MJRefresh 源码分析

https://github.com/CoderMJLee/MJRefresh

MJRefresh

一、MJRefreshComponent

#import <UIKit/UIKit.h>
#import "MJRefreshConst.h"
#import "UIView+MJExtension.h"
#import "UIScrollView+MJExtension.h"
#import "UIScrollView+MJRefresh.h"
#import "NSBundle+MJRefresh.h"

状态枚举

/** 刷新控件的状态 */
typedef NS_ENUM(NSInteger, MJRefreshState) {
    /** 普通闲置状态 */
    MJRefreshStateIdle = 1,
    /** 松开就可以进行刷新的状态 */
    MJRefreshStatePulling,
    /** 正在刷新中的状态 */
    MJRefreshStateRefreshing,
    /** 即将刷新的状态 */
    MJRefreshStateWillRefresh,
    /** 所有数据加载完毕，没有更多的数据了 */
    MJRefreshStateNoMoreData
};

刷新回调

#pragma mark - 刷新回调
/** 正在刷新的回调 */
@property (copy, nonatomic) MJRefreshComponentRefreshingBlock refreshingBlock;
/** 设置回调对象和回调方法 */
- (void)setRefreshingTarget:(id)target refreshingAction:(SEL)action;

/** 回调对象 */
@property (weak, nonatomic) id refreshingTarget;
/** 回调方法 */
@property (assign, nonatomic) SEL refreshingAction;
/** 触发回调（交给子类去调用） */
- (void)executeRefreshingCallback;

刷新状态控制

#pragma mark - 刷新状态控制
/** 进入刷新状态 */
- (void)beginRefreshing;
- (void)beginRefreshingWithCompletionBlock:(void (^)(void))completionBlock;
/** 开始刷新后的回调(进入刷新状态后的回调) */
@property (copy, nonatomic) MJRefreshComponentbeginRefreshingCompletionBlock beginRefreshingCompletionBlock;
/** 结束刷新的回调 */
@property (copy, nonatomic) MJRefreshComponentEndRefreshingCompletionBlock endRefreshingCompletionBlock;
/** 结束刷新状态 */
- (void)endRefreshing;
- (void)endRefreshingWithCompletionBlock:(void (^)(void))completionBlock;
/** 是否正在刷新 */
@property (assign, nonatomic, readonly, getter=isRefreshing) BOOL refreshing;
//- (BOOL)isRefreshing;
/** 刷新状态 一般交给子类内部实现 */
@property (assign, nonatomic) MJRefreshState state;

具体方法

- (void)beginRefreshing
{
    [UIView animateWithDuration:MJRefreshFastAnimationDuration animations:^{
        self.alpha = 1.0;
    }];
    self.pullingPercent = 1.0;
    // 只要正在刷新，就完全显示
    if (self.window) {
        self.state = MJRefreshStateRefreshing;
    } else {
        // 预防正在刷新中时，调用本方法使得header inset回置失败
        if (self.state != MJRefreshStateRefreshing) {
            self.state = MJRefreshStateWillRefresh;
            // 刷新(预防从另一个控制器回到这个控制器的情况，回来要重新刷新一下)
            [self setNeedsDisplay];
        }
    }
}

上面做了个动画效果，多加了一个willRefresh的状态， 为了防止self.window为空的时候，突然刷新崩溃（从另外一个页面返回的时候），所以需要一个状态来过度

设置state 然后调用 setNeedsDisplay方法；如果self.window为空，把状态改成即将刷新，并调用setNeedsDisplay

首先UIView的setNeedsDisplay 和setNeedsLayout方法都是异步执行的。而setNeedsDisplay会调用自动调用drawRect方法，这样可以拿到UIGraphicsGetCurrentContext， 就可以绘制了，而setNeedsLayout会默认调用layoutSubViews，就可以处理子视图中的一些数据。

综上所诉，setNeedsDisplay方便绘图，而layoutSubViews方便出来数据。

//结束刷新
- (void)endRefreshing
{
    __weak typeof(self) weakSelf = self;
    dispatch_async(dispatch_get_main_queue(), ^{
        weakSelf.state = MJRefreshStateIdle;
    });
}

