Begin iOS7 GCD

//
//  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三個控件
@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);
        
        //注意字符串只定義，不會爲字符串分配空間，追加字符串會失敗，這裏定義爲空的正確方式
        __block NSString *resultsSummary = [NSString stringWithFormat:@""];
        
        //異步加載，可能尚未執行完成就執行主線程的異步加載
        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(), ^{
            //這裏字符串仍然爲空，由於異步加載執行的語句尚未完成就到了這裏
            resultsSummary = [resultsSummary stringByAppendingString:@"1111"];
            //label的內容是1111，或者是其餘的可能結果
            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