在超类上调用-initWithFrame:

问题描述

有人可以帮我理解为什么我们在初始化之前先在 super 上调用初始化方法的原因.我在UIView的子类中遇到了一段代码，想知道在这里总是调用myMethod，这意味着我没有在 UIView 中设置框架，那么为什么我们要这样做并使用 if 条件.

Can someone help me understanding as why do we call an initialization method on super first before initializing. I came across a piece of code in a subclass of UIView and wanted to know that here myMethod is always getting called that means I am not getting the frame set in UIView, then why are we doing this and using an if condition.

self = [super initWithFrame:CGRectMake(0, 0, 20, 100)];
if(self != nil) {
  [self myMethod:data];
  self.backgroundColor = [UIColor clearColor];
}
return self;

推荐答案

假设我有一个名为 SpinningView 的 UIView 子类.创建 spinningView 的代码如下所示:

Let's say I have a UIView subclass called SpinningView. The code to create spinningView would look like this:

SpinningView * spinner = [[Spin​​ningView alloc] initWithFrame:CGRectMake(0.0，0.0，20.0，20.0)]

现在让我们看一下SpinningView的 -initWithFrame:方法的实现

Now let's take a look at the implementation of SpinningView's -initWithFrame: method

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];

    if (self)
    {
        self.backgroundColor = [UIColor clearColor];
    }

    return self;
}

第一行是简单的分配.我们将自己分配给 -UIView 的 -initWithFrame:

The first line is simple assignment. We're assigning ourselves to the result of UIView's implementation of -initWithFrame:

我们使用if语句查看self甚至是否有效.如果不是，我们将其退回.如果是这样，我们对其进行配置.

We use the if statement to see if self is even valid. If it's not we just return it. If it is, we configure it.

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