objective-c - 在实现中创建方法而不在标头中定义

Question

如何在类的@implementation 中创建一个方法而不在@interface 中定义它？

例如，我有一个构造函数，它进行一些初始化，然后从文件中读取数据。我想将文件读取代码分解为一个单独的方法，然后从构造函数中调用该方法。我不想在标头中定义这个方法，因为它只对这个@implementation 上下文是私有的。

这可能吗？

这是我的例子。我有一个从文件中读取 Todo 任务列表的小程序。

这是@interface：

@interface TDTaskList : NSObject {
  NSString* name; // The name of this list.
  NSMutableArray* tasks;  // The set of tasks in this list.
}

-(id)initListOfName:(NSString*)aName;
-(NSArray*)loadListWithName:(NSString*)aName;

@end

这是@implementation的一部分：

-(id)initListOfName:(NSString*)aName {
  if (self = [super init]) {
    name = aName;

    NSArray* aTasks = [self loadListWithName:aName];
    tasks = [NSMutableArray arrayWithArray:aTasks];
  }

  return self;
}

-(NSArray*)loadListWithName:(NSString*)aName {
  // TODO This is a STUB till i figure out how to read/write from a file ...

  TDTask* task1 = [[TDTask alloc] initWithLabel:@"Get the Milk."];
  TDTask* task2 = [[TDTask alloc] initWithLabel:@"Do some homework."];

  return [NSArray arrayWithObjects:task1, task2, nil];
}

我想要做的是不必在界面中定义以下内容：

-(NSArray*)loadListWithName:(NSString*)aName;

Answer 1

If you place the implementation of a method before any code that calls it you do not need to define it in the header.

So in this case put loadListWithName: in front of initListOfName: in the @implementation block and it will be good.

Note: Just because it is not defined in the header does not mean the method cannot be called by code outside of the object. Objective-C does not have private methods.

Answer 2

As Andy hinted in the comments, you can use Extensions (which look like a category without a name). The difference is that you must implement the methods declared in an extension whereas the compiler doesn't verify that you implement methods declared in a category.

.h:

@interface MyObject : NSObject
{
    NSNumber *number;
}
- (NSNumber *)number;
@end

.m:

@interface MyObject ()
- (void)setNumber:(NSNumber *)newNumber;
@end

@implementation MyObject

- (NSNumber *)number
{
    return number;
}
- (void)setNumber:(NSNumber *)newNumber
{
    number = newNumber;
}
@end

Answer 3

您可以使用类别：

// In TDTaskList.m
@interface TDTaskList(TDTaskListPrivate)
-(id)initListOfName:(NSString*)aName;
-(NSArray*)loadListWithName:(NSString*)aName;
@end

@implementation TDTaskList(TDTaskListPrivate)

// implementation of initListOfName and loadListWithName ...

@end

Answer 4

You have two reasonable options. Both were basically described already but IMHO were a bit unclear or even plain wrong.

Categories are not one of them as they are AFAIK meant for the entirely different purpose of breaking implementations into multiple source files.

Do as Nathan described above. Though he is wrong with his last assumption (private methods).

Use a private method extension definition to allow forward referencing as follows:

1. remove the definition of loadListWithName from your header entirely
2. add the following into the source (.m) before the @implementation block

@interface TDTaskList (PrivateMethods)
-(NSArray*)loadListWithName:(NSString*)aName;
@end

@implementation ...