Objective C:委托(Delegates)示例
编辑:浏览器知识假设对象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…
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
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 <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。
文章TAG:objective 委托 delegate 示例 Objective加载全部内容