1.协议代理

A.h

#import 
  
   
@class ViewControllerA;

@protocol ViewControllerAdelegate
-(void)changeBgColorFromCtrlA:(ViewControllerA *)aView withColor:(UIColor *)color;
@end

@interface ViewControllerA : UIViewController
@property( assign, nonatomic ) id< ViewControllerAdelegate > delegate;


-(IBAction)changeColorAction:(id)sender;
@end
  

#import "ViewControllerA.h"
#import "ViewControllerB.h"
@interface ViewControllerA ()

@end

@implementation ViewControllerA
@synthesize delegate;


//使用协议代理Delegate
-(IBAction)changeColorAction:(id)sender{
    [delegate changeBgColorFromCtrlA:self withColor:[UIColor grayColor]];
    [[self navigationController] popViewControllerAnimated:YES];
}

@end

最终实现在B

B.h

#import 
  
   
#import "ViewControllerA.h"
@interface ViewControllerB : UIViewController
   
     @end
   
  

#import "ViewControllerB.h"

@implementation ViewControllerB

//响应协议代理Delegate
-(void)changeBgColorFromCtrlA:(ViewControllerA *)aView withColor:(UIColor *)color{
    [self.view setBackgroundColor:color];
}
@end

a.m

//通知中心NSNotificationCenter
-(IBAction)changeColorAction2:(id)sender{
    UIColor *color = [UIColor greenColor];
    [[NSNotificationCenter defaultCenter] postNotificationName:@"ChangeColorKey" object:color];
    [[self navigationController] popViewControllerAnimated:YES];
}

#import "ViewControllerB.h"

@implementation ViewControllerB

- (void)viewDidLoad
{
    [super viewDidLoad];
    //注册
    [[NSNotificationCenter defaultCenter] addObserver:self
											 selector:@selector(changeColor:)
												 name:@"ChangeColorKey"
											   object:nil];
  }


//响应通知中心NSNotificationCenter
- (void)changeColor:(NSNotification *)notification{
    if([notification object] != nil)
    {
        UIColor *color = [notification object];
        [self.view setBackgroundColor:color];
    }
}
@end

NSString *string = @"abc";

比较：[a isEqualToString:b]

匹配开头结尾： [a hasPrefix:@"ab"] ; [a hasSuffix:@".txt"];

忽略大小写比较： [a caseInsensitiveCompare:b] == NSOrderedSame;

拼接： NSString *newS = [NSString stringWithFormat:@"%@%@"，a,b ]; //已有的话用[a appendFormat :[NSString stringWithFormaat:@"hhhhhhh"] ];

分割：（字符串分割）

NSString *string = [[NSString alloc] initWithString:@"One,Two,Three,Four"];
NSArray *array = [string componentsSeparatedByString:@","];

（数组组成字符串）

//从数组合并元素到字符串- componentsJoinedByString:
NSArray *array = [[NSArray alloc] initWithObjects:@"One",@"Two",@"Three",@"Four",nil];
NSString *string = [array componentsJoinedByString:@","];

大写： [a uppercaseString];

小写: [a lowercaseString]

截取：

从头开始：[a substringToIndex:3];

到哪里： [a substringFromIndex:3];

一段： [a substringWithRange:NSMakeRange(0,4)];

文件扩展名： [path pathExtension]

/*----------------从文件读取字符串:initWithContentsOfFile方法----------------*/   
 
NSString *path = @"astring.text";
NSString *astring = [[NSString alloc] initWithContentsOfFile:path];
NSLog(@"astring:%@",astring);
[astring release];
 
 
/*----------------写字符串到文件:writeToFile方法----------------*/   
 
 
NSString *astring = [[NSString alloc] initWithString:@"This is a String!"];
NSLog(@"astring:%@",astring);
NSString *path = @"astring.text";    
[astring writeToFile: path atomically: YES];
[astring release];    

4.NSSArray