Block

3Block
3.1是一种新的数据（类型）
3.2Block数据类型的Block(变量)存储的是一段儿代码

    int a ;
    void(^myBlock)(void)=^void(void)//定义了一个Block的变量
    {
        [self print:@"Block被执行了"];
    };
    myBlock();
    double(^myBlock1)(double a,double b);
    myBlock1 = ^double(double a,double b)
    {
        return a + b;
    };
    [self print:[NSNumber numberWithDouble: myBlock1(3,5)]];

3.3语法
3.3.1没有固定的关键字
3.3.2其数据类型是由该变量存储代码的返回值类型+形参构成
3.3.3可以使用typedef指定Block数据类型名如：

#import "ViewController+TRPrint.h"
typedef void(^BlockType)(void);
typedef double(^BlockType1)(double a, double b);
@interface ViewController ()

BlockType b1 = ^void(void)//也可写成BlockType b1 = ^，因为返回值类型是void
    {
        [self print:@"用Block类型定义变量"];
    };
    b1();
    BlockType1 b2 = ^double(double a, double b)
    {
        return a - b;
    };
    [self print:[NSNumber numberWithDouble:b2(3,5)]];

3.4Block与全局变量
在扩展里写个定义个全局变量

int g_i = 10;//一个全局变量

然后在viewDidLoad里测试

//Block与全局变量
    BlockType b3 = ^
    {
        [self print:[NSNumber numberWithInt:g_i]];//全局变量在Block中可以被访问
        g_i = 20;//全局变量在Block中可以被赋值
    };
    b3();
    [self print:[NSNumber numberWithInt:g_i]];

3.5Block与局部变量

//Block与局部变量
    int i2 =30;
    __block int i3 = 50;
    BlockType b4 = ^
    {
        [self print:[NSNumber numberWithInt:i2]];//局部变量在Block中可以被访问
        //i2 = 40;//局部变量在Block中不可以被赋值
        i3 = 60;//加上关键字__block后，局部变量才可以在Block中赋值
    };
    b4();
    [self print:[NSNumber numberWithInt:i3]];

3.6Block在自定义类中的使用
TRMyclass.h

typedef void(^MyBlock)(void);
typedef double (^MyBlock1)(double a,double b);
typedef NSString*(^MyBlock2)(void);
@interface TRMyclass : NSObject
-(void)mehtod:(MyBlock)b;
-(NSString*)method1:(MyBlock1)b;
-(MyBlock2)getBlock;
@property MyBlock b;
@end

TRMyclass.m

@implementation TRMyclass
-(void)mehtod:(MyBlock)b
{
    b();//callback回调
}
-(NSString *)method1:(MyBlock1)b
{
    return [NSString stringWithFormat:@"%g",b(2,3)];
}
-(MyBlock2)getBlock
{
    return ^NSString*(void){return @"返回一个block";};
}

在ViewController.m

 //Block在自定义类中的使用
    TRMyclass *m = [[TRMyclass alloc]init];
    [m mehtod:^{
        [self print:@"Block做方法形参"];
    }];
    [m mehtod:^{
        [self print:@"这是多态的表现"];
    }];
    [self print:[m method1:^double(double a, double b) {
        return a + b;
    }]];
    [self print:[m method1:^double(double a, double b) {
        return a - b;
    }]];
    [self print:[m getBlock]()];//Block本质上函数指针
    m.b = ^
    {
        [self print:@"Block做属性"];
    };
    m.b();
}

3.7Block与数组、字典

//Block与数组、字典
    TRStudent *stu1 = [TRStudent studentWithName:@"张三" andAge:18];
    TRStudent *stu2 = [TRStudent studentWithName:@"李四" andAge:20];
    TRStudent *stu3 = [TRStudent studentWithName:@"王五" andAge:19];
    NSComparisonResult(^sort)(id  _Nonnull obj1, id  _Nonnull obj2)= ^NSComparisonResult(id  obj1, id obj2) {
        NSNumber *selfAge = [NSNumber numberWithInt:[obj1 age]];
        NSNumber *otherAge = [NSNumber numberWithInt:[obj2 age]];
        return [selfAge compare:otherAge];
    };
    //Block与数组
    NSArray *stuArray = @[stu1,stu2,stu3];
    NSArray *sortedArray = [stuArray sortedArrayUsingComparator:sort];
    NSMutableString *str = [NSMutableString stringWithCapacity:15 *3];
    for(TRStudent *s in sortedArray)
    {
        [str appendFormat:@"%@\n",s];
    }
    self.outputLabel.text = str;
    //Block与字典
    NSDictionary *stuDict = @{@"1":stu1,@"2":stu2,@"3":stu3};
NSArray *sortedDict = [stuDict keysSortedByValueUsingComparator:sort];
    str = [NSMutableString stringWithCapacity:15 *3];
    for (NSString *key in sortedDict)
    {
        [str appendFormat:@"%@",stuDict[key]];
    }
    [self print:str];
}