在 Objective-C 类别中初始化一个静态变量

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2022-01-01 3

Initialising a static variable in Objective-C category(在 Objective-C 类别中初始化一个静态变量)

本文介绍了在 Objective-C 类别中初始化一个静态变量的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我试图创建一个静态变量来存储图像字典.不幸的是，我能找到的最好的初始化方法是检查每个使用该变量的函数.由于我在一个类别中创建这个变量，我不能只在初始化程序中初始化它.有没有更简洁的方法来初始化 navigationBarImages?

I was trying to create a static variable to store a dictionary of images. Unfortunately, the best way I could find to initialise it was to check in each function that used the variable. Since I am creating this variable inside a category, I can't just initialise it inside the initialiser. Is there a neater way of initialising navigationBarImages?

static NSMutableDictionary *navigationBarImages = NULL;

@implementation UINavigationBar(CustomImage)
//Overrider to draw a custom image
- (void)drawRect:(CGRect)rect
{
    if(navigationBarImages==NULL){
        navigationBarImages=[[NSMutableDictionary alloc] init];
    }
    NSString *imageName=[navigationBarImages objectForKey:self];
    if (imageName==nil) {
        imageName=@"header_bg.png";
    }
    UIImage *image = [UIImage imageNamed: imageName];
    [image drawInRect:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];
}

//Allow the setting of an image for the navigation bar
- (void)setImage:(UIImage*)image
{
    if(navigationBarImages==NULL){
        navigationBarImages=[[NSMutableDictionary alloc] init];
    }
    [navigationBarImages setObject:image forKey:self];
}
@end

推荐答案

__attribute__((constructor))
static void initialize_navigationBarImages() {
  navigationBarImages = [[NSMutableDictionary alloc] init];
}

__attribute__((destructor))
static void destroy_navigationBarImages() {
  [navigationBarImages release];
}

这些函数会在程序启动和结束时自动调用.

These function will be called automatically when the program starts and ends.

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