Swift 使用runtime给extension添加属性

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前言

最近使用swift写新项目，也算是试水，虽然现在swift算是推广起来了，很多大厂小公司的新项目都是swift，但是还是不少坑，这两天写一个waveView就遇到了个这个问题

一般再OC中使用runtime给分类添加属性是这个样子的objc_setAssociatedObject 和objc_getAssociatedObject 

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- (void)setSomeProperty:(NSString *)someProperty{
    objc_setAssociatedObject(self, Key, @(quickTapEnable), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (NSString *)someProperty{
    return [objc_getAssociatedObject(self, Key) boolValue];
}

看了看之前写过的OC代码，微微一笑，写出了这段代码

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var refreshView : WaveView{
        set{
            objc_setAssociatedObject(self, "key", newValue, .OBJC_ASSOCIATION_COPY_NONATOMIC)
        }
        get{
            return objc_getAssociatedObject(self, "key") as! WaveView
        }
    }

1.png

然后用了一下这个这几行检验一下，果然没存进去。。。

我们看一下objc_setAssociatedObject 的API

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/** 
 * Sets an associated value for a given object using a given key and association policy.
 * 
 * @param object The source object for the association.
 * @param key The key for the association.
 * @param value The value to associate with the key key for object. Pass nil to clear an existing association.
 * @param policy The policy for the association. For possible values, see “Associative Object Behaviors.”
 * 
 * @see objc_setAssociatedObject
 * @see objc_removeAssociatedObjects
 */
@available(iOS 3.1, *)
public func objc_setAssociatedObject(_ object: Any!, _ key: UnsafeRawPointer!, _ value: Any!, _ policy: objc_AssociationPolicy)

第二个参数是UnsafeRawPointer结构体指针类型，Swift并不推荐对指针进行直接操作, 但仍提供了几种可以直接操作内存的指针类型，在Swift中无类型的指针，原始内存可以用UnsafeRawPointer 和UnsafeMutableRawPointer来表示

我们看一下UnsafeRawPointer 的构造函数

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/// Converts a pattern of bits to an `UnsafeRawPointer`.
///
/// Returns `nil` if `bitPattern` is zero.
public init?(bitPattern: Int)

/// Converts a pattern of bits to an `UnsafeRawPointer`.
///
/// Returns `nil` if `bitPattern` is zero.
public init?(bitPattern: UInt)

要想通过字符串生成意义对应的Int值，我们可以使用

"key".hashValue的形式将字符串生成哈希值来返回Int值

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var refreshView : WaveView? {
        set{
            let key: UnsafeRawPointer! = UnsafeRawPointer(bitPattern: "key".hashValue)
            objc_setAssociatedObject(self, key, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
        get{
            let key: UnsafeRawPointer! = UnsafeRawPointer(bitPattern: "key".hashValue)
            return objc_getAssociatedObject(self, key) as? WaveView
        }
    }

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这种方法完美解决了解包失败

因为是经常使用的key值，我们应该一次定义多次调用，避免这样重复写好多次,如同在配置文件里面定义全局通知的标识符一样

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let key = UnsafeRawPointer(bitPattern: "key".hashValue)

希望这篇文章可以帮到大家