Xcode 4 和 Interface Builder：编辑垂直间距约束（锚定顶部，而不是底部）

Xcode 4 and Interface Builder: Editing Vertical Spacing Constraint (Anchor Top, not Bottom)

提问by jww

I've got a widget that is not laying out correctly on device (its looksOK in IB, but its not quite right). The widget is a label and its located about mid-screen. Interface Builder gave it a Vertical Space Constraint with a 'Bottom Anchor'. Here, bottom means bottom of the screen (rather than a widget below, or anchor to top screen).

我有一个小部件在设备上没有正确布局（它在 IB 中看起来不错，但不太正确）。小部件是一个标签，它位于屏幕中间。Interface Builder 给了它一个带有“底部锚点”的垂直空间约束。在这里，底部意味着屏幕的底部（而不是下面的小部件，或锚定到顶部屏幕）。

I'm in the inspector, but I don't see how to change to a top anchor (preferably, to the widget above). I tried reading Apple's docsand Editing Constraintsin particular, but it was a confusing and did not explain how to make the change (or I missed the discussion - which was 7 sentences).

我在检查员中，但我不知道如何更改为顶部锚点（最好是上面的小部件）。我尝试阅读 Apple 的文档和特别是Editing Constraints，但它令人困惑并且没有解释如何进行更改（或者我错过了讨论 - 这是 7 句话）。

Below is a screen capture under Interface Builder showing the Vertical Space Constraint anchored to the bottom of the screen. And its attributes leave a lot to be desired - Equal, Constant and Priority don't really help.

下面是 Interface Builder 下的屏幕截图，显示了锚定到屏幕底部的垂直空间约束。它的属性还有很多不足之处——平等、恒定和优先级并没有真正的帮助。

Does anyone know how to edit constraints? Specifically, I want to (1) change a vertical spacer's anchor from bottom totop; and (2) anchor against the widget above, and not the top of the screen.

有谁知道如何编辑约束？具体来说，我想（1）从下到上改变垂直间隔的锚点；(2) 锚定在上面的小部件上，而不是屏幕顶部。

回答by jrturton

Select the "Embedded" and the "Calculated" element together by shift-clicking.

通过按住 Shift 键单击一起选择“Embedded”和“Calculated”元素。

With those two elements selected, use the constraints menu:

选择这两个元素后，使用约束菜单：

This menu, together with careful selection of elements, is central to happy editing of constraints in IB. In your case, choose the central item, the Pin menu. Choose Vertical Spacing - this will create a new constraint on vertical spacing between your two elements. Alternatively, select a single element and pin "Top space to superview" to pin to the top instead of the bottom.

该菜单与精心选择的元素一起，是在 IB 中愉快地编辑约束的核心。在您的情况下，选择中心项目，Pin 菜单。选择垂直间距 - 这将在两个元素之间的垂直间距上创建一个新约束。或者，选择单个元素并将“顶部空间到超级视图”固定到顶部而不是底部。

You can now select and delete the vertical spacing to the bottom of the view. IB wouldn't let you delete this before since you have to have a complete, non-ambiguous set of constraints. After adding your new vertical spacing constraint, you now have this.

您现在可以选择并删除到视图底部的垂直间距。IB 不会让您在此之前删除它，因为您必须拥有一组完整的、明确的约束。添加新的垂直间距约束后，您现在拥有了这个。

To illustrate further, here is an empty view controller, with a single text field which I have dragged on:

为了进一步说明，这里是一个空的视图控制器，我拖了一个文本字段：

All of the constraints are purple, which means IB has added them for me (they are System constraints) and they can't be removed - they are the minimum constraints needed to position and size the text field.

所有的约束都是紫色的，这意味着 IB 已经为我添加了它们（它们是系统约束）并且它们不能被删除——它们是定位和调整文本字段大小所需的最小约束。

Now, I'll select the text field, and pin the top space to the superview:

现在，我将选择文本字段，并将顶部空间固定到超级视图：

Now you can see that the two vertical space constraints have changed to blue (they are now user constraints) and they have a thicker appearance in the editor. This means that one of them can be deleted. I select the constraint for the bottom space and hit delete:

现在您可以看到两个垂直空间约束已更改为蓝色（它们现在是用户约束）并且它们在编辑器中的外观更厚。这意味着可以删除其中之一。我选择底部空间的约束并点击删除：

Note that this still has the appearance of a user constraint - but if I try to delete it, IB will automatically recreate the system constraint pinning to the bottom of the superview, getting us back to square one.

请注意，这仍然具有用户约束的外观 - 但如果我尝试删除它，IB 将自动重新创建固定到超级视图底部的系统约束，让我们回到原点。

I have written about this, and similar autolayout topics, here.

我已经写过这个和类似的自动布局主题，这里。

回答by zyzzyxx

I got one word for Autolayouts. If it works, it works but if it does not, then use the old fashioned way (use code)

我对自动布局有一个词。如果有效，则有效，但如果无效，则使用老式方法（使用代码）