iOS 按钮左文右图

参考：https://www.jianshu.com/p/1d74cc10c8a7
一、
xib无效

button.semanticContentAttribute = UISemanticContentAttributeForceRightToLeft;

二、
设置titleEdgeInsets或imageEdgeInsets，需要frame确定后才能计算，或者自己用 boundingRectWithSize:options:attributes:context: 计算出title的size

button.titleEdgeInsets = UIEdgeInsetsMake(0, -button.imageView.frame.size.width, 0, button.imageView.frame.size.width);
button.imageEdgeInsets = UIEdgeInsetsMake(0, button.titleLabel.frame.size.width, 0, -button.titleLabel.frame.size.width);

三、
派生一个UIButton的子类，来实现titleEdgeInsets与imageEdgeInsets的自动更新。

- (void)layoutSubviews {
    [super layoutSubviews];
    [self updateEdgeInsets];
}

- (void)updateEdgeInsets {
    self.titleEdgeInsets = UIEdgeInsetsMake(0, -self.imageView.frame.size.width, 0, self.imageView.frame.size.width);
    self.imageEdgeInsets = UIEdgeInsetsMake(0, self.titleLabel.frame.size.width, 0, -self.titleLabel.frame.size.width);
}

四、
派生一个UIButton的子类，通过重载 titleRectForContentRect: 和 imageRectForContentRect: 来分别指定文本和图片的显示区域。

@interface FCReverseButton ()

@property (nonatomic, assign) CGRect originalImageRect; // 原图片区域
@property (nonatomic, assign) CGRect originalTitleRect; // 原文本区域

@end

@implementation FCReverseButton

- (CGRect)titleRectForContentRect:(CGRect)contentRect {
    if (CGRectIsEmpty(self.originalTitleRect)) {
        self.originalTitleRect = [super titleRectForContentRect:contentRect];
    }

    if (CGRectIsEmpty(self.originalTitleRect) || CGRectIsEmpty(self.originalImageRect)) {
        return self.originalTitleRect;
    } else {
        CGFloat height = MAX(CGRectGetHeight(self.originalTitleRect), CGRectGetHeight(self.originalImageRect));
        return CGRectMake(contentRect.origin.x + self.titleEdgeInsets.right, contentRect.origin.y + (height - CGRectGetHeight(self.originalTitleRect)) / 2, CGRectGetWidth(self.originalTitleRect), CGRectGetHeight(self.originalTitleRect));
    }
}

- (CGRect)imageRectForContentRect:(CGRect)contentRect {
    if (CGRectIsEmpty(self.originalImageRect)) {
        self.originalImageRect = [super imageRectForContentRect:contentRect];
    }

    if (CGRectIsEmpty(self.originalTitleRect) || CGRectIsEmpty(self.originalImageRect)) {
        return self.originalImageRect;
    } else {
        CGFloat height = MAX(CGRectGetHeight(self.originalTitleRect), CGRectGetHeight(self.originalImageRect));
        return CGRectMake(contentRect.origin.x + CGRectGetWidth(self.originalTitleRect) + self.imageEdgeInsets.right, contentRect.origin.y + (height - CGRectGetHeight(self.originalImageRect)) / 2, CGRectGetWidth(self.originalImageRect), CGRectGetHeight(self.originalImageRect));
    }
}

@end

五、
在坐标系的层面翻转按钮的X轴，再分别将titleLabel和imageView的X轴翻转回来。可以直接对UIButton进行操作，也可以派生一个子类。

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        [self horizontalReverse];
    }
    return self;
}

- (instancetype)initWithCoder:(NSCoder *)aDecoder {
    self = [super initWithCoder:aDecoder];
    if (self) {
        [self horizontalReverse];
    }
    return self;
}

// 水平翻转
- (void)horizontalReverse {
    self.transform = CGAffineTransformMakeScale(-1, 1);
    self.imageView.transform = CGAffineTransformMakeScale(-1, 1);
    self.titleLabel.transform = CGAffineTransformMakeScale(-1, 1);
}