曾在网上看到过一个这样的文章iOS防止UIButton重复点击的三种实现方式,其中利用runtime来解决问题的思路很高端，但是使用过程中会碰到unrecognized selector sent to instance的问题。下面来解释产生这个问题的原因。
源代码:
UIButton+TdxNoRepeatButton.h
#import <UIKit/UIKit.h>
@interface UIButton (TdxNoRepeatButton)
@property (nonatomic, assign) NSTimeInterval tdx_acceptEventInterval; // 重复点击的间隔
@end
UIButton+TdxNoRepeatButton.m
#import "UIButton+TdxNoRepeatButton.h"
#import <objc/runtime.h>
// 因category不能添加属性，只能通过关联对象的方式。
static const char *UIControl_acceptEventInterval = "UIControl_acceptEventInterval";
static const char *UIControl_acceptEventTime = "UIControl_acceptEventTime";
@interface UIButton (TdxNoRepeatButton)
@property (nonatomic, assign,) NSTimeInterval tdx_acceptEventTime; //当前点击时间
@end
@implementation UIButton (TdxNoRepeatButton)
- (NSTimeInterval)tdx_acceptEventInterval {
return [objc_getAssociatedObject(self, UIControl_acceptEventInterval) doubleValue];
}
- (void)setTdx_acceptEventInterval:(NSTimeInterval)tdx_acceptEventInterval {
objc_setAssociatedObject(self, UIControl_acceptEventInterval, @(tdx_acceptEventInterval), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (NSTimeInterval)tdx_acceptEventTime {
return [objc_getAssociatedObject(self, UIControl_acceptEventTime) doubleValue];
}
- (void)setTdx_acceptEventTime:(NSTimeInterval)tdx_acceptEventTime {
objc_setAssociatedObject(self, UIControl_acceptEventTime, @(tdx_acceptEventTime), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
// 在load时执行hook
+ (void)load {
Method before = class_getInstanceMethod(self, @selector(sendAction:to:forEvent:));
Method after = class_getInstanceMethod(self, @selector(tdx_sendAction:to:forEvent:));
method_exchangeImplementations(before, after);
}
- (void)tdx_sendAction:(SEL)action to:(id)target forEvent:(UIEvent *)event {
if ([NSDate date].timeIntervalSince1970 - self.tdx_acceptEventTime < self.tdx_acceptEventInterval) {
return;
}
if (self.tdx_acceptEventInterval > 0) {
self.tdx_acceptEventTime = [NSDate date].timeIntervalSince1970;
}
[self tdx_sendAction:action to:target forEvent:event];
}
@end
unrecognized selector产生的原因
我们在利用这个UIButton的Category时，如若遇到UITabBarButton、UISegmentedControl继承自UIControl的类就会产生崩溃，因为这些类并没有实现tdx_sendAction:to:forEvent函数。为什么会出现这种情况呢，我们明明是对UIButton进行Category扩展。首先我们来看看class_getInstanceMethod函数说明:
/**
* Returns a specified instance method for a given class.
*
* @param cls The class you want to inspect.
* @param name The selector of the method you want to retrieve.
*
* @return The method that corresponds to the implementation of the selector specified by
* \e name for the class specified by \e cls, or \c NULL if the specified class or its
* superclasses do not contain an instance method with the specified selector.
*
* @note This function searches superclasses for implementations, whereas \c class_copyMethodList does not.
*/
OBJC_EXPORT Method class_getInstanceMethod(Class cls, SEL name)
OBJC_AVAILABLE(10.0, 2.0, 9.0, 1.0);
注意note里面的话，这个函数会搜索父类的实现，而我们需要hook的函数正好是在UIControl中实现的，而不是UIButton,所以此处会hook所有的UIControl的sendAction:to:forEvent:函数。继而UITabBarButton、UISegmentedControl继承自UIControl的类都会被hook到，因此才会产生unrecognized selector错误。
解决方案
既然知道产生问题的原因，那么下面我们来解决这个问题，有两种解决方案。
1、从UIControl入手。我们要hook的函数来自UIControl，那么我们可以为UIControl添加Category，而不是UIButton，这样所有继承自UIControl的类都会添加这个Category。
2、修改hook实现。修改load函数后的实现如下：
+ (void)load {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
Class class = [self class];
SEL originalSelector = @selector(sendAction:to:forEvent:);
SEL swizzledSelector = @selector(tdx_sendAction:to:forEvent:);
Method originalMethod = class_getInstanceMethod(class, originalSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
BOOL success = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
if (success) {
class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
} else {
method_exchangeImplementations(originalMethod, swizzledMethod);
}
});
}
简单说下上述实现的思路。首先取到class、originalSelector、swizzledSelector、originalMethod、swizzledMethod，然后利用class_addMethod这个函数，此函数文档如下：
/**
* Adds a new method to a class with a given name and implementation.
*
* @param cls The class to which to add a method.
* @param name A selector that specifies the name of the method being added.
* @param imp A function which is the implementation of the new method. The function must take at least two arguments—self and _cmd.
* @param types An array of characters that describe the types of the arguments to the method.
*
* @return YES if the method was added successfully, otherwise NO
* (for example, the class already contains a method implementation with that name).
*
* @note class_addMethod will add an override of a superclass's implementation,
* but will not replace an existing implementation in this class.
* To change an existing implementation, use method_setImplementation.
*/
OBJC_EXPORT BOOL class_addMethod(Class cls, SEL name, IMP imp,
const char *types)
OBJC_AVAILABLE(10.5, 2.0, 9.0, 1.0);
这个函数会在当前类上添加一个实例方法，并覆盖父类的方法返回YES。如果当前类有这个方法则无法覆盖返回NO。而我们hook的实现返回NO才会使用method_exchangeImplementations交换两者实现，这样有效的避免了替换掉当前类并未实现而在父类实现的方法，而所引发的unrecognized selector问题。