在主线程结束刷新，把刷新状态改为普通闲置状态

KVO监听

#pragma mark - KVO监听
- (void)addObservers
{
    NSKeyValueObservingOptions options = NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld;
    [self.scrollView addObserver:self forKeyPath:MJRefreshKeyPathContentOffset options:options context:nil];
    [self.scrollView addObserver:self forKeyPath:MJRefreshKeyPathContentSize options:options context:nil];
    self.pan = self.scrollView.panGestureRecognizer;
    [self.pan addObserver:self forKeyPath:MJRefreshKeyPathPanState options:options context:nil];
}

- (void)removeObservers
{
    [self.superview removeObserver:self forKeyPath:MJRefreshKeyPathContentOffset];
    [self.superview removeObserver:self forKeyPath:MJRefreshKeyPathContentSize];
    [self.pan removeObserver:self forKeyPath:MJRefreshKeyPathPanState];
    self.pan = nil;
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    // 遇到这些情况就直接返回
    if (!self.userInteractionEnabled) return;
    
    // 这个就算看不见也需要处理
    if ([keyPath isEqualToString:MJRefreshKeyPathContentSize]) {
        [self scrollViewContentSizeDidChange:change];
    }
    
    // 看不见
    if (self.hidden) return;
    if ([keyPath isEqualToString:MJRefreshKeyPathContentOffset]) {
        [self scrollViewContentOffsetDidChange:change];
    } else if ([keyPath isEqualToString:MJRefreshKeyPathPanState]) {
        [self scrollViewPanStateDidChange:change];
    }
}

- (void)scrollViewContentOffsetDidChange:(NSDictionary *)change{}
- (void)scrollViewContentSizeDidChange:(NSDictionary *)change{}
- (void)scrollViewPanStateDidChange:(NSDictionary *)change{}

监听ContentOffset、ContentSize、手势的State

内部方法

#pragma mark - 内部方法
- (void)executeRefreshingCallback
{
    dispatch_async(dispatch_get_main_queue(), ^{
        if (self.refreshingBlock) {
            self.refreshingBlock();
        }
        if ([self.refreshingTarget respondsToSelector:self.refreshingAction]) {
            MJRefreshMsgSend(MJRefreshMsgTarget(self.refreshingTarget), self.refreshingAction, self);
        }
        if (self.beginRefreshingCompletionBlock) {
            self.beginRefreshingCompletionBlock();
        }
    });
}

MJRefreshMsgSend是时运行时objc_msgSend，第一个参数代表接收者，第二个参数代表选择子（SEL是选择子的类型），后续参数就是消息中的那些参数，其顺序不变。选择子指的就是方法的名字。

二、MJRefreshHeader

1、初始化（构造方法）

#pragma mark - 构造方法
+ (instancetype)headerWithRefreshingBlock:(MJRefreshComponentRefreshingBlock)refreshingBlock
{
    MJRefreshHeader *cmp = [[self alloc] init];
    cmp.refreshingBlock = refreshingBlock;
    return cmp;
}
+ (instancetype)headerWithRefreshingTarget:(id)target refreshingAction:(SEL)action
{
    MJRefreshHeader *cmp = [[self alloc] init];
    [cmp setRefreshingTarget:target refreshingAction:action];
    return cmp;
}

2、覆盖父类的方法

#pragma mark - 覆盖父类的方法
- (void)prepare
{
    [super prepare];
    
    // 设置key
    self.lastUpdatedTimeKey = MJRefreshHeaderLastUpdatedTimeKey;
    
    // 设置高度
    self.mj_h = MJRefreshHeaderHeight;
}

- (void)placeSubviews
{
    [super placeSubviews];
    
    // 设置y值(当自己的高度发生改变了，肯定要重新调整Y值，所以放到placeSubviews方法中设置y值)
    self.mj_y = - self.mj_h - self.ignoredScrollViewContentInsetTop;
}

prepare设置一下初始化值数据。而placeSubViews更新一下UI。

3、滚动时偏移值变化以及状态的改变

- (void)scrollViewContentOffsetDidChange:(NSDictionary *)change
{
    [super scrollViewContentOffsetDidChange:change];
    
