ios - 尝试使用自动布局将 UIButton 添加到我的视图中，但它没有出现。为什么？

Question

我有以下代码：

- (void)addLogoutButton {
    UIButton *logoutButton = [[UIButton alloc] init];
    logoutButton.translatesAutoresizingMaskIntoConstraints = NO;
    [logoutButton setTitle:@"Logout" forState:UIControlStateNormal];
    [self.view addSubview:logoutButton];

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:logoutButton
                                                 attribute:NSLayoutAttributeTop
                                                 relatedBy:NSLayoutRelationEqual
                                                 toItem:self.view
                                                 attribute:NSLayoutAttributeTop
                                                 multiplier:1.0
                                                 constant:-100.0]];

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:logoutButton
                                                 attribute:NSLayoutAttributeLeft
                                                 relatedBy:NSLayoutRelationEqual
                                                 toItem:self.view
                                                 attribute:NSLayoutAttributeLeft
                                                 multiplier:1.0
                                                 constant:40.0]];


    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:logoutButton
                                                 attribute:NSLayoutAttributeRight
                                                 relatedBy:NSLayoutRelationEqual
                                                 toItem:self.view
                                                 attribute:NSLayoutAttributeRight
                                                 multiplier:1.0
                                                 constant:-40]];
}

但是当我运行该应用程序时，找不到该按钮。为什么是这样？

Answer 1

将您的第一个约束常量更改为+100.0并使用以下命令初始化您的按钮：

[UIButton buttonWithType:UIButtonTypeRoundedRect];