iOS開發-block使用與多線程

• Block
• Block封裝了一段代碼,可以在任何時候執行
• Block可以作為函數參數或者函數的返回值，而其本身又可以帶輸入參數或返回值。
• 蘋果官方建議盡量多用block。在多線程、異步任務、集合遍歷、集合排序、動畫轉場用的很多

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

int main()
{
        
        NSLog(@"%d",sum(5,6));
        
        //如何定義block
        //void (^myblock)       ()       =    ^()       {   };
        //類型（^block的名稱）（參數類型）    =  (參數類型)   {代碼內容};
        //使用：類似於函數調用

 

        int (^Sumblock)(int,int) = ^(int a,int b){
            return a + b;
        };
        
        NSLog(@"%d",Sumblock(11,22));
        
        void (^block) () = ^() // 若無參數，后面的（）可以省略
        {
            NSLog(@"------");
        };
        
        block();
        
        
        //跟指針指向函數類似,能用block代替就用
        int (*p)(int,int) = sum;
        int p1 = p(11,22);
        NSLog(@"%d",p1);
    
    
    return 0;
}

• 在聲明的同時定義變量，然后賦值

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

return a + b;

};

• 也可先用typedef先聲明類型，再定義變量進行賦值

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:1];
    return @"Hi there";
}

- (NSString *)processData:(NSString *)data
{
    [NSThread sleepForTimeInterval:2];
    return [data uppercaseString];
}

- (NSString *)calculateFirstResult:(NSString *)data
{
    [NSThread sleepForTimeInterval:3];
    return [NSString stringWithFormat:@"Number of chars:%lu",(unsigned long)[data length]];
}

- (NSString *)calculateSecondResult:(NSString *)data
{
    [NSThread sleepForTimeInterval:4];
    return [data stringByReplacingOccurrencesOfString:@"E" withString:@"e"];
}

- (IBAction)doWork:(id)sender
{
    self.resultsTextView.text = @"";
    NSDate *startTime = [NSDate date];
    // 點擊后按鈕變為禁用狀態
    self.startButton.enabled = NO;
    
    // 讓旋轉器轉動
    [self.spinner startAnimating];
    // 使用dispatch_get_global_queue（1.指定優先級，2.目前沒使用為0）函數，來抓取一個已經存在並始終可用的全局隊列
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_async(queue,  ^{
        NSString *fetchedData = [self fetchSomethingFromServer];
        NSString *processedData = [self processData:fetchedData];
        // 使用分派組（dispatch group），通過dispatch_group_async（）函數異步分派的所有代碼塊設置為松散，以便盡可能快執行。如果可能，將他們分發給多個線程同時執行(並發).
        __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（）指定一個額外的代碼塊，讓它在組中的所有代碼塊運行完成時再執行。
        dispatch_group_notify(group, queue, ^{
            NSString *resultsSummary = [NSString stringWithFormat:@"First:[%@]\nSecond:[%@]",firstResult,secondResult];
            // 調用分派函數，將工作傳回主線程
            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]);// 運行時間減少了
        });

    });
}

@end