    // 在刷新的refreshing状态
    if (self.state == MJRefreshStateRefreshing) {
        // 暂时保留
        if (self.window == nil) return;
        
        // sectionheader停留解决
        CGFloat insetT = - self.scrollView.mj_offsetY > _scrollViewOriginalInset.top ? - self.scrollView.mj_offsetY : _scrollViewOriginalInset.top;
        insetT = insetT > self.mj_h + _scrollViewOriginalInset.top ? self.mj_h + _scrollViewOriginalInset.top : insetT;
        self.scrollView.mj_insetT = insetT;
        
        self.insetTDelta = _scrollViewOriginalInset.top - insetT;
        return;
    }
    
    // 跳转到下一个控制器时，contentInset可能会变
    _scrollViewOriginalInset = self.scrollView.mj_inset;
    
    // 当前的contentOffset
    CGFloat offsetY = self.scrollView.mj_offsetY;
    // 头部控件刚好出现的offsetY
    CGFloat happenOffsetY = - self.scrollViewOriginalInset.top;
    
    // 如果是向上滚动到看不见头部控件，直接返回
    // >= -> >
    if (offsetY > happenOffsetY) return;
    
    // 普通 和 即将刷新 的临界点
    CGFloat normal2pullingOffsetY = happenOffsetY - self.mj_h;
    CGFloat pullingPercent = (happenOffsetY - offsetY) / self.mj_h;
    
    if (self.scrollView.isDragging) { // 如果正在拖拽
        self.pullingPercent = pullingPercent;
        if (self.state == MJRefreshStateIdle && offsetY < normal2pullingOffsetY) {
            // 转为即将刷新状态
            self.state = MJRefreshStatePulling;
        } else if (self.state == MJRefreshStatePulling && offsetY >= normal2pullingOffsetY) {
            // 转为普通状态
            self.state = MJRefreshStateIdle;
        }
    } else if (self.state == MJRefreshStatePulling) {// 即将刷新 && 手松开
        // 开始刷新
        [self beginRefreshing];
    } else if (pullingPercent < 1) {
        self.pullingPercent = pullingPercent;
    }
}

状态切换的因素有两个：一个是下拉的距离是否超过临界值，另一个是 手指是否离开屏幕。

手指还贴在屏幕的时候是不能进行刷新的。即使在下拉的距离超过了临界距离（状态栏 + 导航栏 + header高度），如果手指没有离开屏幕，那么也不能马上进行刷新，而是将状态切换为：可以刷新。一旦手指离开了屏幕，马上将状态切换为正在刷新。

4、改变状态时的相应操作（setter方法）

- (void)setState:(MJRefreshState)state
{
    MJRefreshCheckState
    //MJRefreshCheckState是宏，其实也就是下面语句，为了检测状态是否相同，相同则return
//    MJRefreshState oldState = self.state;
//    if (state == oldState) {
//        NSLog(@"相同");
//        return;
//    }
//    [super setState:state];

    
    // 根据状态做事情
    if (state == MJRefreshStateIdle) {
        if (oldState != MJRefreshStateRefreshing) return;
        
        // 保存刷新时间
        [[NSUserDefaults standardUserDefaults] setObject:[NSDate date] forKey:self.lastUpdatedTimeKey];
        [[NSUserDefaults standardUserDefaults] synchronize];
        
        // 恢复inset和offset
        [UIView animateWithDuration:MJRefreshSlowAnimationDuration animations:^{
            //此时要加上scrollView刷新时跟普通闲置时的偏移差值(刷新时偏移值为118或者142，self.insetTDelta值为header高度-54)，恢复后self.scrollView.mj_insetT = 64（或者88）
            self.scrollView.mj_insetT += self.insetTDelta;
            
