UIButton未显示

Question

我使用以下代码将UIButton和UITableView添加到UIViewController：

    self.tableView = ({
        UITableView *tableView = [[UITableView alloc] initWithFrame:CGRectZero style:UITableViewStylePlain];
        tableView.translatesAutoresizingMaskIntoConstraints = NO;
        tableView.scrollEnabled = NO;
        tableView.allowsSelection = NO;
        tableView.dataSource = self;
        tableView.delegate = self;
        tableView;
    });

    self.refreshButton = ({
        UIButton *button = [UIButton new];
        button.translatesAutoresizingMaskIntoConstraints = NO;
        [button setTitle:@"testtest" forState:UIControlStateNormal];
        [button addTarget:self
                   action:@selector(clickRefreshButton)
         forControlEvents:UIControlEventTouchUpInside];
        button.titleLabel.numberOfLines = 1;
        button.titleLabel.textAlignment = NSTextAlignmentRight;
        button.titleLabel.adjustsFontSizeToFitWidth = NO;
        button.alpha = 1.0;
        button;
    });

    [self.view addSubview:self.tableView];
    [self.view addSubview:self.refreshButton];
    CGFloat tableViewUpPadding = 20.0f;
    CGFloat navigationBarHeight = self.navigationController.navigationBar.frame.size.height;
    CGFloat tabBarHeight = self.tabBarController.tabBar.frame.size.height;
    CGFloat buttonOffset = 10.0f;
    CGFloat buttonSideLength = 50.0f;

    [self.tableView mas_makeConstraints:^(MASConstraintMaker *make){
        make.top.equalTo(self.view.mas_top).offset(tableViewUpPadding);
        make.bottom.equalTo(self.view.mas_bottom).offset(-tabBarHeight);
        make.width.equalTo(self.view.mas_width);
        make.left.equalTo(self.view.mas_left);
    }];

    [self.refreshButton mas_makeConstraints:^(MASConstraintMaker *make){
        make.right.equalTo(self.view.mas_right).offset(-buttonOffset);
        make.bottom.equalTo(self.view.mas_bottom).offset(-buttonOffset);
        make.width.equalTo(@(buttonSideLength));
        make.height.equalTo(@(buttonSideLength));
    }];

其中我使用砌体进行自动布局。但是，当我运行应用程序时，按钮不会出现，甚至在查看调试区域也没有。有人可以告诉我原因吗？

或者，如果我使用字符串和struts创建按钮，它仍然不会显示：（

CGRect applicationFrame = [UIScreen mainScreen].bounds;
CGFloat screenWidth = CGRectGetWidth(applicationFrame);
CGFloat screenHeight = CGRectGetHeight(applicationFrame);
CGFloat buttonWidth = 40.0f;
CGFloat buttonHeight = 40.0f;
CGFloat spacing = 10.0f;
CGFloat buttonX = screenWidth - buttonWidth - spacing;
CGFloat buttonY = screenHeight - buttonHeight - spacing;
CGRect buttonFrame = CGRectMake(buttonX, buttonY, buttonWidth, buttonHeight);
[self.refreshButton setFrame:buttonFrame];

顺便说一下，我发现如果我想使用自动布局更改self.tableView的宽度，那么它也是不可能的：

    [self.tableView mas_makeConstraints:^(MASConstraintMaker *make){
        make.top.equalTo(self.view.mas_top).offset(tableViewUpPadding);
        make.bottom.equalTo(self.view.mas_bottom).offset(-tabBarHeight);
        make.width.equalTo(self.view.as_width).offset(-offset);
        make.left.equalTo(self.view.mas_left);
    }];

事实证明，tableview仍然与self.view

一样宽