要求：在一个UIView界面中又一个lable和Button，想点击按钮之后改变lable的值，用协议委托实现

Protocol（ChangeText.h）:

#import <Foundation/Foundation.h>

@protocol ChangeText <NSObject>

-(void)change:(NSString *)val;

@end



Button.h: 

#import <Foundation/Foundation.h>
#import "ChangeText.h"
@interface Button : NSObject

@property(nonatomic,retain) id<ChangeText> delegate;

-(void)changetext:(NSString *)str;

@end



Button.m: 

#import "Button.h"

@implementation Button

-(void)changetext:(NSString *)val
{
    if ([_delegate respondsToSelector:@selector(change:)]) {
        [_delegate change:val];
    }
}

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

@end




创建一个遵循协议的View

ViewA.h:

#import <Foundation/Foundation.h>
#import "ChangeText.h"
#import "Button.h"
@interface ViewA : NSObject<ChangeText>

@property(nonatomic,retain)NSString* textValue;
@property(nonatomic,retain)Button *btn;

//实现协议的change方法
-(void)change;

@end



View.m: 

#import "ViewA.h"

@implementation ViewA

+viewAWithText:(NSString *)val
{
    ViewA *a = [[[ViewA alloc] init] autorelease];
    a.textValue = @"text";
    //初始化Button，并且将当前实现了协议的ViewA赋给button他的委托方法
    Button *btn = [[[Button alloc] init] autorelease];
    btn.delegate = a;
    a.btn = btn;
    return a;
}

-(void)change:(NSString *)val
{
    self.textValue = val;
    NSLog(@"当前的view中文本值是:%@",self.textValue);
}

-(void)dealloc
{
    [_btn release];
    [_textValue release];
    [super dealloc];
}

@end



main: 

#import <Foundation/Foundation.h>
#import "ViewA.h"
#import "Button.h"
int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        ViewA *view = [ViewA viewAWithText:@"text"];
        NSLog(@"当然view中的文本值是:%@",view.textValue);
        [view.btn changetext:@"lable"];
    }
    return 0;
}



结果：

2013-08-05 17:23:22.754 按钮点击[2144:303] 当然view中的文本值是:text

2013-08-05 17:23:22.756 按钮点击[2144:303] 当前的view中文本值是:lable