1.为什么要写这样一个分类？
在应用开发过程中，我们经常需要设置Label之间的行间距，以及字间距，每次都是复制粘贴代码，为了摆脱这种累赘，怎么才能在需要的时候只需要调用一次代码就可以实现呢？因此就有了下面的代码：
2.实现原理
为UILabel写了一个分类，UILabel+SNExtension,在头文件中，就添加两个属性。
/**
* 设置行间距
*/
@property (nonatomic, assign) CGFloat sn_lineSpace;
/**
* 设置字体之间的间距
*/
@property (nonatomic, assign) CGFloat sn_wordSpace;
在私有方法中，
#pragma mark - 利用Runtime为分类添加属性
- (CGFloat)sn_lineSpace
{
return [objc_getAssociatedObject(self, _cmd) floatValue];
}
- (void)setSn_lineSpace:(CGFloat)sn_lineSpace
{
objc_setAssociatedObject(self, @selector(sn_lineSpace), @(sn_lineSpace), OBJC_ASSOCIATION_RETAIN);
}
- (CGFloat)sn_wordSpace
{
return [objc_getAssociatedObject(self, _cmd) floatValue];
}
- (void)setSn_wordSpace:(CGFloat)sn_wordSpace
{
objc_setAssociatedObject(self, @selector(sn_wordSpace), @(sn_wordSpace), OBJC_ASSOCIATION_RETAIN);
}
在load方法中我们通过 Swizze UIlabel的setText方法：
@implementation UILabel (SNExtension)
+ (void)load
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
SEL selectors[] = {
@selector(setText:),
};
for (NSUInteger index = 0; index < sizeof(selectors) / sizeof(SEL); ++index) {
SEL originalSelector = selectors[index];
SEL swizzledSelector = NSSelectorFromString([@"sn_" stringByAppendingString:NSStringFromSelector(originalSelector)]);
Method originalMethod = class_getInstanceMethod(self, originalSelector);
Method swizzledMethod = class_getInstanceMethod(self, swizzledSelector);
BOOL addedSuccess = class_addMethod(self, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
if (addedSuccess)
{
class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
}
else
{
method_exchangeImplementations(originalMethod, swizzledMethod);
}
}
});
}
- (void)sn_setText:(NSString *)text
{
[self sn_setText:text];
if (self.sn_lineSpace > 0)
{
NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithAttributedString:self.attributedText];
NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
paragraphStyle.lineSpacing = self.sn_lineSpace;
paragraphStyle.baseWritingDirection = NSWritingDirectionLeftToRight;
paragraphStyle.lineBreakMode = self.lineBreakMode;
paragraphStyle.alignment = self.textAlignment;
[attributedString addAttribute:NSParagraphStyleAttributeName value:paragraphStyle range:NSMakeRange(0, [self.text length])];
[attributedString addAttribute:NSFontAttributeName value:self.font range:NSMakeRange(0, [self.text length])];
self.attributedText = attributedString;
}
if (self.sn_wordSpace > 0 )
{
NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithAttributedString:self.attributedText];
[attributedString addAttribute:(__bridge NSString *)kCTKernAttributeName value:@(self.sn_wordSpace) range:NSMakeRange(0, [attributedString length])];
self.attributedText = attributedString;
}
}
貌似通过上面的代码就可以解决问题，我们在使用的时候，就可以
self.contentLabel.sn_lineSpace = 6.f;
但是这样会有一个问题，就是如果我们是先给Label复制然后在设置行间距是没有问题的，但是如果我们先给Label复制，然后在设置行间距，这个时候这个方法就不会生效。如何解决这个问题呢，我们需要做这样一个操作。我们需要同时swizze layoutSubviews方法,这样就可以了。
+ (void)load
{
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
SEL selectors[] = {
@selector(setText:),
@selector(layoutSubviews)
};
});
}
- (void)sn_layoutSubviews
{
[self sn_layoutSubviews];
if (self.sn_lineSpace > 0)
{
NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithAttributedString:self.attributedText];
NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
paragraphStyle.lineSpacing = self.sn_lineSpace;
paragraphStyle.baseWritingDirection = NSWritingDirectionLeftToRight;
// paragraphStyle.paragraphSpacing = 0.f;
paragraphStyle.lineBreakMode = self.lineBreakMode;
paragraphStyle.alignment = self.textAlignment;
[attributedString addAttribute:NSParagraphStyleAttributeName value:paragraphStyle range:NSMakeRange(0, [self.text length])];
[attributedString addAttribute:NSFontAttributeName value:self.font range:NSMakeRange(0, [self.text length])];
self.attributedText = attributedString;
}
if (self.sn_wordSpace > 0 )
{
NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithAttributedString:self.attributedText];
[attributedString addAttribute:(__bridge NSString *)kCTKernAttributeName value:@(self.sn_wordSpace) range:NSMakeRange(0, [attributedString length])];
self.attributedText = attributedString;
}
}