objective-c - OC编译器是如何处理执行某段代码的？

Question

 CGRect frame=  self.bg.frame;
    
    [UIView   beginAnimations:nil context:nil];
    [UIView  setAnimationDuration:2];
    
    long tag=sender.tag;
    switch (tag) {
        case 10:
            frame.origin.y-=30;
            break;
        case 20:
            frame.origin.y+=30;
            break;
        default:
            break;
    }
    
    self.bg.frame=frame;
    [UIView commitAnimations];

中间这部分代码将被执行动画。
我有一个比较奇葩的问题，就是这部分动画代码，编译器是如何获得的呢？

我的心里是这么想的，当然是伪代码表述：就是用String去截取，把这段代码截取出来去执行。。

求教。。

还有顺便一个问题，我一起问了吧。
self.bg.frame=frame;这样位置就变了。。那么OC或者说IOS肯定是不断监听这个属性的变化的。。那么IOS中事件模型是怎样的呢？

Answer 1

There is another way, which is that it must be executed sequentially. . . Only when commitAnimations is reached is the actual submission.

- (IBAction)move:(UIButton *)sender {
  CGRect frame=  self.bg.frame;
    
    [UIView   beginAnimations:nil context:nil];
    NSLog(@"执行到了这里beginAnimations");
    [UIView  setAnimationDuration:2];
    NSLog(@"执行到了这里setAnimationDuration");
    long tag=sender.tag;
    switch (tag) {
        case 10:
            frame.origin.y-=30;
            break;
        case 20:
            frame.origin.y+=30;
            break;
        default:
            break;
    }
    
    self.bg.frame=frame;
       NSLog(@"执行到了这里2");
    [UIView commitAnimations];
       NSLog(@"commitAnimations");
  
}

The result of the operation:
2015-08-28 1520.020 02 Calculator [1403:73936] The execution reaches here beginAnimations
2015-08-28 1520.021 02 Calculator [1403:73936] Execution reaches here setAnimationDuration
2015-08-28 1520.022 02Calculator[1403:73936] Execution reaches here 2
2015-08-28 1520.022 02Calculator[1403:73936] commitAnimations

That is to say, the code must be executed sequentially. . There is no mention of extracting the code and executing it. self.bg.frame=frame; When executing, there must be something similar to obtaining animation status. .

Answer 2

google: render tree, render tree