How to use protocol instead of delegate in iPhone - iphone

Question

Scenario: Need to execute CustomWebview delegate on view controller.
Please help me with this code. Instead of using callback, I need to use "Protocol". Can it be done or we can only use callback in this scenario.
On ViewController.m
- (void)viewDidLoad
{
[super viewDidLoad];
//MyWebView *webView = [[MyWebView alloc] initWithDelegate:self callback:#selector(finishLoading)];
MyWebView *webView= [[MyWebView alloc] initWithFrame:CGRectMake(0,0,320, 460)];
[webView LoadURL:#"http://192.168.5.165/"];
[webView setDelegate:self];
[webView setCallback:#selector(finishLoading)];
[self.view addSubview:webView] ;
}
- (void) finishLoading
{
NSLog(#"Finish");
}
On MyWebView.h
#interface MyWebView : UIView<UIWebViewDelegate> {
NSString *strURL;
}
#property(nonatomic, retain) NSString *strURL;
#property (nonatomic, assign) id delegate;
#property (nonatomic, assign) SEL callback;
-(void) LoadURL:(NSString*)url;
#end
On MyWebView.m
#import "MyWebView.h"
#implementation MyWebView
#synthesize strURL,delegate,callback;
UIWebView *webView;
-(id) initWithFrame:(CGRect)frame
{
if(self =[super initWithFrame:frame])
{
webView = [[UIWebView alloc] initWithFrame:frame];
webView.delegate = self;
[self addSubview:webView];
}
return self;
}
-(void) LoadURL:(NSString*)url
{
NSURL *u = [NSURL URLWithString:url];
NSURLRequest *req= [NSURLRequest requestWithURL:u];
[webView loadRequest:req];
}
- (void)webViewDidFinishLoad:(UIWebView *)webView
{
[delegate performSelector:callback];
}

Answer 1

Your question is a bit unclear. A protocol and a delegate are two entirely separate, though related, things--apples and oranges. A protocol defines a list of methods an object may or must respond to:
#protocol Document
+ (id)documentWithContentsOfURL: (NSURL *)aURL;
- (void)writeToURL: (NSURL *)aURL error: (NSError **)outError;
#end
A delegate is an object, usually an instance of a custom class, that is handed to another object for custom processing or feedback--that latter object delegates work to the delegate object.
Are you asking how to convert a delegate category on NSObject to a delegate protocol? (The former used to be Apple's pattern for defining the obligations and abilities of a delegate; the latter is the newer way to do the same thing.) If so, it generally looks something like this:
Delegate Category on NSObject
#interface NSObject (WidgetDelegate)
- (void)doSomethingWithWidget: (Widget *)w;
#end
#interface Widget : NSObject
#property (readwrite, assign) id delegate;
#end
Delegate Protocol
#protocol WidgetDelegate <NSObject>
- (void)doSomethingWithWidget: (Widget *)w;
#end
#interface Widget : NSObject
#property (readwrite, assign) id <WidgetDelegate> delegate;
#end
Is that what you're looking for? If not, can you clarify exactly what you're trying to do?

Answer 2

Also see Apple's Communicating with Objects, which discusses delegates, protocols, and selectors. Though its listed under Mac OS X, most (if not all) appears to apply to iOS also.

Answer 3

On ViewController.m
#interface MyViewController : UIViewController<MyFinishLoadingDelegate> {
//your own definition
}
- (void)viewDidLoad
{
[super viewDidLoad];
//MyWebView *webView = [[MyWebView alloc] initWithDelegate:self callback:#selector(finishLoading)];
MyWebView *webView= [[MyWebView alloc] initWithFrame:CGRectMake(0,0,320, 460)];
[webView LoadURL:#"http://192.168.5.165/"];
[webView setDelegate:self];
[self.view addSubview:webView] ;
}
- (void)finishLoading //this is your implementation for MyFinishLoadingDelegate
{
NSLog(#"Finish");
}
On MyWebView.h
//you declare the protocol here to tell anyone who'd like to act like your delegate that they need to implement "finishLoading"
#protocol MyFinishLoadingDelegate <NSObject>
- (void)finishLoading;
#end
#interface MyWebView : UIView<UIWebViewDelegate> {
NSString *strURL;
}
#property(nonatomic, retain) NSString *strURL;
#property (nonatomic, assign) id<MyFinishLoadingDelegate> delegate;
-(void) LoadURL:(NSString*)url;
#end
On MyWebView.m
- (void)webViewDidFinishLoad:(UIWebView *)webView
{
[delegate finishLoading];
}