这些设置在 Interface Builder 中有什么作用？

Question

This is for a UIButton specifically. I understand that the alignment options pertain to the label inside the UIButton , but what does the 'content' settings do? They seem like they correspond to the setEnabled: , setSelected: , setHighlighted: methods of the UIButton class, however clicking Highlighted or Selected doesn't seem to change the button's behavior outside of interface builder. Also, what would be the use-case for having a button always show highlighted or selected?

Answer 1

There are several practical uses for these methods. As @MHUMobileInc. pointed out, it can be used for a game like Minesweeper. It can also allow you to use the button as a sort of switch, where the selected button has "ON" and the non-selected version has "OFF". It seems that Apple wants developers to shy away from this, and to use either UISwitches or a custom view. However, Apple does contradict itself in some of its apps .

These settings set the initial state of the UIButton- so if in your viewDidLoad you set it not selected nor highlighted, this Interface Builder setting will not be seen on screen when you run the app. If you want to ensure that these settings are kept, it might be easier to say so in code ( viewDidLoad ) rather than Interface Builder.

It may be easier not to use these settings too much. They can lead to confusion for you (the developer), other programmers who are working on the project (if any) and the user. Use the built-in UIKit views when it works and create your own subclasses when there is nothing that fits best for the situation.

Answer 2

The upper portion addresses the alignment of the content within the view. For example, if you have a large UIButton with an image that's smaller than the bounds of the button, by default the image will be centered vertically and horizontally inside the button. However, if you want the image to hug the left/right/top/bottom, you can set the alignment using those options.

Answer 3

All of these controls pertain to the UIControl, not UIButton, as indicated by the header in that screenshot.

Alignment refers to contentHorizontalAlignment and contentVerticalAlignment . Many controls return a fixed width or fixed height, or both, from sizeThatFits: . For example a UISwitch object has a fixed size, whereas a UISlider object has a fixed height. If you assign a frame to a control object that does not correspond to these fixed dimensions, these properties determine where in that frame the control interface should be drawn. Instances of UIButton do fill their frame, so the UIButton class interprets these properties differently to apply to the button's content, but the properties themselves are not specific to the UIButton class.

Similarly the selected , highlighted and enabled properties are defined by UIControl not UIButton , not all subclasses of UIControl utilise them.