用类封装协议以避免在程序中增加判断语句

在使用FBConnect的FBDialog功能时，需要有一个FBLoginDialog和一个FBStreamDialog。然而FBDialog的Delegate只有一个，因此在FBLoginDialog和FBStreamDialog中各添加了一个布尔值变量以判断需执行哪个Dialog的操作。

但是，该方法只能在两个Dialog的情况下可以使用，如果出现了两个以上的Dialog，则会使程序的结构变得极为复杂。

因此，可以改为创造一个FBDialog类，该类实现 了FBDialogDelegate协议，再在程序中实现该Dialog类的两个对象，这样就可以使不同的FBDialog去调用各自的Callback而不会再产生冲突。而且修改成类的封装后使程序的灵活性大为提高，如果今后再需要增加Dialog的数量，只需再实现一个Dialog类的对象即可，而不用对原有程序做大幅的改动。

FBDialogEventHandler.h:

#import <Foundation/Foundation.h>
#import "FBConnect/FBConnect.h"

@interface FBDialogEventHandler : NSObject <FBDialogDelegate> {
	id mTarget;
	SEL mSucceedHandler;
	SEL mCancelHandler;
	SEL mErrorHandler;
}

@property (nonatomic, assign) SEL succeedHandler;
@property (nonatomic, assign) SEL cancelHandler;
@property (nonatomic, assign) SEL errorHandler;
- (id)initWithTarget:(id)target;

@end

FBDialogEventHandler.m:

#import "FBDialogEventHandler.h"

@implementation FBDialogEventHandler

@synthesize succeedHandler = mSucceedHandler;
@synthesize cancelHandler = mCancelHandler;
@synthesize errorHandler = mErrorHandler;

- (id)initWithTarget:(id)target {
	if (self = [super init]) {
		mTarget = target;
	}
	return self;
}

- (void)dealloc {
	[super dealloc];
}

#pragma mark -
#pragma mark FBDialogDelegate
- (void)dialogDidSucceed:(FBDialog*)dialog {
	[mTarget performSelector:mSucceedHandler withObject:dialog];
}

- (void)dialogDidCancel:(FBDialog*)dialog {
	[mTarget performSelector:mCancelHandler withObject:dialog];
}

- (void)dialog:(FBDialog*)dialog didFailWithError:(NSError*)error {
	[mTarget performSelector:mErrorHandler withObject:error];
}

- (BOOL)dialog:(FBDialog*)dialog shouldOpenURLInExternalBrowser:(NSURL*)url {
	return YES;
}

@end

然后，在头文件中声明:

- (void)loginDialogDidSucceed:(FBDialog *)dialog;
- (void)loginDialogDidCancel:(FBDialog *)dialog;
- (void)loginDialog:(FBDialog *)dialog didFailWithError:(NSError *)error;
- (void)feedDialogDidSucceed:(FBDialog *)dialog;
- (void)feedDialogDidCancel:(FBDialog *)dialog;
- (void)feedDialog:(FBDialog *)dialog didFailWithError:(NSError *)error;

再在程序中加入:

		mFBLoginHandler = [[FBDialogEventHandler alloc] initWithTarget:self];
		mFBLoginHandler.succeedHandler = @selector(loginDialogDidSucceed:);
		mFBLoginHandler.cancelHandler = @selector(loginDialogDidCancel:);
		mFBLoginHandler.errorHandler = @selector(loginDialog:didFailWithError:);
		mFBPostFeedHandler = [[FBDialogEventHandler alloc] initWithTarget:self];
		mFBPostFeedHandler.succeedHandler = @selector(feedDialogDidSucceed:);
		mFBPostFeedHandler.cancelHandler = @selector(feedDialogDidCancel:);
		mFBPostFeedHandler.errorHandler = @selector(feedDialog:didFailWithError:);