ios多线程queue的差异

最新推荐文章于 2025-08-18 15:23:56 发布

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本文探讨了在 iOS 应用中使用不同方式下载并显示图片的方法，包括同步与异步下载的区别及其对主线程的影响。同时介绍了如何正确地在主线程更新 UI，确保应用的流畅运行。

#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:@"下载" 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];
    
}

/*实验结果:
async + globel  图片下载成功，显示有延迟  在main中设置图片才正常
async + main  正常
sync + globel  图片下载成功，显示有延迟， 在main中设置才正常
sync + main 图片无法下载，线程卡死
*/
-(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  图片下载成功，显示有延迟  在main中设置图片才正常
async + main  正常
sync + globel  图片下载成功，显示有延迟， 在main中设置才正常
sync + main 图片无法下载，线程卡死

copy与mutablecopy

copy产生的是不可变的对象

mutablecopy产生的是可变对象。