关于iphone：如何创建自己的委托（在C中用户定义的委托）


How to create my own delgate (user defined delegate in objective c)

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您好!我刚接触过iPhone，有人能告诉我吗？如何创建一个代表(用户定义)，我对此做了一个研究，但没有找到满意的答案，任何帮助都会非常感谢。谢谢您

首先定义这样的声明委托-

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@protocol IconDownloaderDelegate;

然后创建这样的委托对象-

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

为其声明属性-

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@property (nonatomic, assign) id <IconDownloaderDelegate> delegate;

定义它-

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@protocol IconDownloaderDelegate

- (void)appImageDidLoad:(NSIndexPath *)indexPath;

@end

然后可以调用此委托的方法-

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[delegate appImageDidLoad:self.indexPathInTableView];

这是图像下载类的完整源代码-

h文件

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@class AppRecord;
@class RootViewController;

@protocol IconDownloaderDelegate;

@interface IconDownloader : NSObject
{
    AppRecord *appRecord;
    NSIndexPath *indexPathInTableView;
    id <IconDownloaderDelegate> delegate;

    NSMutableData *activeDownload;
    NSURLConnection *imageConnection;
}

@property (nonatomic, retain) AppRecord *appRecord;
@property (nonatomic, retain) NSIndexPath *indexPathInTableView;
@property (nonatomic, assign) id <IconDownloaderDelegate> 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

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#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

下面是我们如何使用它-

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#import"IconDownloader.h"

@interface RootViewController : UITableViewController <UIScrollViewDelegate, IconDownloaderDelegate>
{
    NSArray *entries;   // the main data model for our UITableView
    NSMutableDictionary *imageDownloadsInProgress;  // the set of IconDownloader objects for each app
}

在.m文件中

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- (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];  
    }
}

这里是自动调用的委托-

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// 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;
    }
}

这是创建自己的委托的基本概念

代理对于在应用程序中手动控制视图控制器数组内的传输非常有用。使用委托可以很好地管理控制流。

下面是自己的代表的一个小例子……

  • 创建协议类…(仅H)

    • 采样elegate.h

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    #import


    @protocol SampleDelegate
    @optional

    #pragma Home Delegate

    -(NSString *)getViewName;

    @end
  • 在要将其委托给其他类的类中导入上面的协议类。在我的示例中，我正在使用AppDelegate使HomeViewController的对象成为委托。

    • 同时在委托引用中添加上面的DelegateName<>

    owndelegateappdelegate.h(W.ndelegateappdelegate.h)

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    #import"SampleDelegate.h"

    @interface ownDelegateAppDelegate : NSObject <UIApplicationDelegate, SampleDelegate> {

    }

    owndelegateappdelegate.m

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    //setDelegate of the HomeViewController's object as
    [homeViewControllerObject setDelegate:self];

    //add this delegate method definition
    -(NSString *)getViewName
    {
        return @"Delegate Called";
    }

    家庭视图控制器.h

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    #import
    #import"SampleDelegate.h"

    @interface HomeViewController : UIViewController {

        id<SampleDelegate>delegate;
    }

    @property(readwrite , assign) id<SampleDelegate>delegate;

    @end

    家庭视图控制器.h

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    - (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];
    }