需求

在某些时候，需要对请求进行延时处理。
例如：

• 对某条评论进行点赞，如果用户无限点击赞/取消赞按钮，就会无限发出请求。这是一种不合理的做法。通常采用一种折中的办法，在点击按钮一段时候(例如1秒)后才真正发出请求。

ScreenShot_20161110150104.png

例如:在切换不同Tab时候要调用不同的API

ScreenShot_20161110150508.png

解决方案

• 在UI层面，添加一个分类

/**
 *  @brief 在 delay秒之后，执行action操作
 *
 *  @param action    执行的操作
 *  @param newObject 参数
 *  @param delay     延时时间
 */
-(void)debounceAction:(SEL)action object:(id)newObject delay:(NSTimeInterval)delay;

实现

+(void)debounceForTarget:(id)target action:(SEL)action object:(id)newObject delay:(NSTimeInterval)delay{
    
    if(target == nil || action == nil){ return;}
    
    // NSString *selectorString = NSStringFromSelector(action);
    // id oldObj = objc_getAssociatedObject(target,[selectorString UTF8String]); // WRONG
    id oldObj = objc_getAssociatedObject(target,action);
    //NSLog(@"oldObj:%@",oldObj);
    [NSObject cancelPreviousPerformRequestsWithTarget:target selector:action object:oldObj];
    
    // Why do we need to retain this object???
    objc_setAssociatedObject(target, action, newObject, OBJC_ASSOCIATION_RETAIN);
    
    // NSString *selectorString2 = NSStringFromSelector(action);
    // id newObj = objc_getAssociatedObject(target,[selectorString2 UTF8String]);
    
    //id newObj = objc_getAssociatedObject(target,@selector(action));
    //NSLog(@"newObj:%@",newObj);
    [target performSelector:action withObject:newObject afterDelay:delay];
    
}

-(void)debounceAction:(SEL)action object:(id)newObject delay:(NSTimeInterval)delay{
    [[self class] debounceForTarget:self action:action object:newObject delay:delay];
}


+(void)debounceForTarget:(id)target action:(SEL)action objectToBeCancelled:(id)oldObject objectToBePerform:(id)newObject delay:(NSTimeInterval)delay{
    
    NSAssert(target != nil, @"target 不能为nil", nil);
    
    // !!! call this method may cancel other actions ,
    //[NSObject cancelPreviousPerformRequestsWithTarget:target];
    
    [NSObject cancelPreviousPerformRequestsWithTarget:target selector:action object:oldObject];
    
    //    [NSObject cancelPreviousPerformRequestsWithTarget:target selector:action object:object];
    //  the Argument [object] may be different with last performrequest,if so,the last perform will not be cancelled. 
    [target performSelector:action withObject:newObject afterDelay:delay];
    
}

Demo

别人的gitNSObject-DebounceDemo.

• 在http request里增加time之类的想法，改动便捷性都不合适。