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
Create an application with a single view
Then select the file File-> New-> File…
Then select Objective C and click next.
Name the subclass of SampleProtocol NSObject, as follows
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 <Foundation/Foundation.h>
// 协议定义
@protocol SampleProtocolDelegate <NSObject>
@required
- (void) processCompleted;
@end
// 协议定义结束
@interface SampleProtocol : NSObject
{
// Delegate to respond back
id <SampleProtocolDelegate> _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:
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 <UIKit/UIKit.h>
#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。
