iphone - 如何在不阻塞 iPhone 应用程序中的用户界面的情况下运行进程

Question

我在 iphone 上访问照片库，导入我在我的应用程序中选择的图片需要很长时间，我如何在辅助线程上运行该进程，或者我使用什么解决方案来不阻止用户界面？

Answer 1

我在此处使用 performSelectOnBackground 或 GCD 对示例代码进行了完整解释:

GCD, Threads, Program Flow and UI Updating

这是该帖子的示例代码部分(减去他的具体问题:

performSelectorInBackground 示例:

在这个片段中，我有一个调用长时间运行的工作的按钮，一个状态标签，我添加了一个 slider 来显示我可以在 bg 工作完成时移动 slider 。

// on click of button
- (IBAction)doWork:(id)sender
{
    [[self feedbackLabel] setText:@"Working ..."];
    [[self doWorkButton] setEnabled:NO];

    [self performSelectorInBackground:@selector(performLongRunningWork:) withObject:nil];
}

- (void)performLongRunningWork:(id)obj
{
    // simulate 5 seconds of work
    // I added a slider to the form - I can slide it back and forth during the 5 sec.
    sleep(5);
    [self performSelectorOnMainThread:@selector(workDone:) withObject:nil waitUntilDone:YES];
}

- (void)workDone:(id)obj
{
    [[self feedbackLabel] setText:@"Done ..."];
    [[self doWorkButton] setEnabled:YES];
}

GCD 样本:

// on click of button
- (IBAction)doWork:(id)sender
{
    [[self feedbackLabel] setText:@"Working ..."];
    [[self doWorkButton] setEnabled:NO];

    // async queue for bg work
    // main queue for updating ui on main thread
    dispatch_queue_t queue = dispatch_queue_create("com.sample", 0);
    dispatch_queue_t main = dispatch_get_main_queue();

    //  do the long running work in bg async queue
    // within that, call to update UI on main thread.
    dispatch_async(queue, 
                   ^{ 
                       [self performLongRunningWork]; 
                       dispatch_async(main, ^{ [self workDone]; });
                   });    
}

- (void)performLongRunningWork
{
    // simulate 5 seconds of work
    // I added a slider to the form - I can slide it back and forth during the 5 sec.
    sleep(5);
}

- (void)workDone
{
    [[self feedbackLabel] setText:@"Done ..."];
    [[self doWorkButton] setEnabled:YES];
}