iphone - +(void) 在 objective-c 类静态变量构造函数中初始化

Question

我从 here 中找到了一些示例代码.

static UIImage *backgroundImageDepressed;

/**
 *
 */
@implementation DecimalPointButton

+ (void) initialize {
    backgroundImageDepressed = [[UIImage imageNamed:@"decimalKeyDownBackground.png"] retain];
}

是不是像这样 - +(void) initialize 方法在 Objective C 中初始化类(接口(interface))的静态变量？我以前从未见过这个。

Answer 1

此+initialize 方法在The Objective-C Programming Language 中有描述。 .

The runtime system sends an initialize message to every class object before the class receives any other messages and after its superclass has received the initialize message. This gives the class a chance to set up its runtime environment before it’s used. If no initialization is required, you don’t need to write an initialize method to respond to the message.

例如，当调用[DecimalPointButton alloc]时，运行时将检查是否调用了[DecimalPointButton initialize]。如果没有，它将+initialize 类。这确保 backgroundImageDepressed 图像在构造任何 DecimalPointButton 实例之前准备就绪。