这是创建自己的委托的基本概念。

委托非常有用，可以手动控制应用程序中视图控制器数组之间的传递。使用委托可以很好地管理控制流。

这里是自己委托的一个小例子....

1. 创建一个协议类....（仅.h文件）

SampleDelegate.h

#import
@protocol SampleDelegate
@optional
#pragma Home Delegate
-(NSString *)getViewName;
@end

1. 在想要将另一个类的委托的类中导入上述协议类。在我的示例中，我使用AppDelegate将其委托为HomeViewController的对象。

还要在Delegate Reference中添加上述DelegateName。

ownDelegateAppDelegate.h

#import "SampleDelegate.h"
@interface ownDelegateAppDelegate : NSObject  {
}

ownDelegateAppDelegate.m

//setDelegate of the HomeViewController's object as
[homeViewControllerObject setDelegate:self];
//add this delegate method definition
-(NSString *)getViewName
{
    return @"Delegate Called";
}

HomeViewController.h

#import
#import "SampleDelegate.h"
@interface HomeViewController : UIViewController {
    iddelegate;
}
@property(readwrite , assign) iddelegate;
@end

HomeViewController.h

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    UILabel *lblTitle = [[UILabel alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    lblTitle.text = [delegate getViewName];
    lblTitle.textAlignment = UITextAlignmentCenter;
    [self.view addSubview:lblTitle];
}

首先定义一个代理，如下所示 -

@protocol IconDownloaderDelegate;

然后创建一个代理对象，如下所示 -

@interface IconDownloader : NSObject
{
    NSIndexPath *indexPathInTableView;
    id  delegate;
    NSMutableData *activeDownload;
    NSURLConnection *imageConnection;
}

为其声明一个属性 -

@property (nonatomic, assign) id  delegate;

定义它 -

@protocol IconDownloaderDelegate 
- (void)appImageDidLoad:(NSIndexPath *)indexPath;
@end

然后你可以在这个代理上调用方法 -

[delegate appImageDidLoad:self.indexPathInTableView];

这是图像下载器类的完整源代码 -

.h 文件 -

@class AppRecord;
@class RootViewController;
@protocol IconDownloaderDelegate;
@interface IconDownloader : NSObject
{
    AppRecord *appRecord;
    NSIndexPath *indexPathInTableView;
    id  delegate;
    NSMutableData *activeDownload;
    NSURLConnection *imageConnection;
}
@property (nonatomic, retain) AppRecord *appRecord;
@property (nonatomic, retain) NSIndexPath *indexPathInTableView;
@property (nonatomic, assign) id  delegate;
@property (nonatomic, retain) NSMutableData *activeDownload;
@property (nonatomic, retain) NSURLConnection *imageConnection;
- (void)startDownload;
- (void)cancelDownload;
@end
@protocol IconDownloaderDelegate 
- (void)appImageDidLoad:(NSIndexPath *)indexPath;
@end

.m 文件 -

#import "IconDownloader.h"
#import "MixtapeInfo.h"
#define kAppIconHeight 48
#define TMP NSTemporaryDirectory()
@implementation IconDownloader
@synthesize appRecord;
@synthesize indexPathInTableView;
@synthesize delegate;
@synthesize activeDownload;
@synthesize imageConnection;
#pragma mark
- (void)dealloc
{
    [appRecord release];
    [indexPathInTableView release];
    [activeDownload release];
    [imageConnection cancel];
    [imageConnection release];
    [super dealloc];
}
- (void)startDownload
{
    self.activeDownload = [NSMutableData data];
    // alloc+init and start an NSURLConnection; release on completion/failure
    NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:
                             [NSURLRequest requestWithURL:
                              [NSURL URLWithString:appRecord.mixtape_image]] delegate:self];
    self.imageConnection = conn;
    [conn release];
}
- (void)cancelDownload
{
    [self.imageConnection cancel];
    self.imageConnection = nil;
    self.activeDownload = nil;
}
#pragma mark -
#pragma mark Download support (NSURLConnectionDelegate)
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [self.activeDownload appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    // Clear the activeDownload property to allow later attempts
    self.activeDownload = nil;
    // Release the connection now that it's finished
    self.imageConnection = nil;
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{   
    // Set appIcon and clear temporary data/image
    UIImage *image = [[UIImage alloc] initWithData:self.activeDownload];
    self.appRecord.mixtape_image_obj = image;
    self.activeDownload = nil;
    [image release];
    // Release the connection now that it's finished
    self.imageConnection = nil;
    // call our delegate and tell it that our icon is ready for display
    [delegate appImageDidLoad:self.indexPathInTableView];
}
@end

这是我们如何使用它 -

#import "IconDownloader.h"
@interface RootViewController : UITableViewController 
{
    NSArray *entries;   // the main data model for our UITableView
    NSMutableDictionary *imageDownloadsInProgress;  // the set of IconDownloader objects for each app
}

在 .m 文件中 -

- (void)startIconDownload:(AppRecord *)appRecord forIndexPath:(NSIndexPath *)indexPath
{
    IconDownloader *iconDownloader = [imageDownloadsInProgress objectForKey:indexPath];
    if (iconDownloader == nil) 
    {
        iconDownloader = [[IconDownloader alloc] init];
        iconDownloader.appRecord = appRecord;
        iconDownloader.indexPathInTableView = indexPath;
        iconDownloader.delegate = self;
        [imageDownloadsInProgress setObject:iconDownloader forKey:indexPath];
        [iconDownloader startDownload];
        [iconDownloader release];   
    }
}

这里代理会自动被调用 -

// called by our ImageDownloader when an icon is ready to be displayed
- (void)appImageDidLoad:(NSIndexPath *)indexPath
{
    IconDownloader *iconDownloader = [imageDownloadsInProgress objectForKey:indexPath];
    if (iconDownloader != nil)
    {
        UITableViewCell *cell = [self.tableView cellForRowAtIndexPath:iconDownloader.indexPathInTableView];
        // Display the newly loaded image
        cell.imageView.image = iconDownloader.appRecord.appIcon;
    }
}