为什么我的 UIButton 没有被添加到我的单元格中？

Question

在我的cellForRowAtIndexPath: 方法中，我有以下代码：

        UIButton *signOutButton = [[UIButton alloc] init];

        [signOutButton addTarget:self action:@selector(logoutButtonTapped) forControlEvents:UIControlEventTouchUpInside];
        signOutButton.translatesAutoresizingMaskIntoConstraints = NO;
        signOutButton.titleLabel.textColor = [UIColor colorWithRed:0/255.0 green:180/255.0 blue:35/255.0 alpha:1.0];
        signOutButton.titleLabel.text = @"Sign Out";

        [cell.contentView addSubview:signOutButton];

        [cell.contentView addConstraint:[NSLayoutConstraint constraintWithItem:signOutButton
                                                                     attribute:NSLayoutAttributeLeading
                                                                     relatedBy:NSLayoutRelationEqual
                                                                        toItem:cell.contentView
                                                                     attribute:NSLayoutAttributeLeft
                                                                    multiplier:1.0
                                                                      constant:50.0]];

        [cell.contentView addConstraint:[NSLayoutConstraint constraintWithItem:signOutButton
                                                                     attribute:NSLayoutAttributeTrailing
                                                                     relatedBy:NSLayoutRelationEqual
                                                                        toItem:cell.contentView
                                                                     attribute:NSLayoutAttributeRight
                                                                    multiplier:1.0
                                                                      constant:50.0]];

        [cell.contentView addConstraint:[NSLayoutConstraint constraintWithItem:signOutButton
                                                                     attribute:NSLayoutAttributeBottom
                                                                     relatedBy:NSLayoutRelationEqual
                                                                        toItem:cell.contentView
                                                                     attribute:NSLayoutAttributeBottom
                                                                    multiplier:1.0
                                                                      constant:-6.0]];

但是当我加载单元格时它永远不会出现。我是 Auto Layout 的新手，所以谁能弄清楚我做错了什么？

奇怪的是，如果我点击按钮应该是方法执行的区域。

Answer 1

您的按钮正在添加，因为您的标签标题未设置，因此您看不到它。您可以更改背景颜色以查看它在单元格中的位置：

[signOutButton setBackgroundColor:[UIColor blueColor]];

然后改变标题和颜色如下：

[signOutButton setTitle:@"Sign Out" forState:UIControlStateNormal];
[signOutButton setTitleColor:[UIColor colorWithRed:0/255.0 green:180/255.0 blue:35/255.0 alpha:1.0] forState:UIControlStateNormal];

您的最终代码将如下所示：

    UIButton *signOutButton = [[UIButton alloc] init];

[signOutButton addTarget:self action:@selector(logoutButtonTapped) forControlEvents:UIControlEventTouchUpInside];
signOutButton.translatesAutoresizingMaskIntoConstraints = NO;
[signOutButton setTitle:@"Sign Out" forState:UIControlStateNormal];
[signOutButton setTitleColor:[UIColor colorWithRed:0/255.0 green:180/255.0 blue:35/255.0 alpha:1.0] forState:UIControlStateNormal];
[signOutButton setBackgroundColor:[UIColor blueColor]]; //just for testing, you can get rid of this line

[cell.contentView addSubview:signOutButton];

[cell.contentView addConstraint:[NSLayoutConstraint constraintWithItem:signOutButton
                                                             attribute:NSLayoutAttributeLeading
                                                             relatedBy:NSLayoutRelationEqual
                                                                toItem:cell.contentView
                                                             attribute:NSLayoutAttributeLeft
                                                            multiplier:1.0
                                                              constant:50.0]];

[cell.contentView addConstraint:[NSLayoutConstraint constraintWithItem:signOutButton
                                                             attribute:NSLayoutAttributeTrailing
                                                             relatedBy:NSLayoutRelationEqual
                                                                toItem:cell.contentView
                                                             attribute:NSLayoutAttributeRight
                                                            multiplier:1.0
                                                              constant:50.0]];

[cell.contentView addConstraint:[NSLayoutConstraint constraintWithItem:signOutButton
                                                             attribute:NSLayoutAttributeBottom
                                                             relatedBy:NSLayoutRelationEqual
                                                                toItem:cell.contentView
                                                             attribute:NSLayoutAttributeBottom
                                                            multiplier:1.0
                                                              constant:-6.0]];

Answer 2

由于该方法在您按下时执行，因此您的按钮似乎实际上已添加到单元格中。我认为标题没有设置。尝试更换 signOutButton.titleLabel.text = @"Sign Out" 和 [signOutButton setTitle:@"Sign Out" forState:UIControlStateNormal]