10、深入理解Blocks与Operation Queues

深入理解Blocks与Operation Queues

1. Blocks的基础概念

1.1 变量捕获

当在块（Block）内部引用块外部的变量时，块会捕获该变量在其创建时刻的状态。例如：

// Slide up a view controller, and then when the slide animation is
// finished, change its background color to yellow.
// The block captures the value of the "myViewController" variable,
// for use after the animation has completed (which will happen some
// time after this method finishes running)
SomeViewController* myViewController = [ code omitted ];
[self presentModalViewController:myViewController animated:YES completion:^{
    myViewController.view.backgroundColor = [UIColor yellowColor];
}];

此代码中，块捕获了 myViewController 变量的值，以便在动画完成后使用。

1.2 延迟执行与代码聚合

块允许将某些