MJRefresh源码阅读(四)

上一篇[MJRefresh源码阅读（三）]（https://www.jianshu.com/p/ad830ae7694d）介绍了MJRefreshStateHeader类，这次介绍MJRefreshNormalHeader,这是默认的下拉刷新控件，继承于MJRefreshStateHeader。
这里比较简单，主要就是在重写的父类的setState中添加操作，改变箭头和加载的菊花标志,相关的代码为:

- (void)setState:(MJRefreshState)state {
    MJRefreshCheckState
    
    // 根据状态做事情
    if (state == MJRefreshStateIdle) {
        if (oldState == MJRefreshStateRefreshing) {
            self.arrowView.transform = CGAffineTransformIdentity;
            
            [UIView animateWithDuration:MJRefreshSlowAnimationDuration animations:^{
                self.loadingView.alpha = 0.0;
            } completion:^(BOOL finished) {
                // 如果执行完动画发现不是idle状态，就直接返回，进入其他状态
                if (self.state != MJRefreshStateIdle) return;
                
                self.loadingView.alpha = 1.0;
                [self.loadingView stopAnimating];
                self.arrowView.hidden = NO;
            }];
        } else {
            [self.loadingView stopAnimating];
            self.arrowView.hidden = NO;
            [UIView animateWithDuration:MJRefreshFastAnimationDuration animations:^{
                self.arrowView.transform = CGAffineTransformIdentity;
            }];
        }
    } else if (state == MJRefreshStatePulling) {
        [self.loadingView stopAnimating];
        self.arrowView.hidden = NO;
        [UIView animateWithDuration:MJRefreshFastAnimationDuration animations:^{
            self.arrowView.transform = CGAffineTransformMakeRotation(0.000001 - M_PI);
        }];
    } else if (state == MJRefreshStateRefreshing) {
        self.loadingView.alpha = 1.0; // 防止refreshing -> idle的动画完毕动作没有被执行
        [self.loadingView startAnimating];
        self.arrowView.hidden = YES;
    }
}

另外，和该文件并列的MJRefreshGifHeaderView是带动图的下拉刷新控件，同样是继承于MJRefreshStateHeader。
在该文件中，实现动态图使用的是UIImageView实现的动态图，UIImageView有个animationedImage属性，将一组图片数组赋予它，即可实现简单的动图效果.
相应的代码如下：

- (void)setState:(MJRefreshState)state
{
    MJRefreshCheckState
    
    // 根据状态做事情
    if (state == MJRefreshStatePulling || state == MJRefreshStateRefreshing) {
        NSArray *images = self.stateImages[@(state)];
        if (images.count == 0) return;
        
        [self.gifView stopAnimating];
        if (images.count == 1) { // 单张图片
            self.gifView.image = [images lastObject];
        } else { // 多张图片
            self.gifView.animationImages = images;
            self.gifView.animationDuration = [self.stateDurations[@(state)] doubleValue];
            [self.gifView startAnimating];
        }
    } else if (state == MJRefreshStateIdle) {
        [self.gifView stopAnimating];
    }
}