Question

我正在尝试了解委托模式的工作原理。下面是我尝试过的一些代码，但问题是委托方法downloadStarted和downloadFinished永远不会被调用。

我想念的是什么？

DownloaderDelegate.h

@protocol DownloaderDelegate <NSObject>
-(void)downloadStarted;
-(void)downloadFinished;
@end

Downloader.h

#import "DownloaderDelegate.h"

@interface Downloader : NSObject 

@property (nonatomic, retain) id<DownloaderDelegate>delegate;
-(void)fileIsDownloaded;
-(void)downloadFile;
@end

Downloader.m

@implementation Downloader
@synthesize delegate = _delegate;


-(void)downloadFile
{
    [[self delegate] downloadStarted];

    [NSTimer timerWithTimeInterval:5 
                            target:self 
                            selector:@selector(fileIsDownloaded) 
                            userInfo:nil 
                            repeats:NO];
}


-(void)fileIsDownloaded
{
    [[self delegate]downloadFinished];
}
@end

AppDelegate.m

    - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
    {
        ....
        Downloader *d = [[Downloader alloc]init];
        [d downloadFile];
        [d release];
        ....
    }

-(void)downloadStarted
{
    NSLog(@"Started");
}

-(void)downloadFinished
{
    NSLog(@"Finished");
}

Answer 1

您的AppDelegate需要实施DownloaderDelegate协议：

@interface AppDelegate : NSObject <UIApplicationDelegate,DownloaderDelegate>

然后，当您实例化下载程序时，请将AppDelegate作为其委托。

d.delegate = self;

Answer 2

首先，您将代理的属性更改为“分配”，它不需要reatin。然后设置 d.delegate = self;（或您需要的类）。然后只有您可以访问该类的委托。在您需要委托的类的.h文件中，您必须包含委托例如：

@interface AppDelegate : NSObject<UIApplicationDelegate,DownloaderDelegate>

委托模式

2 个答案: