9.7. Delegate (Delegates) example

发布时间 ： 2025-10-25 13:32:32 UTC      

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Suppose object An invokes B to perform an operation, and once the operation is completed, object A must know that object B has completed the task and that object A will perform other necessary actions.

The key concepts in the above example are

  • An is the delegated object of B.

  • B refers to an A

  • A will implement B’s delegate method

  • B notify by entrusting method

Create a Delegates object

  1. Create an application with a single view

  2. Then select the file File-> New-> File…

addNewFile

  1. Then select Objective C and click next.

  2. Name the subclass of SampleProtocol NSObject, as follows

setProtocolName

  1. Then select create

6.向SampleProtocol.h文件夹中添加一种协议，然后更新代码，如下所示：

#import 
// 协议定义
@protocol SampleProtocolDelegate 
@required
- (void) processCompleted;
@end
// 协议定义结束
@interface SampleProtocol : NSObject

{
   // Delegate to respond back
   id  _delegate;

}
@property (nonatomic,strong) id delegate;

-(void)startSampleProcess; // Instance method

@end
   
 7.修改 SampleProtocol.m 文件代码，实现实例方法： 
 
 
 
#import "SampleProtocol.h"

@implementation SampleProtocol

-(void)startSampleProcess{

    [NSTimer scheduledTimerWithTimeInterval:3.0 target:self.delegate
    selector:@selector(processCompleted) userInfo:nil repeats:NO];
}
@end

 
 
 
 8. 将标签从对象库拖到UIView，从而在ViewController.xib中添加UILabel，如下所示: 
 
  delegateLabel  
 
 9. 创建一个IBOutlet标签并命名为myLabel，然后按如下所示更新代码并在ViewController.h里显示SampleProtocolDelegate 
 
 
 
#import 
#import "SampleProtocol.h"

@interface ViewController : UIViewController<SampleProtocolDelegate>
{
    IBOutlet UILabel *myLabel;
}
@end
   
 10. 完成授权方法，为SampleProtocol创建对象和调用startSampleProcess方法。如下所示，更新ViewController.m文件 
 
 
 
#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    SampleProtocol *sampleProtocol = [[SampleProtocol alloc]init];
    sampleProtocol.delegate = self;
    [myLabel setText:@"Processing..."];
    [sampleProtocol startSampleProcess];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Sample protocol delegate
-(void)processCompleted{
    [myLabel setText:@"Process Completed"];
}


@end

 
 
 
 11. 将看到如下所示的输出结果，最初的标签也会继续运行，一旦授权方法被SampleProtocol对象所调用，标签运行程序的代码也会更新。 
 
  delegateResult  
  
                    
                
                

                    

                        

                            
                                文章链接
                            
                            ：
                            9.7. Delegate (Delegates) example 
                        

                    

                

            
        
        

            

    
        

            

                

                    
                        
                        
                            
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