            // 自动调整透明度
            if (self.isAutomaticallyChangeAlpha) self.alpha = 0.0;
        } completion:^(BOOL finished) {
            self.pullingPercent = 0.0;
            
            if (self.endRefreshingCompletionBlock) {
                self.endRefreshingCompletionBlock();
            }
        }];
    } else if (state == MJRefreshStateRefreshing) {
         dispatch_async(dispatch_get_main_queue(), ^{
            [UIView animateWithDuration:MJRefreshFastAnimationDuration animations:^{
                CGFloat top = self.scrollViewOriginalInset.top + self.mj_h;
                // 增加滚动区域top
                self.scrollView.mj_insetT = top;
                //增加滚动区域top(赋值给scrollView.inset.top)
                CGPoint offset = self.scrollView.contentOffset;
                offset.y = -top;
                [self.scrollView setContentOffset:offset animated:NO];
            } completion:^(BOOL finished) {
                //执行正在刷新的回调
                [self executeRefreshingCallback];
            }];
         });
    }
}

注意[super setState:state]的位置，等基类的state赋值给oldState，再跟新状态对比，对比完后，再[super setState:state]调用基类,从而赋值基类state

该方法主要要注意状态在普通闲置状态以及刷新状态的scrollView.contentOffset变化

三、MJRefreshStateHeader

该类是MJRefreshHeader的子类，主要用来设置显示上一次刷新时间的label：lastUpdatedTimeLabel和显示刷新状态的label：stateLabel属性等

1、stateLabel初始化方法

#pragma mark - 公共方法
- (void)setTitle:(NSString *)title forState:(MJRefreshState)state
{
    if (title == nil) return;
    self.stateTitles[@(state)] = title;
    self.stateLabel.text = self.stateTitles[@(self.state)];
}

#pragma mark - 覆盖父类的方法
- (void)prepare
{
    [super prepare];
    
    // 初始化间距
    self.labelLeftInset = MJRefreshLabelLeftInset;
    
    // 初始化文字
    [self setTitle:[NSBundle mj_localizedStringForKey:MJRefreshHeaderIdleText] forState:MJRefreshStateIdle];
    [self setTitle:[NSBundle mj_localizedStringForKey:MJRefreshHeaderPullingText] forState:MJRefreshStatePulling];
    [self setTitle:[NSBundle mj_localizedStringForKey:MJRefreshHeaderRefreshingText] forState:MJRefreshStateRefreshing];
}

prepare初始化方法，实现本地化（不同字体），并根据不同状态赋值给stateLabel

2、lastUpdatedLabel赋值

#pragma mark key的处理
- (void)setLastUpdatedTimeKey:(NSString *)lastUpdatedTimeKey
{
    [super setLastUpdatedTimeKey:lastUpdatedTimeKey];
    
    // 如果label隐藏了，就不用再处理
    if (self.lastUpdatedTimeLabel.hidden) return;
    
    NSDate *lastUpdatedTime = [[NSUserDefaults standardUserDefaults] objectForKey:lastUpdatedTimeKey];
    
    // 如果有block
    if (self.lastUpdatedTimeText) {
        self.lastUpdatedTimeLabel.text = self.lastUpdatedTimeText(lastUpdatedTime);
        return;
    }
    
    if (lastUpdatedTime) {
        // 1.获得年月日
        NSCalendar *calendar = [self currentCalendar];
        NSUInteger unitFlags = NSCalendarUnitYear| NSCalendarUnitMonth | NSCalendarUnitDay |NSCalendarUnitHour |NSCalendarUnitMinute;
        NSDateComponents *cmp1 = [calendar components:unitFlags fromDate:lastUpdatedTime];
        NSDateComponents *cmp2 = [calendar components:unitFlags fromDate:[NSDate date]];
        
        // 2.格式化日期
        NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
        BOOL isToday = NO;
        if ([cmp1 day] == [cmp2 day]) { // 今天
            formatter.dateFormat = @" HH:mm";
            isToday = YES;
        } else if ([cmp1 year] == [cmp2 year]) { // 今年
            formatter.dateFormat = @"MM-dd HH:mm";
        } else {
            formatter.dateFormat = @"yyyy-MM-dd HH:mm";
        }
        NSString *time = [formatter stringFromDate:lastUpdatedTime];
        
