MJRefreshBackNormalFooter

添加箭头图片和刷新时的转动指示器

#pragma mark - 懒加载子控件
- (UIImageView *)arrowView
{
    if (!_arrowView) {
        UIImageView *arrowView = [[UIImageView alloc] initWithImage:[NSBundle mj_arrowImage]];
        [self addSubview:_arrowView = arrowView];
    }
    return _arrowView;
}


- (UIActivityIndicatorView *)loadingView
{
    if (!_loadingView) {
        UIActivityIndicatorView *loadingView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:self.activityIndicatorViewStyle];
        loadingView.hidesWhenStopped = YES;
        [self addSubview:_loadingView = loadingView];
    }
    return _loadingView;
}

- (void)setActivityIndicatorViewStyle:(UIActivityIndicatorViewStyle)activityIndicatorViewStyle
{
    _activityIndicatorViewStyle = activityIndicatorViewStyle;
    
    self.loadingView = nil;
    [self setNeedsLayout];
}
#pragma mark - 重写父类的方法
- (void)prepare
{
    [super prepare];
    
    self.activityIndicatorViewStyle = UIActivityIndicatorViewStyleGray;
}

- (void)placeSubviews
{
    [super placeSubviews];
    
    // 箭头的中心点
    CGFloat arrowCenterX = self.mj_w * 0.5;
    if (!self.stateLabel.hidden) {
        arrowCenterX -= self.labelLeftInset + self.stateLabel.mj_textWith * 0.5;
    }
    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;
}

- (void)setState:(MJRefreshState)state
{
    MJRefreshCheckState
    
    // 根据状态做事情
    if (state == MJRefreshStateIdle) {
        if (oldState == MJRefreshStateRefreshing) {
            self.arrowView.transform = CGAffineTransformMakeRotation(0.000001 - M_PI);
            [UIView animateWithDuration:MJRefreshSlowAnimationDuration animations:^{
                self.loadingView.alpha = 0.0;
            } completion:^(BOOL finished) {
                self.loadingView.alpha = 1.0;
                [self.loadingView stopAnimating];
                
                self.arrowView.hidden = NO;
            }];
        } else {
            self.arrowView.hidden = NO;
            [self.loadingView stopAnimating];
            [UIView animateWithDuration:MJRefreshFastAnimationDuration animations:^{
                self.arrowView.transform = CGAffineTransformMakeRotation(0.000001 - M_PI);
            }];
        }
    } else if (state == MJRefreshStatePulling) {
        self.arrowView.hidden = NO;
        [self.loadingView stopAnimating];
        [UIView animateWithDuration:MJRefreshFastAnimationDuration animations:^{
            self.arrowView.transform = CGAffineTransformIdentity;
        }];
    } else if (state == MJRefreshStateRefreshing) {
        self.arrowView.hidden = YES;
        [self.loadingView startAnimating];
    } else if (state == MJRefreshStateNoMoreData) {
        self.arrowView.hidden = YES;
        [self.loadingView stopAnimating];
    }
}

总结，使用到了transform来使用一张箭头图片进行旋转180度，是的有向上或向下的旋转效果