进击的Objective-C-------------------Block

1.block的四种形式

无参无返回值:

void (^b1)() = ^(){// 定义跟函数指针的形式类似

        NSLog(@"hello!!!");}; b1();

无参有返回值:

int(^b2)() = ^(){ return 1;  };// 花括号外面有分号

 NSLog(@"%d",b2());

有参无返回值:

void (^b3)(int,int) = ^(int a,int b){

        NSLog(@"%d",a+b); }; b3(3,5);

有参有返回值:

int (^b4)(int ,int ) = ^(int a,int b){

        return a > b ? a : b; };  NSLog(@"%d",b4(3,4));

2.block的typedef的两种形式

1⃣️:

typedef int (^BB) (int,int);

BB mb1 = ^(int a,int b){

        return a+b; };

NSLog(@"%d",mb1(3,5));

2⃣️:

typedef int (BBB)(int,int);

BBB ^mb2 = ^(int a,int b){

        return a > b ? a : b;

    }; NSLog(@"%d",mb2(3,5));

3.block和变量

1⃣️:

void (^b1)(int ) = ^(int i){// 形参

        i = 10;// 形参只是拷贝了实参的值,本身的值不会改变

        NSLog(@"%d",i);

    }; b1(5);// 实参  并没有重复定义变量

2⃣️:

    static int i = 10;// 用static修饰之后,变量放在静态区

// __block int i = 10;//   --全局变量(也可以放在主函数外)

    void(^b2)() = ^(){

   i = i+2;   NSLog(@"%d",i);   }; b2();

//如果想要在block中使用局部变量i

// 1局部变量可以被访问

// 2局部变量不可以再次被赋值(仅仅是做了一个拷贝)如果想赋值必须使用__block关键字修饰

4.block和数组排序

1⃣️:

    NSArray *arr1 = [NSArray arrayWithObjects:

@"abcb",@"abca",@"abcd",@"abcc", nil];

    // 这是系统typedef了一个block 给他赋值要用block形式 用来排序

    NSComparator sort = ^(NSString *s1,NSString *s2){

        return [s1 compare:s2]; };

    NSLog(@"%@",[arr1 sortedArrayUsingComparator:sort]);

2⃣️:

NSArray *arr2 = [arr1 sortedArrayUsingComparator:

^NSComparisonResult(NSString * obj1, NSString * obj2) {

//        if ([obj1 compare:obj2] == NSOrderedDescending) {

//            return NSOrderedDescending;

//        }else if ([obj1 compare:obj2] == 0){

//            return NSOrderedSame;

//        }

//        else return NSOrderedAscending; }]; NSLog(@"%@",arr2);

附加:

代码1:

    // 返回值是一个数组,参数也是个数组 实现数组的排序

1⃣️:

    NSMutableArray * (^b6)(NSMutableArray *) = ^(NSMutableArray *arr){
        for (int i = 0; i < [arr count] - 1; i++) {
            for (int j = 0; j < [arr count] - 1 - i; j++) {
                if ([arr[j]compare:arr[j + 1]] == NSOrderedAscending) {
                    [arr exchangeObjectAtIndex:j withObjectAtIndex:j+1];
                }
            }
        }
      return arr;

    };

NSMutableArray *mArr = [NSMutableArray arrayWithObjects:@"aaa",@"bbb",@"ccc", nil];

    NSLog(@"%@",b6(mArr));

2⃣️:

    NSMutableArray *(^sort)(NSMutableArray *) = ^(NSMutableArray *arr){

        [arr sortUsingSelector:@selector(compare:)];

//        [arr sortedArrayUsingSelector:@selector(compare:)];// 不可变数组

 // 系统自带了一个方法 名字叫compare: 默认为升序

        return arr; };

NSMutableArray *marr = [NSMutableArray arrayWithObjects:@"12",@"15",@"13", nil]; NSLog(@"%@",sort(marr));

代码2:

- (NSString *)description{
    return [NSString stringWithFormat:@"name:%@ age:%ld",self.name,self.age];

}

Person *p1 = [[Person alloc]initWithName:@"kobi" age:18];

Person *p2 = [[Person alloc]initWithName:@"james" age:15];

Person *p3 = [[Person alloc]initWithName:@"durant" age:20];

NSArray *Arr = [NSArray arrayWithObjects:p1,p2,p3, nil];

使用block 分别用年龄和姓名对数组进行排序

NSArray *arr3 = [Arr sortedArrayUsingComparator:^NSComparisonResult(Person * obj1, Person * obj2) {
        if ([obj1.name compare:obj2.name] == 1) {
            return NSOrderedDescending;
        }else if ([obj1.name compare:obj2.name] == -1){
            return NSOrderedAscending;
        }
        else
            return NSOrderedSame;
    }];
    NSArray *arr4 = [Arr sortedArrayUsingComparator:^NSComparisonResult(Person* obj1, Person* obj2) {
        if (obj1.age > obj2.age) {
            return NSOrderedDescending;
        }else if (obj1.age < obj2.age){
            return NSOrderedAscending;
        }
        else
            return NSOrderedSame;
    }];
    NSLog(@"%@",arr3);

    NSLog(@"%@",arr4);