        // 3.显示日期
        self.lastUpdatedTimeLabel.text = [NSString stringWithFormat:@"%@%@%@",
                                          [NSBundle mj_localizedStringForKey:MJRefreshHeaderLastTimeText],
                                          isToday ? [NSBundle mj_localizedStringForKey:MJRefreshHeaderDateTodayText] : @"",
                                          time];
    } else {
        self.lastUpdatedTimeLabel.text = [NSString stringWithFormat:@"%@%@",
                                          [NSBundle mj_localizedStringForKey:MJRefreshHeaderLastTimeText],
                                          [NSBundle mj_localizedStringForKey:MJRefreshHeaderNoneLastDateText]];
    }
}

MJRefreshNormalHeader和MJRefreshGifHeader都是MJRefreshStateHeader的子类，前者和后者的布局一样，不同的就是header左边一个是菊花的样式，另外一个是gif，详看下图：

由此看来，这两种形式的header都有相同的共性，我们在做类似的功能时，如果有几个控件或者几个类共性一样，比如说，一个保险类（InsuranceClass），一个房地产类（RealEstateClass），他们可以有一个基类销售类（SalesClass），SalesClass拥有销售员工、顾客、金额、销售日期等 保险类 和 房地产类 需要的共同属性

四、MJRefreshNormalHeader

• 1、在MJRefreshStateHeader上添加了箭头和菊花
• 2、布局这两种样式View,且在状态切换时更改样式切换

1、圈圈（菊花）和箭头的布局

- (void)placeSubviews
{
    [super placeSubviews];
    
    // 箭头的中心点
    CGFloat arrowCenterX = self.mj_w * 0.5;
    if (!self.stateLabel.hidden) {
        CGFloat stateWidth = self.stateLabel.mj_textWith;
        CGFloat timeWidth = 0.0;
        if (!self.lastUpdatedTimeLabel.hidden) {
            timeWidth = self.lastUpdatedTimeLabel.mj_textWith;
        }
        CGFloat textWidth = MAX(stateWidth, timeWidth);
        arrowCenterX -= textWidth / 2 + self.labelLeftInset;
    }
    CGFloat arrowCenterY = self.mj_h * 0.5;
    CGPoint arrowCenter = CGPointMake(arrowCenterX, arrowCenterY);
    
    // 箭头
    if (self.arrowView.constraints.count == 0) {
        self.arrowView.mj_size = self.arrowView.image.size;
        self.arrowView.center = arrowCenter;
    }
        
    // 圈圈
    if (self.loadingView.constraints.count == 0) {
        self.loadingView.center = arrowCenter;
    }
    
    self.arrowView.tintColor = self.stateLabel.textColor;
}

上面代码主要实现了圈圈（菊花）和箭头的布局，需要注意的是让箭头菊花紧跟刷新文字或者状态文字居中的逻辑，

2、不同状态下菊花和箭头的互换

- (void)setState:(MJRefreshState)state
{
    MJRefreshCheckState
    
    // 根据状态做事情
    if (state == MJRefreshStateIdle) {
        if (oldState == MJRefreshStateRefreshing) { //上次状态是正在刷新，准备改变成普通闲置状态
            self.arrowView.transform = CGAffineTransformIdentity; //仿射变换初始化
            
            [UIView animateWithDuration:MJRefreshSlowAnimationDuration animations:^{
                self.loadingView.alpha = 0.0;  //把菊花变成完全透明
            } 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.backgroundColor = [UIColor greenColor];
                self.loadingView.alpha = 1.0; //菊花变成完全显示 （为什么要这样？求大佬告诉）
                [self.loadingView stopAnimating]; //菊花停止转动，同时会隐藏菊花（loadingView.hidesWhenStopped = YES;）
                self.arrowView.hidden = NO; //箭头显示
            }];
        } else { //上次状态是拖拽或者普通闲置状态，准备改变成普通闲置状态 --> 把菊花停止转动，菊花隐藏，箭头显示
            [self.loadingView stopAnimating];
            self.arrowView.hidden = NO;
            [UIView animateWithDuration:MJRefreshFastAnimationDuration animations:^{
                self.arrowView.transform = CGAffineTransformIdentity; //在操作结束之后对箭头设置量进行还原
            }];
        }
    } else if (state == MJRefreshStatePulling) { //拖拽状态：菊花停止转动，箭头显示
        [self.loadingView stopAnimating];
        self.arrowView.hidden = NO;
        [UIView animateWithDuration:MJRefreshFastAnimationDuration animations:^{
            self.arrowView.transform = CGAffineTransformMakeRotation(0.000001 - M_PI);//(改变箭头的方向，但是为什么要0.000001 - M_PI？)
        }];
    } else if (state == MJRefreshStateRefreshing) { //正在刷新状态：菊花完全显示并且开始转动，箭头隐藏
        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;
    }
}

