MJRefreshBackStateFooter

添加显示状态的label以及跟着状态的变化修改状态label上显示的文字

@implementation MJRefreshBackStateFooter
#pragma mark - 懒加载
- (NSMutableDictionary *)stateTitles
{
    if (!_stateTitles) {
        self.stateTitles = [NSMutableDictionary dictionary];
    }
    return _stateTitles;
}

- (UILabel *)stateLabel
{
    if (!_stateLabel) {
        [self addSubview:_stateLabel = [UILabel mj_label]];
    }
    return _stateLabel;
}

#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)];
}

- (NSString *)titleForState:(MJRefreshState)state {
  return self.stateTitles[@(state)];
}

#pragma mark - 重写父类的方法
- (void)prepare
{
    [super prepare];
    
    // 初始化间距
    self.labelLeftInset = MJRefreshLabelLeftInset;
    
    // 初始化文字
    [self setTitle:[NSBundle mj_localizedStringForKey:MJRefreshBackFooterIdleText] forState:MJRefreshStateIdle];
    [self setTitle:[NSBundle mj_localizedStringForKey:MJRefreshBackFooterPullingText] forState:MJRefreshStatePulling];
    [self setTitle:[NSBundle mj_localizedStringForKey:MJRefreshBackFooterRefreshingText] forState:MJRefreshStateRefreshing];
    [self setTitle:[NSBundle mj_localizedStringForKey:MJRefreshBackFooterNoMoreDataText] forState:MJRefreshStateNoMoreData];
}

- (void)placeSubviews
{
    [super placeSubviews];
    
    if (self.stateLabel.constraints.count) return;
    
    // 状态标签
    self.stateLabel.frame = self.bounds;
}

// 根据状态的变化，修改状态文字
- (void)setState:(MJRefreshState)state
{
    MJRefreshCheckState
    
    // 设置状态文字
    self.stateLabel.text = self.stateTitles[@(state)];
}
@end

总结：这种把没一个子模块子功能单独设计成一个类，是的结构清晰，非常干净整洁，但有一些缺点，如果读源码的人从子类读到父类，会有一大堆方法在父类，一个个网上找，会很麻烦，这种如果对源码了解会觉得很清晰，如果对源码不了解，会觉得很复杂繁琐