OC语言 - block：定义 | 用作参数

block | 函数

1 - 相同点

① 都可以保存代码

② 参数、返回值均可有可无

③ 调用方式一样　           

block 本质上是匿名函数，同样也是 OC对象。在 iOS 4.0 之后的类都添加了 block 支持

如何使用 block

1 - 定义一个 block 

    // 标准格式
    int (^maxBlock)(int a, int b) = ^int (int x,int y){

        return  x > y ? x : y;
    };

    int maxNumber = maxBlock(32,55);
    NSLog(@"%d",maxNumber);


    // 右边返回值类型可省略；左边可省略参数
    int (^block02)(int) = ^(int x){

        return x*x;
    };
    int result02 = block02(9);
    NSLog(@"%d",result02);


    // 无参无返回值
    void(^block03)(void) = ^void(){
        NSLog(@"The block03!");
    };
    block03();
    // 无参时：左边参数括号是不能省略的；右边返回类型、参数括号均可省略
    void(^block04)(void) = ^{
        NSLog(@"Fuck the block04!");
    };
    block04();

2 - block 同函数指针十分相似

// 定义一个函数
int maxValue (int a , int b){
  　return a > b ? a : b;
}

// 函数指针  
int maxNumber = maxValue(18,59);
// 函数指针
int (*p)(int,int) = maxValue;
int result = p(10,15);

3 - 开发中往往使用 typedef 关键字用来简化代码

#import <Foundation/Foundation.h>

// typedef 可以大大简化 block 声明，写出通俗易懂的代码
typedef int (^myBlock)(int,int);
int main(int argc, const char * argv[]) {
    @autoreleasepool {

        // 方式一
        myBlock block01;
        block01 = ^(int a,int b){
            
            return a+b;
        };
        NSLog(@"%d",block01(123,3));// 调用
        
        
        // 方式二
        myBlock block02 = ^(int num1,int num2){
            
            return num1*num2;
        };
        NSLog(@"%d",block02(123,3));// 调用
    }
    return 0;
}

4 - 下面我们手写几个 block，熟悉其使用方式

① 处理字符串

    // 分割字符串
    NSString *(^blockSeg)(NSString *str01,NSString *str02) = ^NSString*(NSString *st01,NSString *st02){

        return [[st01 componentsSeparatedByString:st02] firstObject];
    };
    NSString *strSub = blockSeg(@"I love my honey W , forever !",@",");
    NSLog(@"%@",strSub);// I love my honey W

    // 拼接字符串
    NSArray *array01 = [NSArray arrayWithObjects:@"美女",@"喜欢",@"野兽", nil];
    // 方式一
    NSString *(^appendingStringBlock01)(NSArray *) = ^(NSArray * array){
        NSMutableString *str = [NSMutableString stringWithCapacity:1];
        for (NSString *string in array) {
            [str appendString:string];
        }
        return [NSString stringWithString:str];
    };
    NSLog(@"%@",appendingStringBlock01(array01));

    // 方式二
    NSString *(^appendingStringBlock02)(NSArray *) = ^(NSArray * array){
        NSString *str = @"";
        for (NSString *string in array) {
            str = [str stringByAppendingString:string];
        }
        return str;
    };
    NSLog(@"%@",appendingStringBlock02(array01));

    // 方式三
    NSString *(^appendingStringBlock03)(NSArray *) = ^(NSArray *array){
        NSString *str = @"";
        for (NSString *string in array) {
            str = [NSString stringWithFormat:@"%@%@",str,string];
        }
        return str;
    };
    NSLog(@"%@",appendingStringBlock03(array01));

② block 排序

// - Person.h

#import <Foundation/Foundation.h>
@interface Person : NSObject

@property(nonatomic,copy)NSString *name;
@property(nonatomic,copy)NSString *sex;
@property(nonatomic,assign)NSInteger  age;
- (id)initWithName:(NSString *)name
               sex:(NSString *)sex
               age:(NSInteger )age;

@end

// - Person.m

#import "Person.h"
@implementation Person

- (id)initWithName:(NSString *)name
               sex:(NSString *)sex
               age:(NSInteger )age{
    self = [super init];
    if (self) {
        _name = name;
        _sex = sex;
        _age = age;
    }
    return self;
}

- (NSString *)description{
    return [NSString stringWithFormat:@"%@,%@,%ld",_name,_sex,_age];
}

