ios多線程queue的差異，ios多線程queue

ios多線程queue的差異，ios多線程queue

#import "ViewController.h"#import "View2Controller.h"@interface ViewController (){    UIImageView *img;}@end@implementation ViewController- (void)viewDidLoad{    [super viewDidLoad];    self.view.backgroundColor = [UIColor redColor];        img = [[UIImageView alloc] initWithFrame:CGRectMake(0, 20, 200, 200)];    img.backgroundColor = [UIColor greenColor];    [self.view addSubview:img];        UIButton *btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];    btn.frame = CGRectMake(30, 300, 100, 50);    [btn setTitle:@"下載" forState:UIControlStateNormal];    [btn addTarget:self action:@selector(start) forControlEvents:UIControlEventTouchUpInside];    btn.backgroundColor = [UIColor cyanColor];    [self.view addSubview:btn];        UIButton *btn2 = [UIButton buttonWithType:UIButtonTypeRoundedRect];    btn2.frame = CGRectMake(150, 300, 100, 50);    [btn2 setTitle:@"前往" forState:UIControlStateNormal];    [btn2 addTarget:self action:@selector(jumpTo) forControlEvents:UIControlEventTouchUpInside];    btn2.backgroundColor = [UIColor cyanColor];    [self.view addSubview:btn2];        //[self testcopy];    }/*實驗結果:async + globel  圖片下載成功，顯示有延遲  在main中設定圖片才正常async + main  正常sync + globel  圖片下載成功，顯示有延遲， 在main中設定才正常sync + main 圖片無法下載，線程卡死*/-(void)start{    img.image = nil;        NSLog(@"start");    dispatch_async(dispatch_get_main_queue(), ^{        [self downloadImg];    });    NSLog(@"end");}-(void)downloadImg{    NSString *urlStr = @"http://cdn2.raywenderlich.com/wp-content/uploads/2012/09/iOS_6_feast.png";    NSURL *url = [NSURL URLWithString:urlStr];    NSError *error = nil;    NSData *imgData = [[NSData alloc] initWithContentsOfURL:url options:NSDataReadingUncached error:&error];    NSLog(@"img downloaded  %d",imgData.length);//    dispatch_sync(dispatch_get_main_queue(), ^{//       img.image = [UIImage imageWithData:imgData];//    });    img.image = [UIImage imageWithData:imgData];}-(void)testcopy{    NSArray *a = [NSArray array];    NSMutableArray *b = [NSMutableArray array];    NSMutableArray *c = [a mutableCopy];    NSMutableArray *d = [b copy];//    [c addObject:@"1"];//    [d addObject:@"2"];}

async + globel  圖片下載成功，顯示有延遲  在main中設定圖片才正常async + main  正常sync + globel  圖片下載成功，顯示有延遲， 在main中設定才正常sync + main 圖片無法下載，線程卡死

copy與mutablecopy

copy產生的是不可變的對象

mutablecopy產生的是可變對象。