Begin iOS7 GCD

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////  ViewController.m//  Begin iOS7 GCD////  Created by zyz on 15-4-1.//  Copyright (c) 2015年 Apple. All rights reserved.//#import "ViewController.h"@interface ViewController ()//storyboard三個控制項@property (weak, nonatomic) IBOutlet UIButton *startButton;@property (weak, nonatomic) IBOutlet UILabel *resultTextView;@property (weak, nonatomic) IBOutlet UIActivityIndicatorView *spinner;@end@implementation ViewController- (NSString *)fetchSomethingFromServer{    [NSThread sleepForTimeInterval:1];    return @"Hi, Here";}- (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"];}//點擊事件- (IBAction)buttonClick:(id)sender {    self.startButton.enabled = NO;    [self.spinner setHidden:NO];    [self.spinner startAnimating];    dispatch_queue_t queue1 = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);    dispatch_async(queue1, ^{        NSLog(@"queue1 Thread is %@",[NSThread currentThread]);        NSDate *startTime = [NSDate date];        NSString *fetchedDate = [self fetchSomethingFromServer];        NSString *processDate = [self processData:fetchedDate];        NSString *firstResult = [self calculateFirstResult:processDate];        NSString *secondResult = [self calculateSecondResult:processDate];                dispatch_queue_t queue2 = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);        dispatch_queue_t queue3 = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);                //注意字串只定義，不會為字串分配空間，追加字串會失敗，這裡定義為空白的正確方式        __block NSString *resultsSummary = [NSString stringWithFormat:@""];                //非同步載入，可能還沒有執行完成就執行主線程的非同步載入        dispatch_async(queue2, ^{            resultsSummary = [NSString stringWithFormat:@"First:[%@]\n",firstResult];            NSLog(@"queue2 Thread is %@",[NSThread currentThread]);        });                dispatch_async(queue3, ^{            resultsSummary = [resultsSummary stringByAppendingString:[NSString stringWithFormat:@"Second:[%@]",secondResult]];            NSLog(@"queue3 Thread is %@",[NSThread currentThread]);        });        dispatch_async(dispatch_get_main_queue(), ^{            //這裡字串仍然為空白，因為非同步載入執行的語句還沒有完成就到了這裡            resultsSummary = [resultsSummary stringByAppendingString:@"1111"];            //label的內容是1111，或者是其他的可能結果            self.resultTextView.text = resultsSummary;            self.resultTextView.backgroundColor = [UIColor brownColor];            [self.spinner stopAnimating];            [self.spinner setHidden:YES];        });        NSDate *endTime = [NSDate date];        NSLog(@"Completed in %f seconds",[endTime timeIntervalSinceDate:startTime]);    });}- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.    [self.spinner setHidden:YES];}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end

Begin iOS7 GCD