iOS-委托(Delegates)

委托(Delegates)示例

假设对象A调用B来执行一项操作,操作一旦完成,对象A就必须知道对象B已完成任务且对象A将执行其他必要操作。

在上面的示例中的关键概念有

  • A是B的委托对象
  • B引用一个A
  • A将实现B的委托方法
  • B通过委托方法通知

创建一个委托(Delegates)对象

1. 创建一个单一视图的应用程序

2. 然后选择文件 File -> New -> File...

addNewFile

3. 然后选择Objective C单击下一步

4. 将SampleProtocol的子类命名为NSObject,如下所示

setProtocolName

5. 然后选择创建

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{ 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