UIViewController viewDidLayoutSubviews

Question

我很难搞清楚为什么Erica Sadun在她的食谱例子Ch07-11中做了以下操作（在viewDidLayoutSubviews中调用viewDidAppear）。也许这两种方法应该调用另一种方法呢？

请参见：https://github.com/erica/iOS-5-Cookbook/tree/master/C07

- (void) viewDidAppear:(BOOL)animated 
{ 
    scrollView.frame = self.view.bounds; 
    scrollView.center = CGRectGetCenter(self.view.bounds); 

    if (imageView.image) 
    { 
     float scalex = scrollView.frame.size.width/imageView.image.size.width; 
     float scaley = scrollView.frame.size.height/imageView.image.size.height; 
     scrollView.zoomScale = MIN(scalex, scaley); 
     scrollView.minimumZoomScale = MIN(scalex, scaley); 
    } 
} 

- (void) viewDidLayoutSubviews 
{ 
    [self viewDidAppear:NO]; 
} 

任何想法，为什么？

Answer 1

这似乎对我来说是完全错误的。让UIKit在这些方法被调用时处理。

而是执行此操作：

 
- (void)viewDidAppear:(BOOL)animated { 
    [super viewDidAppear:animated]; // Always call super with this!!! 

    [self doSomeCustomLayoutStuff]; // I don't actually think this is necessary. viewWillLayoutSubviews is meant for laying out subviews, and gets called automatically in iOS 5 and beyond. 

} 

- (void)viewWillLayoutSubviews { 
    [super viewWillLayoutSubviews]; 

    [self doSomeCustomLayoutStuff]; 
} 

- (void)doSomeCustomLayoutStuff { 
    scrollView.frame = self.view.bounds; 
    scrollView.center = CGRectGetCenter(self.view.bounds); 

    if (imageView.image) 
    { 
     float scalex = scrollView.frame.size.width/imageView.image.size.width; 
     float scaley = scrollView.frame.size.height/imageView.image.size.height; 
     scrollView.zoomScale = MIN(scalex, scaley); 
     scrollView.minimumZoomScale = MIN(scalex, scaley); 
    } 
} 

Answer 2

因为viewDidLayoutSubviews布局srollView将改变滚动视图，你已经设置好的up.Then，滚动滚动视图应该得到小口吃。