWithResult： UI 类上的 方法。如果您同时运行多个解析器，您可能希望扩展委托方法以传入解析器对象本身（这是 Cocoa 标准），但对于您所描述的情况，这应该可以解决问题。

Basically, delegation just means giving an object a pointer back to something that it needs to tell about what it's doing. In Cocoa, this is usually handled through “protocols”, which are sort of the reverse of an interface declaration: they describe what methods an object will call on another object that “implements” the protocol. They're not, strictly speaking, necessary, particularly in a simple situation like this, but they're good practice and a good thing to know if you're going to be writing modular code.

In the parsing class's header:

 // This is the protocol declaration; anything implementing the "ParsingDelegate" protocol needs to have any method signatures listed herein
 @protocol ParsingDelegate
 - (void)parsingDidEndWithResult:(NSDictionary *)result
 @end

 @interface ParsingClass : NSObjectOrWhatever
 {
      ...
      id<ParsingDelegate> _delegate;
 }
 ...
 // We'll use this property to tell this object where to send its messages
 @property(nonatomic,assign) id<ParsingDelegate> delegate;
 @end

In the parser's implementation:

 @implementation ParsingClass
 @synthesize delegate=_delegate;
 // the "=_delegate" bit isn't necessary if you've named the instance variable without the underscore
 ...

In the method in which the parser finishes its stuff:

 ...
 // make sure the delegate object responds to it
 // assigning an object that doesn't conform to the delegate is a warning, not an error,
 // but it'll throw a runtime exception if you call the method
 if(self.delegate && [self.delegate respondsToSelector:@selector(parsingDidEndWithResult:)])
 {
      [self.delegate performSelector:@selector(parsingDidEndWithResult:) withObject:someResultObject];
 }
 ...

In the UI class's header:

 @interface SomeUIClass : NSObjectOrWhatever <ParsingDelegate>

In the UI class, wherever it sets up the parser,

 parser.delegate = self;

then just implement the -parsingDidEndWithResult: method on the UI class. If you have multiple parsers running at once, you might want to extend the delegate method to pass in the parser object itself—that's kind of the Cocoa standard—but for the case you've described, this should do the trick.

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