覆盖子类中的init [英] Overriding init in subclass

问题描述

在Objective-C中，是否有必要覆盖子类的所有继承构造函数以添加自定义初始化逻辑？

In Objective-C, is it necessary to override all inherited constructors of a subclass to add custom initialization logic?

例如，以下内容对于a是否正确 UIView 具有自定义初始化逻辑的子类？

For example, would the following be correct for a UIView subclass with custom initialization logic?

@implementation CustomUIView

- (id)init {
    self = [super init];
    if (self) {
        [self initHelper];
    }
    return self;
}

- (id)initWithFrame:(CGRect)theFrame {
    self = [super initWithFrame:theFrame];
    if (self) {
        [self initHelper];
    }
    return self;
}

- (id)initWithCoder:(NSCoder *)decoder {
    self = [super initWithCoder:decoder];
    if (self) {
        [self initHelper];
    }
    return self;
}

- (void) initHelper {
    // Custom initialization
}

@end

推荐答案

每个Cocoa Touch（和Cocoa）类都有一个指定的初始值设定项;对于 UIView ，如上所述在本文档中，该方法是 initWithFrame：。在这种特殊情况下，您只需要覆盖 initWithFrame ;所有其他调用将最终级联并最终命中此方法。

Every Cocoa Touch (and Cocoa) class has a designated initializer; for UIView, as stated in this documentation, that method is initWithFrame:. In this particular case, you'll only need to override initWithFrame; all other calls will cascade down and hit this method, eventually.

这超出了问题的范围，但是如果你最终创建一个带有额外参数的自定义初始值设定项，在分配 self 时，你应该确保超类的指定初始值设定项，如下所示：

This goes beyond the scope of the question, but if you do end up creating a custom initializer with extra parameters, you should make sure to the designated initializer for the superclass when assigning self, like this:

- (id)initWithFrame:(CGRect)theFrame puzzle:(Puzzle *)thePuzzle title:(NSString *)theTitle {
    self = [super initWithFrame:theFrame];
    if (self) {
        [self setPuzzle:thePuzzle];
        [self setTitle:theTitle];
        [self initHelper];
    }
    return self;
}

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