iOS开发-block使用与多线程

• Block
• Block封装了一段代码,可以在任何时候执行
• Block可以作为函数参数或者函数的返回值，而其本身又可以带输入参数或返回值。
• 苹果官方建议尽量多用block。在多线程、异步任务、集合遍历、集合排序、动画转场用的很多

#include<stdio.h>
int sum(int a,int b)
{
    return a + b;
}

int main()
{

        NSLog(@"%d",sum(,));

        //如何定义block
        //void (^myblock)       ()       =    ^()       {   };
        //类型（^block的名称）（参数类型）    =  (参数类型)   {代码内容};
        //使用：类似于函数调用

        int (^Sumblock)(int,int) = ^(int a,int b){
            return a + b;
        };

        NSLog(@"%d",Sumblock(,));

        void (^block) () = ^() // 若无参数，后面的（）可以省略
        {
            NSLog(@"------");
        };

        block();

        //跟指针指向函数类似,能用block代替就用
        int (*p)(int,int) = sum;
        int p1 = p(,);
        NSLog(@"%d",p1);

    return ;
}

• 在声明的同时定义变量，然后赋值

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

return a + b;

};

• 也可先用typedef先声明类型，再定义变量进行赋值

typedef int (^MySum)(int,int);

MySum sum = ^(int a,int b) {

return a + b;

};

//
//  ViewController.m
//  SlowWorker
//
//  Created by  Jierism on 16/7/31.
//  Copyright © 2016年  Jierism. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIButton *startButton;
@property (weak, nonatomic) IBOutlet UITextView *resultsTextView;
@property (weak, nonatomic) IBOutlet UIActivityIndicatorView *spinner;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (NSString *) fetchSomethingFromServer
{
    [NSThread sleepForTimeInterval:];
    return @"Hi there";
}

- (NSString *)processData:(NSString *)data
{
    [NSThread sleepForTimeInterval:];
    return [data uppercaseString];
}

- (NSString *)calculateFirstResult:(NSString *)data
{
    [NSThread sleepForTimeInterval:];
    return [NSString stringWithFormat:@"Number of chars:%lu",(unsigned long)[data length]];
}

- (NSString *)calculateSecondResult:(NSString *)data
{
    [NSThread sleepForTimeInterval:];
    return [data stringByReplacingOccurrencesOfString:@"E" withString:@"e"];
}

- (IBAction)doWork:(id)sender
{
    self.resultsTextView.text = @"";
    NSDate *startTime = [NSDate date];
    // 点击后按钮变为禁用状态
    self.startButton.enabled = NO;

    // 让旋转器转动
    [self.spinner startAnimating];
    // 使用dispatch_get_global_queue（1.指定优先级，2.目前没使用为0）函数，来抓取一个已经存在并始终可用的全局队列
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, );
    dispatch_async(queue,  ^{
        NSString *fetchedData = [self fetchSomethingFromServer];
        NSString *processedData = [self processData:fetchedData];
        // 使用分派组（dispatch group），通过dispatch_group_async（）函数异步分派的所有代码块设置为松散，以便尽可能快执行。如果可能，将他们分发给多个线程同时执行(并发).
        __block NSString *firstResult;
        __block NSString *secondResult;
        dispatch_group_t group = dispatch_group_create();
        dispatch_group_async(group, queue, ^{
            firstResult = [self calculateFirstResult:processedData];
        });
        dispatch_group_async(group, queue, ^{
            secondResult = [self calculateSecondResult:processedData];
        });
        // 使用dispatch_group_notify（）指定一个额外的代码块，让它在组中的所有代码块运行完成时再执行。
        dispatch_group_notify(group, queue, ^{
            NSString *resultsSummary = [NSString stringWithFormat:@"First:[%@]\nSecond:[%@]",firstResult,secondResult];
            // 调用分派函数，将工作传回主线程
            dispatch_async(dispatch_get_main_queue(), ^{
                self.resultsTextView.text = resultsSummary;
                self.startButton.enabled = YES;
                [self.spinner stopAnimating];
            });

            NSDate *endTime = [NSDate date];
            NSLog(@"Completed in %f seconds",[endTime timeIntervalSinceDate:startTime]);// 运行时间减少了
        });

    });
}

@end