57

UIButton 状态小结

 5 years ago
source link: https://www.tuicool.com/articles/uieUVfj
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.
neoserver,ios ssh client

我们先从一个问题说起，小明同学接到产品的一个新需求：实现一个 UIButton ，要求在 normal、selected、highlighted 三种状态下展示不同文案。这简直太简单了，小明同学1分钟不到就实现了，关键代码如下： 

[button setTitle:@"normal" forState:UIControlStateNormal];
[button setTitle:@"highlighted" forState:UIControlStateHighlighted];
[button setTitle:@"selected" forState:UIControlStateSelected];

这段代码有什么问题吗？

的确有问题！当 button 状态为 selected 时，点击按钮，文案展示 normal ，当前状态应该是 UIControlStateHighlighted ，怎么展示了 UIControlStateNormal 的文案？

问题分析

UIButton 有5种状态，分别是：default(normal), highlighted, focused, selected, disabled，通过属性 state 可以拿到当前状态值 UIControlState ，定义如下： 

@property(nonatomic,readonly) UIControlState state;                  // could be more than one state (e.g. disabled|selected). synthesized from other flags.

typedef NS_OPTIONS(NSUInteger, UIControlState) {
    UIControlStateNormal       = 0,
    UIControlStateHighlighted  = 1 << 0,                  // used when UIControl isHighlighted is set
    UIControlStateDisabled     = 1 << 1,
    UIControlStateSelected     = 1 << 2,                  // flag usable by app (see below)
    UIControlStateFocused NS_ENUM_AVAILABLE_IOS(9_0) = 1 << 3, // Applicable only when the screen supports focus
};

看到位运算我们就可以猜到这个状态可以组合，而且有句很关键的注释：

could be more than one state (e.g. disabled|selected). synthesized from other flags.

state 不是单独的状态，可以是多种状态的混合。

我们在回到上面的小明同学遇到的问题，当 button 状态为 selected 时，点击按钮，按钮此时的状态其实是 UIControlStateHighlighted | UIControlStateSelected 。在 官方文档 中，我们可以看到这么一句话： 

If a title is not specified for a state, the default behavior is to use the title associated with the UIControlStateNormal state

也就是说小明同学其实漏设置了一种状态，然后系统展示了按钮的默认状态 UIControlStateNormal ，按钮状态并不是是 UIControlStateNormal 。

小结

1、 UIControlState 是个组合状态，在 setTitle:forState: 、 setImage:forState: 时，如果需要自定义 UIControlStateSelected 状态，一定要注意自定义 UIControlStateHighlighted | UIControlStateSelected 。

2、如果按钮的当前状态没有自定义，使用 UIControlStateNormal 定义的值。


report

Recommend

About Joyk


Aggregate valuable and interesting links.
Joyk means Joy of geeK