UITableView tableFooterView autolayout自动计算高度

    UIView *tableFooter = [UIView new];
    self.tableView.tableFooterView = tableFooter;
    
    UILabel *footerLabel = [UILabel new];
    footerLabel.numberOfLines = 0;
    footerLabel.backgroundColor = [UIColor redColor];
    [tableFooter addSubview:footerLabel];
    
　　//UITableView 不能给 tableFooterView添加约束，但可给其子view添加约束
    [footerLabel mas_makeConstraints:^(MASConstraintMaker *make) {
        make.edges.mas_equalTo(tableFooter).mas_offset([NSValue valueWithUIEdgeInsets:UIEdgeInsetsMake(10, 10, 10, 10)]);
    }];
    
    footerLabel.preferredMaxLayoutWidth = CGRectGetWidth([UIScreen mainScreen].bounds) - 20;
    footerLabel.text = @"[footerLabel mas_makeConstraints:^(MASConstraintMaker *make) {    make.edges.mas_equalTo(tableFooter).mas_offset([NSValue valueWithUIEdgeInsets:UIEdgeInsetsMake(10, 10, 10, 10)]);    }];";

    //计算tableFooterView的size
    CGSize size = [tableFooter systemLayoutSizeFittingSize:CGSizeMake([UIScreen mainScreen].bounds.size.width, 1000)];
    tableFooter.frame = CGRectMake(0, 0, size.width, size.height);
    self.tableView.tableFooterView = tableFooter;