const static 在oc中的用法

最新推荐文章于 2025-04-07 15:52:16 发布

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最新推荐文章于 2025-04-07 15:52:16 发布

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原文链接：http://www.cnblogs.com/NSNULL/p/4489641.html

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本文讲解了在Objective-C中如何正确地使用static和const关键字来声明局部常量，特别是kAnimationDuration变量的作用域和不可变性，避免了链接错误并确保了动画持续时间的稳定。

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const表示不能修改 static表示作用域限定在本文件中

// EOCAnimatedView.h
#import <UIKit/UIKit.h>

@interface EOCAnimatedView : UIView
- (void)animate;
@end

// EOCAnimatedView.m
#import "EOCAnimatedView.h"

static const NSTimeInterval kAnimationDuration = 0.3;

@implementation EOCAnimatedView
- (void)animate {
    [UIView animateWithDuration:kAnimationDuration
                     animations:^(){
                         // Perform animations
                     }];
}
@end

It is important that the variable is declared as both static and const. The const qualifier means that the compiler will throw an error if you try to alter the value. In this scenario, that’s exactly what is required. The value shouldn’t be allowed to change. The staticqualifier means that the variable is local to the translation unit in which it is defined. A translation unit is the input the compiler receives to generate one object file. In the case of Objective-C, this usually means that there is one translation unit per class: every implementation (.m) file. So in the preceding example, kAnimationDuration will be declared locally to the object file generated from EOCAnimatedView.m. If the variable were not declared static, the compiler would create an external symbol for it. If another translation unit also declared a variable with the same name, the linker would throw an error with a message similar to this:

Click here to view code image

duplicate symbol _kAnimationDuration in:
EOCAnimatedView.o
EOCOtherView.o

转载于:https://www.cnblogs.com/NSNULL/p/4489641.html