使用

[@"I‘m 六弦琴殇" animateOnView:self.view atRect:CGRectMake(120, 20, 200, 200) forFont:[UIFont systemFontOfSize:30] withColor:[UIColor redColor] andDuration:8.0];

源码
UIBezierPath (TextPath)

@interface UIBezierPath (TextPath)
+ (UIBezierPath *)bezierPathWithText:(NSString *)text font:(UIFont *)font;
@end

@implementation UIBezierPath (TextPath)

+ (UIBezierPath *)bezierPathWithText:(NSString *)text font:(UIFont *)font {
    CTFontRef ctFont = CTFontCreateWithName((__bridge CFStringRef)font.fontName, font.pointSize, NULL);
    if (!ctFont) return nil;
    NSDictionary *attrs = @{ (__bridge id)kCTFontAttributeName:(__bridge id)ctFont };
    NSAttributedString *attrString = [[NSAttributedString alloc] initWithString:text attributes:attrs];
    CFRelease(ctFont);
    
    CTLineRef line = CTLineCreateWithAttributedString((__bridge CFTypeRef)attrString);
    if (!line) return nil;
    
    CGMutablePathRef cgPath = CGPathCreateMutable();
    CFArrayRef runs = CTLineGetGlyphRuns(line);
    for (CFIndex iRun = 0, iRunMax = CFArrayGetCount(runs); iRun < iRunMax; iRun++) {
        CTRunRef run = (CTRunRef)CFArrayGetValueAtIndex(runs, iRun);
        CTFontRef runFont = CFDictionaryGetValue(CTRunGetAttributes(run), kCTFontAttributeName);
        
        for (CFIndex iGlyph = 0, iGlyphMax = CTRunGetGlyphCount(run); iGlyph < iGlyphMax; iGlyph++) {
            CFRange glyphRange = CFRangeMake(iGlyph, 1);
            CGGlyph glyph;
            CGPoint position;
            CTRunGetGlyphs(run, glyphRange, &glyph);
            CTRunGetPositions(run, glyphRange, &position);
            
            CGPathRef glyphPath = CTFontCreatePathForGlyph(runFont, glyph, NULL);
            if (glyphPath) {
                CGAffineTransform transform = CGAffineTransformMakeTranslation(position.x, position.y);
                CGPathAddPath(cgPath, &transform, glyphPath);
                CGPathRelease(glyphPath);
            }
        }
    }
    UIBezierPath *path = [UIBezierPath bezierPathWithCGPath:cgPath];
    CGRect boundingBox = CGPathGetPathBoundingBox(cgPath);
    CFRelease(cgPath);
    CFRelease(line);
    
    [path applyTransform:CGAffineTransformMakeScale(1.0, -1.0)];
    [path applyTransform:CGAffineTransformMakeTranslation(0.0, boundingBox.size.height)];
    
    return path;
}

@end

NSString(Animation)

@interface NSString(Animation)
- (void)animateOnView:(UIView *)aView atRect:(CGRect)aRect forFont:(UIFont *)aFont withColor:(UIColor *)aColor andDuration:(CGFloat)aDuration;
@end

@implementation NSString(Animation)
- (void)animateOnView:(UIView *)aView atRect:(CGRect)aRect forFont:(UIFont *)aFont withColor:(UIColor *)aColor andDuration:(CGFloat)aDuration
{
    // 创建文字路径
    UIBezierPath *path = [UIBezierPath bezierPathWithText:self font:aFont];
    
    // 创建路径图层
    CAShapeLayer *pathLayer = [CAShapeLayer layer];
    pathLayer.frame = aRect;
    pathLayer.bounds = CGPathGetBoundingBox(path.CGPath);
    pathLayer.geometryFlipped = NO;
    pathLayer.path = path.CGPath;
    pathLayer.strokeColor = [aColor CGColor];
    pathLayer.fillColor = nil;
    pathLayer.lineWidth = 1.0f;
    pathLayer.lineJoin = kCALineJoinBevel;
    [aView.layer addSublayer:pathLayer];
    
    // 创建画笔图层
    UIImage *penImage = [UIImage imageNamed:@"pencil.png"];
    CALayer *penLayer = [CALayer layer];
    penLayer.contents = (id)penImage.CGImage;
    penLayer.anchorPoint = CGPointMake(0, 1);
    penLayer.frame = CGRectMake(0.0f, 0.0f, penImage.size.width, penImage.size.height);
    [pathLayer addSublayer:penLayer];
   
    // 绘图动画
    CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];// strokeStart 是擦除效果
    pathAnimation.duration = aDuration;
    pathAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
    pathAnimation.toValue = [NSNumber numberWithFloat:1.0f];
    pathAnimation.removedOnCompletion = YES;

    [pathLayer addAnimation:pathAnimation forKey:@"strokeEnd"];
    // 画笔动画
    CAKeyframeAnimation *penAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    penAnimation.duration = aDuration;
    penAnimation.path = path.CGPath;
    penAnimation.calculationMode = kCAAnimationPaced;
    penAnimation.removedOnCompletion = YES;
    [penLayer addAnimation:penAnimation forKey:@"position"];
}

@end