当没有数据时，设置一张背景图片提示无数据

#import "UIView+AutoLayout.h"

@property (nonatomic, weak) UIImageView *noDataView;


- (UIImageView *)noDataView
{
    if (!_noDataView) {
        // 添加一个"没有数据"的提醒
        UIImageView *noDataView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"icon_deals_empty"]];
        [self.view addSubview:noDataView];
        [noDataView autoCenterInSuperview];
        self.noDataView = noDataView;
    }
    return _noDataView;
}