您在哪里初始化View Controller中的属性值？ [英] Where do you initialize property values in a View Controller?

问题描述

我有一个视图控制器，其属性决定了它的行为。这些是由其父项在 prepareForSegue 中设置的。

I have a view controller with properties that determine its behaviour. These are set by its parent in prepareForSegue.

这在我的程序中引发的潜在错误是父母在问题不能保证设置属性，所以我想有一个默认值。在研究方面，我现在明白Objective C中的属性没有默认值。这给我留下了以下选项：

The potential bug this induces in my program is that the parent in question is not guaranteed to set the properties, so I would like to have a default value. On researching, I now understand that properties in Objective C don't have default values. This left me with the following options:

• 在子视图的 viewDidLoad 方法。但是，在调查中， viewDidLoad 在父母的 prepareForSegue 之后被称为 - 所以我会在父实际设置属性时覆盖父级的值。


• 然后我认为我可以使用（id）init 来初始化值，但是，至少在使用故事板时，根本不调用此方法！

• Set the default values for properties in the child view's viewDidLoad method. However, on investigation, viewDidLoad is called after prepareForSegue in the parent - so I would be overwriting the parent's values when the parent actually does set the properties.
• I then thought I could use (id) init to initialize the values, but, at least when using storyboards, this method isn't called at all!

我可能有一个解决方法对象将初始化为默认值，但在这种情况下，我要传入的所有内容都是BOOL。并且由于即使没有正确初始化，bool也会有某个值，我无法测试它是否为非零。

I may have a workaround in that objects will initialize to a default value, but in this case all I want to pass in is a BOOL. And since the bool will have some value even if not initialized correctly, I can't test it to see if it is non-nil.

在父级中 prepareForSegue 之前，是否有机会在子视图控制器中初始化值？

Are there any opportunities for initializing value in the child view controller before prepareForSegue in the parent?

推荐答案

覆盖 init 将无济于事，因为它不是 UIViewController 对象的指定初始化程序。手动实例化视图控制器时 - （id）initWithNibName：（NSString *）nibName bundle：（NSBundle *）nibBundle 从故事板加载时被调用 - （id）initWithCoder：（NSCoder *）解码器将被调用。如果要在初始化视图控制器时设置属性，则必须覆盖两个初始化器。

Overriding init will not help as it is not the designated initialiser for UIViewController objects. When manually instantiating a view controller - (id)initWithNibName:(NSString *)nibName bundle:(NSBundle *)nibBundle is called, when loaded from a storyboard - (id)initWithCoder:(NSCoder *)decoder will be called. If you want to set properties when the view controller is initialised you have to override both initialisers.

在研究中，我现在理解属性在Objective C没有默认值。

On researching, I now understand that properties in Objective C don't have default values.

他们这样做。 nil 表示对象， 0 表示整数值， 0.0 表示如果您需要除此之外的默认值，则应在相应的init方法中设置它们。

They do. nil for objects, 0 for integer values, 0.0 for floating points etc. If you need default values other than that you should set them in the appropriate init method.

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