在 Objective-C 中定义和使用协议

发布于 2024-07-24 04:51:08 字数 781 浏览 6 评论 0原文

我正在尝试扩展 NSImageView，以便我可以将拖放责任委托给控制器。这一切都可以很好地解决编译器现在显示有关向具有类型 id 的对象发送消息的警告的一个问题。为了解决这个问题，我假设我只需在 ivar 的类型后面加上协议名称即可。但是，这会严重失败，并显示找不到协议定义的消息。

#import <Cocoa/Cocoa.h>


@interface DragDropImageView : NSImageView {
    id <DragDropImageViewDelegate> _delegate;
}

@property (readwrite, retain) id <DragDropImageViewDelegate> delegate;

@end

@protocol DragDropImageViewDelegate

@optional

- (NSDragOperation)dragDropImageView:(DragDropImageView *)ddiv validateDrop:(id     <NSDraggingInfo>)info;
- (BOOL)dragDropImageView:(DragDropImageView *)ddiv acceptDrop:(id <NSDraggingInfo>)info;
- (void)concludeDragOperation:(id <NSDraggingInfo>)sender;  

@end

有什么指示我可能会出错吗？我确信它一定很简单，但我对 obj-c 很陌生。

原文

I'm trying to extend NSImageView so I can delegate the drag/drop responsibility to the controller. It all works fine with the one problem that the compiler is now displaying warnings about sending messages to objects with type id. To solve this I assumed I would simply have to suffix the ivar's type with the name of the protocol. However, this fails miserably with the message that it cannot find the definition for the protocol.

#import <Cocoa/Cocoa.h>


@interface DragDropImageView : NSImageView {
    id <DragDropImageViewDelegate> _delegate;
}

@property (readwrite, retain) id <DragDropImageViewDelegate> delegate;

@end

@protocol DragDropImageViewDelegate

@optional

- (NSDragOperation)dragDropImageView:(DragDropImageView *)ddiv validateDrop:(id     <NSDraggingInfo>)info;
- (BOOL)dragDropImageView:(DragDropImageView *)ddiv acceptDrop:(id <NSDraggingInfo>)info;
- (void)concludeDragOperation:(id <NSDraggingInfo>)sender;  

@end

Any pointers where I might be going wrong? I'm sure it must be something simple, but I'm quite new to obj-c.

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晨曦慕雪 2024-07-31 04:51:08

你的方向是正确的，但你却被 C 编译器所困扰，它有点过时了。编译器令人窒息，因为协议的定义在您使用它时不可用。必须先定义 @protocol DragDropImageViewDelegate 才能使用 idDragDropImageViewDelegate> 作为一种类型。您可以将@protocol 定义移到使用之前（即在@interface 之前），或者

@protocol DragDropImageViewDelegate;

在@interface 之前添加一个（前向声明）并将@protocol 声明保留在原来的位置。

You're on the right track but you're getting hung up by the C compiler, which is a little archaic. The compiler is choking because the definition of the protocol is not available at the time you use it. @protocol DragDropImageViewDelegate must be defined before you can use id< DragDropImageViewDelegate> as a type. You can move the @protocol definition before the usage (i.e. before your @interface), or add a

@protocol DragDropImageViewDelegate;

before the @interface (a forward declaration) and leave the @protocol declaration where it is.

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我的影子我的梦 2024-07-31 04:51:08

作为一般规则，我首先定义协议，然后是

@class DragDropImageView;

但是您可以执行相反的操作并在前面定义：

@protocol DragDropImageViewDelegate;

在我看来，协议是声明的重要组成部分，并且往往很短，所以我更喜欢它首先，而不是迷失在头文件的底部，但它是一个品味问题。

As a general rule, I define the protocol first, preceeded by

@class DragDropImageView;

But you can do the reverse and preceed with:

@protocol DragDropImageViewDelegate;

To my mind, the protocol is an important part of the declaration, and tends to be quite short, so I prefer it to go first rather than be lost at the bottom of the header file, but its a matter of taste.

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