精通IOS開發-block使用與多線程

標籤：

• 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傳回值，而其本身又可以帶輸入參數或傳回值。
• 蘋果官方建議盡量多用block。在多線程、非同步任務、集合遍曆、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，後面的（）可以省略        {            NSLog(@"------");        };                block();                        //跟指標指向函數類似,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數，然後賦值

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

return a + b;

};

• 也可先用typedef先宣告類型，再定義變數進行賦值

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];    // 點擊後按鈕變為禁用狀態    self.startButton.enabled = NO;        // 讓旋轉器轉動    [self.spinner startAnimating];    // 使用dispatch_get_global_queue（1.指定優先順序，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域隊列    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];        // 使用指派組（dispatch group），通過dispatch_group_async（）函數非同步指派的所有代碼塊設定為鬆散，以便儘可能快執行。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];            // 調用指派函數，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]);// 已耗用時間減少了        });    });}@end

 

精通IOS開發-block使用與多線程