iOS如何修改字體間距

iOS如何修改字體間距

iOS4及以下版本，並未提供直接修改字體間距的接口,字體間距都是系統默認大小。要DIY出不同字體間距的話，需要寫代碼實現。
使用Quartz 2D中的CGContextSetCharacterSpacing來實現修改字體間距。
Quartz 2D Programming Guide: Text
參考資料：
Is it possible to alter the letter-spacing/kerning of a font with Cocoa Touch?


例子代碼：


@interface RALabel : UILabel {
}
@end  

@implementation RALabel

- (void) drawRect:(CGRect)rect
{

    // Drawing code

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSelectFont (context, [self.font.fontName cStringUsingEncoding:NSASCIIStringEncoding], self.font.pointSize, kCGEncodingMacRoman);
    CGContextSetCharacterSpacing(context, 1);
    CGContextSetFillColorWithColor(context, [[UIColor clearColor] CGColor]);
    CGAffineTransform myTextTransform = CGAffineTransformScale(CGAffineTransformIdentity, 1.f, -1.f );
    CGContextSetTextMatrix (context, myTextTransform);

    // draw 1 but invisbly to get the string length.
    CGPoint p =CGContextGetTextPosition(context);
    float centeredY = (self.font.pointSize + (self.frame.size.height- self.font.pointSize)/2)-2;
    CGContextShowTextAtPoint(context, 0, centeredY, [self.text cStringUsingEncoding:NSASCIIStringEncoding], [self.text length]);
    CGPoint v =CGContextGetTextPosition(context);

    // calculate width and draw second one.
    float width = v.x - p.x;
    float centeredX =(self.frame.size.width- width)/2;
    CGContextSetFillColorWithColor(context, [self.textColor CGColor]);
    CGContextShowTextAtPoint(context, centeredX, centeredY, [self.text cStringUsingEncoding:NSASCIIStringEncoding], [self.text length]);

}