UIButton實現setBackgroundColor:ForState功能

在使用UIButton時，很多時候我們需要一個類似於- (void)setBackgroundColor:(UIColor *)color forState:(UIControlState)state這樣的方法，來實現在不同的狀態下使用不同的backgroundColor。遺憾的是，iOS默認並沒有實現這個方法，那我們就自己來實現它。

讓我們先來看看對於設置BackgroundImage，UIButton提供瞭如下方法：

- (void)setBackgroundImage:(UIImage *)image forState:(UIControlState)state UI_APPEARANCE_SELECTOR; // default is nil
- (UIImage *)backgroundImageForState:(UIControlState)state;

類似的，我們的函數實現聲明如下：

- (void)setBackgroundColor:(UIColor *)color forState:(UIControlState)state;

- (UIColor *)backgroundColorForState:(UIControlState)state;

具體實現如下所示，代碼很簡單，

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@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 {
        // 由於系統在調用setSelected後，會再觸發一次setHighlighted，故做如下處理，否則，背景色會被最後一次的覆蓋掉。
        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

使用時，如下調用即可：

[button setBackgroundColor:[UIColor clearColor] forState:UIControlStateNormal];
[button setBackgroundColor:[UIColor clearColor] forState:UIControlStateHighlighted];
[button setBackgroundColor:HotPinkColor forState:UIControlStateSelected];