如何创建自己的委托(Objective-C中用户定义的委托) [英] How to create my own delegate (user defined delegate in Objective-C)
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问题描述
在iOS上,如何创建委托(用户定义)?
On iOS, how do I create a delegate (user defined)?
推荐答案
首先定义一个声明这样的委托-
First define a declare a delegate like this -
@protocol IconDownloaderDelegate;
然后创建一个这样的委托对象-
Then create a delegate object like this -
@interface IconDownloader : NSObject
{
NSIndexPath *indexPathInTableView;
id <IconDownloaderDelegate> delegate;
NSMutableData *activeDownload;
NSURLConnection *imageConnection;
}
为其声明属性-
@property (nonatomic, assign) id <IconDownloaderDelegate> delegate;
定义它-
@protocol IconDownloaderDelegate
- (void)appImageDidLoad:(NSIndexPath *)indexPath;
@end
然后您可以在此委托上调用方法-
Then you can call methods on this delegate -
[delegate appImageDidLoad:self.indexPathInTableView];
这是图像下载器类的完整源代码-
Here is the complete source code of the image downloader class -
.h文件-
@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-
#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
这是我们的用法-
#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-
- (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];
}
}
这是自动被调用的代表-
here is delegate gets called automatically -
// 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;
}
}
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