UIViewController viewDidLayoutSubviews

Question

我很難搞清楚爲什麼Erica Sadun在她的食譜例子Ch07-11中做了以下操作（在viewDidLayoutSubviews中調用viewDidAppear）。也許這兩種方法應該調用另一種方法呢？

請參見：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，爲什麼？

Answer 1

這似乎對我來說是完全錯誤的。讓UIKit在這些方法被調用時處理。

而是執行此操作：

 
- (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

因爲viewDidLayoutSubviews佈局srollView將改變滾動視圖，你已經設置好的up.Then，滾動滾動視圖應該得到小口吃。