@end

// - main.m

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

int main(int argc, const char * argv[]) {

    Person *person1 = [[Person alloc] initWithName:@"刘大" sex:@"男" age:11];
    Person *person2 = [[Person alloc] initWithName:@"陈二" sex:@"女" age:13];
    Person *person3 = [[Person alloc] initWithName:@"张三" sex:@"男" age:15];
    Person *person4 = [[Person alloc] initWithName:@"李四" sex:@"男" age:32];
    Person *person5 = [[Person alloc] initWithName:@"王五" sex:@"女" age:28];

    NSArray *array = [NSArray arrayWithObjects:person1,person2,person3,person4,person5, nil];
    // 年龄升序
    NSArray *newArray = [array sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        Person *per1 = (Person*)obj1;
        Person *per2 = (Person*)obj2;


        if (per1.age > per2.age) {
            return NSOrderedDescending;
        }
        if (per1.age < per2.age) {
            return NSOrderedAscending;
        }else{

            return NSOrderedSame;
        }
    }];
    NSLog(@"%@",newArray);

    
    // 名字排序
    NSArray *array05 = [NSArray arrayWithObjects:@"Jeson",@"Hazell",@"Solina",@"Cacy",@"Lee", nil];
    NSArray *newArray05 = [array05 sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        return [obj1 compare:obj2];   // 升序
        // return [obj2 compare:obj1];// 降序
    }];
    NSLog(@"%@",newArray05);

    return YES;
}

③ 使用 block 模拟迅雷下载（注意值的传向问题）

// - XunLeiDownload.h：

#import <Foundation/Foundation.h>
typedef void (^tetsBlock)(int n);

@interface XunLeiDownload : NSObject

-(void)beginDownload:(tetsBlock)block;

@end

// - XunLeiDownload.m

#import "XunLeiDownload.h"

@implementation XunLeiDownload
// 谁要传值，谁就把 block 用作参数
-(void)beginDownload:(tetsBlock)block{
    
    for (int i = 0; i < 10; i ++) {
        int kb = arc4random() % 100;
        block(kb);// block 作为参数时是从内部向外传值：在外部，谁调用就传给谁
    }
}

@end

// - main.m

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

int main(int argc, const char * argv[]) {
    
    XunLeiDownload *xml = [[XunLeiDownload alloc] init];
    // 外部调用 block
    [xml beginDownload:^(int n) {
        NSLog(@"下载了%d个资源",n); // n 就是从 block 内部传出的 kb
    }];
    
    return YES;
}

④ 使用 block 模拟登录页面：block 用作参数传值且有返回值时（注意返回值的传向）

// - LoginManager.h

#import <Foundation/Foundation.h>
typedef void (^SuccessfulBlock)(NSString*infoBack);
typedef BOOL (^FailBlock) (NSString *errorManager);

@interface LoginManager : NSObject

- (void)loginWithUserName:(NSString *)name
                 password:(NSString *)password
          successfulBlock:(SuccessfulBlock)successBlock
                failBlock:(FailBlock)failBlock;

@end

// - LoginManager.m

#import "LoginManager.h"
@implementation LoginManager

-(void)loginWithUserName:(NSString *)name password:(NSString *)password successfulBlock:(SuccessfulBlock)successBlock failBlock:(FailBlock)failBlock{
    
    
    if ([name isEqualToString:@"123"] && [password isEqualToString:@"12345"]) {
        successBlock([NSString stringWithFormat:@"Hazell，请来小黑屋面谈"]);// 由内向外传值
    }else{
        
        
        NSString *warning = [NSString stringWithFormat:@"警告！%@是非法人员",name];
        int result  =  failBlock(warning);
        
        // block 的返回值是从外向内返回的，block 内部拿到值后继续往下编程
        if (result) {
            NSLog(@"密码是：%@",password);
        }else{
            NSLog(@"%@",[NSString stringWithFormat:@"%@代号已被销毁",name]);
        }
    }
}

@end

// - main.m

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

int main(int argc, const char * argv[]) {
    
    LoginManager *manager = [[LoginManager alloc] init];
    // name=123     password=12345
    [manager loginWithUserName:@"123" password:@"1234" successfulBlock:^(NSString *infoBack) {
        
        NSLog(@"%@",infoBack);// infoBack 从 block 内部传出至此，在该代码块中使用
    } failBlock:^BOOL(NSString *errorManager) {
        
        NSLog(@"%@",errorManager);// errorManager 同 infoBack
        return arc4random()%2 ;   // 返回结果再次传回 block 内部
    }];
    
    return YES;
}