通过不同的状态控制菊花和箭头的隐藏和消失，及他们的动画效果，如箭头的朝上朝下，和菊花的转与不转

四、MJRefreshGifHeader

1、加载不同状态对应的动画图片
2、设置不同状态对应的动画时间

懒加载

#pragma mark - 懒加载
- (UIImageView *)gifView
{
    if (!_gifView) { 
        UIImageView *gifView = [[UIImageView alloc] init]; 
        [self addSubview:_gifView = gifView]; 
    } 
    return _gifView; 
}

- (NSMutableDictionary *)stateImages 
{ 
    if (!_stateImages) { 
        self.stateImages = [NSMutableDictionary dictionary]; 
    } 
    return _stateImages; 
}

- (NSMutableDictionary *)stateDurations 
{ 
    if (!_stateDurations) { 
        self.stateDurations = [NSMutableDictionary dictionary]; 
    } 
    return _stateDurations; 
}

2、设置不通过状态对应的动画图片以及动画时间

#pragma mark - 公共方法
- (void)setImages:(NSArray *)images duration:(NSTimeInterval)duration forState:(MJRefreshState)state 
{ 
    if (images == nil) return; 
    
    self.stateImages[@(state)] = images; 
    self.stateDurations[@(state)] = @(duration); 
    
    /* 根据图片设置控件的高度 */ 
    UIImage *image = [images firstObject]; 
    if (image.size.height > self.mj_h) { 
        self.mj_h = image.size.height; 
    } 
}

- (void)setImages:(NSArray *)images forState:(MJRefreshState)state 
{ 
    [self setImages:images duration:images.count * 0.1 forState:state]; 
}

3、实现图片的切换和gifView布局

#pragma mark - 实现父类的方法
- (void)prepare
{
    [super prepare];
    
    // 初始化间距
    self.labelLeftInset = 20;
}

- (void)setPullingPercent:(CGFloat)pullingPercent
{
    [super setPullingPercent:pullingPercent];
    NSArray *images = self.stateImages[@(MJRefreshStateIdle)];
    if (self.state != MJRefreshStateIdle || images.count == 0) return;
    // 停止动画
    [self.gifView stopAnimating];
    // 设置当前需要显示的图片
    NSUInteger index =  images.count * pullingPercent;
    if (index >= images.count) index = images.count - 1;
    self.gifView.image = images[index];
}

- (void)placeSubviews
{
    [super placeSubviews];
    
    if (self.gifView.constraints.count) return;
    
    self.gifView.frame = self.bounds;
    if (self.stateLabel.hidden && self.lastUpdatedTimeLabel.hidden) {
        self.gifView.contentMode = UIViewContentModeCenter;
    } else {
        self.gifView.contentMode = UIViewContentModeRight;
        
        CGFloat stateWidth = self.stateLabel.mj_textWith;
        CGFloat timeWidth = 0.0;
        if (!self.lastUpdatedTimeLabel.hidden) {
            timeWidth = self.lastUpdatedTimeLabel.mj_textWith;
        }
        CGFloat textWidth = MAX(stateWidth, timeWidth);
        self.gifView.mj_w = self.mj_w * 0.5 - textWidth * 0.5 - self.labelLeftInset;
    }
}

- (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];
    }
}

到此，我对MJRefreshHeader那一块的源码已经读完，剩下MJRefreshFooter，但由于实现逻辑基本一致。