iOS 教程
iOS - 委托（Delegates）
委托（Delegates）示例
假設(shè)對(duì)象A調(diào)用B來(lái)執(zhí)行一項(xiàng)操作，操作一旦完成，對(duì)象A就必須知道對(duì)象B已完成任務(wù)且對(duì)象A將執(zhí)行其他必要操作。
在上面的示例中的關(guān)鍵概念有
- A是B的委托對(duì)象
- B引用一個(gè)A
- A將實(shí)現(xiàn)B的委托方法
- B通過(guò)委托方法通知
創(chuàng)建一個(gè)委托（Delegates）對(duì)象
1. 創(chuàng)建一個(gè)單一視圖的應(yīng)用程序
2. 然后選擇文件 File -> New -> File...
3. 然后選擇Objective C單擊下一步
4. 將SampleProtocol的子類命名為NSObject，如下所示
5. 然后選擇創(chuàng)建
6.向SampleProtocol.h文件夾中添加一種協(xié)議，然后更新代碼，如下所示：
#import <Foundation/Foundation.h>
// 協(xié)議定義
@protocol SampleProtocolDelegate <NSObject>
@required
- (void) processCompleted;
@end
// 協(xié)議定義結(jié)束
@interface SampleProtocol : NSObject
{
// Delegate to respond back
id <SampleProtocolDelegate> _delegate;
}
@property (nonatomic,strong) id delegate;
-(void)startSampleProcess; // Instance method
@end7.修改 SampleProtocol.m 文件代碼，實(shí)現(xiàn)實(shí)例方法：
#import "SampleProtocol.h"
@implementation SampleProtocol
-(void)startSampleProcess{
[NSTimer scheduledTimerWithTimeInterval:3.0 target:self.delegate
????selector:@selector(processCompleted) userInfo:nil repeats:NO];
}
@end8. 將標(biāo)簽從對(duì)象庫(kù)拖到UIView，從而在ViewController.xib中添加UILabel，如下所示:
9. 創(chuàng)建一個(gè)IBOutlet標(biāo)簽并命名為myLabel，然后按如下所示更新代碼并在ViewController.h里顯示SampleProtocolDelegate
#import <UIKit/UIKit.h>
#import "SampleProtocol.h"
@interface ViewController : UIViewController<SampleProtocolDelegate>
{
IBOutlet UILabel *myLabel;
}
@end10. 完成授權(quán)方法，為SampleProtocol創(chuàng)建對(duì)象和調(diào)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"];
}
@end11. 將看到如下所示的輸出結(jié)果，最初的標(biāo)簽也會(huì)繼續(xù)運(yùn)行，一旦授權(quán)方法被SampleProtocol對(duì)象所調(diào)用，標(biāo)簽運(yùn)行程序的代碼也會(huì)更新。
