在loadView中设置UIView的backgroundColor无效

Question

I have a UIDatePicker in an iOS 7 app. It's added to a view controller (subclass) and it shows up hardly readable because the background is black. (A date picker needs a light background.)

- (void)loadView
{
    self.datePicker = [[UIDatePicker alloc] init];
    ...
    [self.view addSubview:self.datePicker];

    // When placed here, without viewDidAppear, background remains black/transparent
    self.view.backgroundColor = [UIColor whiteColor];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];

    // When places here, the background becomes indeed white.
    self.view.backgroundColor = [UIColor whiteColor];
}

I could of course set the background color of the date picker itself in loadView , and that's what I ended up doing.

But still I don't understand why setting the super view's background color in loadView did not work.

Answer 1

您应该使用-viewDidLoad而不是-loadView 。

Answer 2

As stated documentation the loadView is called when ever the viewcontrollers view property is accessed and the view property is nil . If a NIB is associated with the controller his method wil load the view rom the NIB if not it will create a view.

The documentation also states that if you custom implementation should not call super, but this will require you to create your own view.

self.view = [UIView new]

There is no self.view because you did not to call [super loadView]; , calling super will create the view for you. But you should create your own view if you are overriding this method. As stated in the documentation.

Beter is to use viewDidLoad this called when the view is loaded, either from NIB, storyboard or programmatically.

-(void) viewDidLoad{
    self.datePicker = [[UIDatePicker alloc] init];

    [self.view addSubview:self.datePicker];

    self.view.backgroundColor = [UIColor whiteColor];
}

Answer 3

You should probably be setting the background color in -viewWillAppear: . From the docs for
-[UIViewController loadView] :

The view controller calls this method when its view property is requested but is currently nil. This method loads or creates a view and assigns it to the view property.

I haven't tested it today , but I read this to say self.view is nil when -loadView is called, and until you set it explicitly. The main reason to override -loadView is to customize the UIViewController 's view property, presumably to use a specific subclass of UIView , rather than the generic.