錯誤「的表達是不可轉讓」的timerBar.bounds.size.width分配

Question

我試圖創建一個timerbar，但我得到一個錯誤「表達式是不可轉讓」的timerBar.bounds.size.width = 0

(void)viewDidLoad { 
[super viewDidLoad]; 
// Do any additional setup after loading the view, typically from a nib. 

self.view.backgroundColor = [UIColor blueColor]; 

timerBar = [[UIView alloc]initWithFrame:CGRectMake(0, 0, SCREEN_WIDTH , 5)]; 
timerBar.backgroundColor = [UIColor whiteColor]; 
[self.view addSubview:timerBar]; 

[UIView animateWithDuration:2 delay:0 options:UIViewAnimationOptionCurveLinear animations:^{ 
    timerBar.bounds.size.width = 0; 
} completion:^(BOOL finished) { 

}]; 

} 

我究竟做錯了什麼？爲什麼不能分配這個值？

Answer 1

你不能直接設置邊界寬度爲零！

CGFloat width = 0; 
timerBar.bounds = CGRectMake(0, 0, width , 5)