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在使用UIButton时，很多时候我们需要一个类似于- (void)setBackgroundColor:(UIColor *)color forState:(UIControlState)state这样的方法，来实现在不同的状态下使用不同的backgroundColor。遗憾的是，iOS默认并没有实现这个方法，那我们就自己来实现它。
让我们先来看看对于设置BackgroundImage，UIButton提供了如下方法：
- (void)setBackgroundImage:(UIImage *)image forState:(UIControlState)state UI_APPEARANCE_SELECTOR; // default is nil
- (UIImage *)backgroundImageForState:(UIControlState)state;
类似的，我们的函数实现声明如下：
- (void)setBackgroundColor:(UIColor *)color forState:(UIControlState)state;
- (UIColor *)backgroundColorForState:(UIControlState)state;
具体实现如下所示，代码很简单，不再赘述。
@interface WMButton : UIButton
@property (nonatomic, copy) NSString *name;
- (void)setBackgroundColor:(UIColor *)backgroundColor forState:(UIControlState)state;
- (UIColor *)backgroundColorForState:(UIControlState)state;
@end
@implementation WMButton
{
NSMutableDictionary *_colors;
}
- (instancetype)initWithFrame:(CGRect)frame
{
if (self = [super initWithFrame:frame]) {
_colors = [NSMutableDictionary dictionary];
}
return self;
}
- (void)setBackgroundColor:(UIColor *)backgroundColor forState:(UIControlState)state
{
// If it is normal then set the standard background here
if(state == UIControlStateNormal)
{
[super setBackgroundColor:backgroundColor];
}
// Store the background colour for that state
[_colors setValue:backgroundColor forKey:[self keyForState:state]];
}
- (UIColor *)backgroundColorForState:(UIControlState)state
{
return [_colors valueForKey:[self keyForState:state]];
}
- (void)setHighlighted:(BOOL)highlighted
{
// Do original Highlight
[super setHighlighted:highlighted];
// Highlight with new colour OR replace with orignial
NSString *highlightedKey = [self keyForState:UIControlStateHighlighted];
UIColor *highlightedColor = [_colors valueForKey:highlightedKey];
if (highlighted && highlightedColor) {
[super setBackgroundColor:highlightedColor];
} else {
// 由于系统在调用setSelected后，会再触发一次setHighlighted，故做如下处理，否则，背景色会被最后一次的覆盖掉。
if ([self isSelected]) {
NSString *selectedKey = [self keyForState:UIControlStateSelected];
UIColor *selectedColor = [_colors valueForKey:selectedKey];
[super setBackgroundColor:selectedColor];
} else {
NSString *normalKey = [self keyForState:UIControlStateNormal];
[super setBackgroundColor:[_colors valueForKey:normalKey]];
}
}
}
- (void)setSelected:(BOOL)selected
{
// Do original Selected
[super setSelected:selected];
// Select with new colour OR replace with orignial
NSString *selectedKey = [self keyForState:UIControlStateSelected];
UIColor *selectedColor = [_colors valueForKey:selectedKey];
if (selected && selectedColor) {
[super setBackgroundColor:selectedColor];
} else {
NSString *normalKey = [self keyForState:UIControlStateNormal];
[super setBackgroundColor:[_colors valueForKey:normalKey]];
}
}
- (NSString *)keyForState:(UIControlState)state
{
return [NSString stringWithFormat:@"state_%d", state];
}
@end使用时，如下调用即可：
[button setBackgroundColor:[UIColor clearColor] forState:UIControlStateNormal]; [button setBackgroundColor:[UIColor clearColor] forState:UIControlStateHighlighted]; [button setBackgroundColor:HotPinkColor forState:UIControlStateSelected];
需要注意的一点是，有些人可能会这样使用
[button setBackgroundColor:HotPinkColor forState:UIControlStateHighlighted | UIControlStateSelected];
这种用法是不被支持的，虽然可以实现，但是，其实对于iOS默认提供方法-
(void)setBackgroundImage:(UIImage *)image forState:(UIControlState)state UI_APPEARANCE_SELECTOR; // default is nil这种位于的用法也是不被完全支持的，大家可以试试看。
下面我们再来详细讨论下UIButton切换state的顺序问题。
当UIButton被按下时，会启动一个计时器，每隔一段时间，都会去检测按钮是否还处在被按下的状态。如果系统检测到它还处于被按下的状态，则就会切换到UIControlStateHighlighted，否则，恢复到UIControlStateNormal。当你长按后，在当前按钮的区域抬起手时，会切换到UIControlStateSelected，但是，需要注意的是，这次切换不仅会触发setSelected:被调用，也会触发setHighlighted:的一次调用。大家可以看看下面打印出来的Log。
2015-01-08 19:43:58.782 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.227 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.277 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.294 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.327 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.344 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.377 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.494 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.528 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.577 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.660 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.777 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.894 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.927 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:00.944 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:01.127 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:01.661 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:01.696 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:01.762 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:01.795 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:01.862 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:01.895 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:01.930 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:03.961 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:05.162 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:05.328 V |: highlighted = 1 @ WMButton(#38).-[WMButton setHighlighted:] 2015-01-08 19:44:05.346 V |: selected = 1 @ WMButton(#56).-[WMButton setSelected:] 2015-01-08 19:44:05.347 V |: highlighted = 0 @ WMButton(#38).-[WMButton setHighlighted:]