块(block)

块(block)

block, 块语法,C语言函数的扩展, 允许在函数内部定义一个block, block执行效率比较高

block的语法(与函数指针的语法非常相似)

返回值类型 (^block名)(参数类型1参数名, 参数类型2参数名2, ...) = ^(参数类型1参数名, 参数类型2参数名2, ...){

功能代码

};

注: 没有参数, 括号不能省略

block变量

数据类型变量名 = 初值

 void (^blockName)() = ^() {
            NSLog(@"Hello, 你好");
            
        };     
        blockName();

写block的思路

1.写成函数怎么写

2.对照写出block()(输入inlineBlock, 会自动提示)

写一个block, "求一个数平方"

int (^doubleNumber)(int number) = ^(int number){
            return number * number;
        };
        
        NSLog(@"%d", doubleNumber(3));

写一个block,求两个数的最大值

int(^blockMax)(int, int) = ^(int a, int b) {
            return a > b ? a : b;
        };
        
        NSLog(@"max = %d", blockMax(3, 4));

写一个返回值为整型参数为NSString（仅一个参数）的block，实现将字符串转换为整型的功能。

NSInteger(^changeToInt)(NSString *string) = ^(NSString *string) {
            return [string integerValue];
        };
        
        NSLog(@"%ld", changeToInt(@"12a3"));

写一个block, 求一个字母对应的ACSII值

//1
        int(^changeASCII1)(char) = ^(char c) {
            int a = c;
            return a;
        };
        NSLog(@"%d", changeASCII1('a'));
    
        //2
        void(^changeASCII)(char) = ^(char a) {
            NSLog(@"%d", a);
        };
        changeASCII('a');

写一个block, 求三个数的中间值

int(^middleValue)(int, int, int) = ^(int a, int b, int c) {
            //1
            //return a > b ? (b > c ? b : (a > c ? c : a)) : (a > c ? a : (b > c ? c : b)) ;
            //2
            return a + b + c - MAX(MAX(a, b), c) - MIN(MIN(a, b), c);
        };
        NSLog(@"middle = %d", middleValue(3, 4, 5));

block的使用

1.使用typedef对block类型重命名

        typedef int (^BlockType)(int, int);   
        BlockType sum = ^(int a, int b){ return a + b; };
        NSLog(@"%d", sum(2, 3));

2.block内部访问变量

block内部不能够修改局部变量的值

如果在block内部修改变量的值, 可以

1.全局变量或静态变量

2.用__block修饰局部变量

写一个block, 打印输出一个整数

//        static int num = 1024;
        __block int  num = 1024;
        void(^printNumber)() = ^() {
            NSLog(@"%d", num);
            num++;
        };
        printNumber();
        printNumber();
        printNumber();

数组排序

NSArray *array = [NSArray arrayWithObjects:@"30", @"12", @"4", @"100" , @"1000", nil];

1.提供相邻元素的比较方法

缺点: 只能升序排序

适用范围: 对姓名按照a->z排序

        NSArray *sortArray = [array sortedArrayUsingSelector:@selector(compare:)];
        NSLog(@"%@", sortArray);

2.提供相邻元素的比较规则

       //写法1
        //比较规则 block
        NSComparisonResult(^rule)(NSString *, NSString *) = ^(NSString *str1, NSString *str2) {
            //满足NSOrderedAscending的条件, 决定了排序的结果
            if ([str1 intValue] > [str2 intValue]) {
                return NSOrderedDescending;
            } else if ([str1 intValue] == [str2 intValue]) {
                return NSOrderedSame;
            } else {
                return NSOrderedAscending;
            }
        };
        
       NSArray *sortArray1 = [array sortedArrayUsingComparator:rule];
       NSLog(@"%@", sortArray1);
        
        //写法2
        NSArray *sortArray2 = [array sortedArrayUsingComparator:^NSComparisonResult(NSString *obj1, NSString *obj2) {
            if ([obj1 intValue] < [obj2 intValue]) {
                return NSOrderedDescending;
            } else if ([obj1 intValue] == [obj2 intValue]) {
                return NSOrderedSame;
            } else {
                return NSOrderedAscending;
            }

        }];
        NSLog(@"%@", sortArray2);

        Student *stu1 = [[Student alloc]initWithName:@"chenqiang" number:2 score:59.9];
        Student *stu2 = [[Student alloc]initWithName:@"bengbeng" number:28 score:40];
        Student *stu3 = [[Student alloc]initWithName:@"gexing" number:41 score:60];
        Student *stu4 = [[Student alloc]initWithName:@"yanglong" number:3 score:70];
        Student *stu5 = [[Student alloc]initWithName:@"yalong" number:61 score:61];
        
        NSArray *studentArray = [NSArray arrayWithObjects:stu1, stu2, stu3, stu4, stu5, nil];

        //分数由高到低
       NSArray *sortByscore = [studentArray sortedArrayUsingComparator:^NSComparisonResult(Student *stu1 , Student *stu2) {
           if ([stu1 score] < [stu2 score]) {
               return NSOrderedDescending;
           } else if ([stu1 score] == [stu2 score]) {
               return NSOrderedSame;
           } else {
               return NSOrderedAscending;
           }
       }];
       
        NSLog(@"%@", stu1);//类名+地址
        
        for (Student *stu in sortByscore) {
            [stu showStudents];
        }
        
    NSLog(@"
***********************华丽的分割线*********************************
");
        //姓名由a-z排序
        NSArray *sortByname = [studentArray sortedArrayUsingComparator:^NSComparisonResult(Student *stu1 , Student *stu2) {
//            if ([[stu1 name] compare: [stu2 name]] == 1) {
//                return NSOrderedDescending;
//            } else if ([[stu1 name] compare: [stu2 name]] == 0) {
//                return NSOrderedSame;
//            } else {
//                return NSOrderedAscending;
//            }
//            NSComparisonResult result = [[stu1 name] compare:[stu2 name]];
            return [[stu1 name] compare:[stu2 name]];
        }];
        
        for (Student *stu in sortByname) {
            [stu showStudents];
        }

语法糖(syntactic sugar)

1.数值(比如100 3.14 YES)前加@, 转化成NSNumber

        NSNumber *number1 = [NSNumber numberWithInt:100];
        NSNumber *number2 = @100;
        NSNumber *number3 = @3.14;
        NSNumber *number4 = @YES;
        
        NSArray *numberArray = [NSArray arrayWithObjects:@100, @3.14, @YES, nil];

2.@""快速创建一个字符串

        NSString *string1 = [[NSString alloc] initWithString:@"abc"];
        NSString *string2 = @"abc";

3.@[]快速创建一个NSArray对象

        NSArray *array1 = [NSArray arrayWithObjects:@"a", @"b", @"c", nil];
        NSArray *array2 = @[@"a", @"b", @"c"];

4.数组名[下标], 访问数组中的某个元素

        NSLog(@"%@", [array1 objectAtIndex:1]);
        NSLog(@"%@", array2[1]);

5.@{}快速创建一个NSDictionary的对象

NSDictionary *dic1 = [[NSDictionary alloc]initWithObjectsAndKeys:@"xiaoming", @"name", @"男", @"gender", @"18", @"age", nil];
        NSDictionary *dic2 = @{@"name":@"xiaoming", @"gender":@"男", @"age":@"18"};

6.字典名[key], 取key对应的value值

        NSLog(@"%@", [dic1 objectForKey:@"name"]);
        NSLog(@"%@", dic2[@"name"]);

The one who wants to wear a crown must bear the weight!