iOS Label實現文字漸變色效果

- (void)addGradientRampWithColors:(NSArray *)colors text:(NSString *)text {
 //label在父視圖上的（x，y）的值不是中心點
 CGPoint point = CGPointMake(30, 500);
 UILabel *label = [[UILabel alloc]init];
 label.text = text;
 label.font = [UIFont systemFontOfSize:20];
 // label.textAlignment = NSTextAlignmentCenter;
 [label sizeToFit];
 //label的中心和想象的一樣啦??！
 label.center = CGPointMake(point.x + CGRectGetWidth(label.bounds)/2, point.y - CGRectGetHeight(label.bounds)/2);
 [self.view addSubview:label];
 //這個label是和上面的label是對齊的哦，之前都不好對齊，用這樣的方法設置frame就好了
// UILabel *infoTextLabel = [[UILabel alloc] init];
// infoTextLabel.frame = CGRectMake(label.center.x - CGRectGetWidth(label.bounds)/2 ,point.y + 30, 220, 50);
// infoTextLabel.text = @"你說的是哦";
// infoTextLabel.font = [UIFont systemFontOfSize:20];
// infoTextLabel.backgroundColor =[UIColor redColor];
// infoTextLabel.numberOfLines = 0;
// infoTextLabel.textAlignment = NSTextAlignmentLeft;
// infoTextLabel.textColor = [UIColor blueColor];
// [infoTextLabel sizeToFit];
// [self.view addSubview:infoTextLabel];
 //在后面添加漸變圖層
 CAGradientLayer *gradientLayer = [CAGradientLayer layer];
 gradientLayer.frame = label.frame;
 gradientLayer.colors = colors;
 //漸變的方向（0，0） （0，1） （1，0）（1，1）為四個頂點方向
 //(I.e. [0,0] is the bottom-left
 // corner of the layer, [1,1] is the top-right corner.) The default values
 // are [.5,0] and [.5,1]
 gradientLayer.startPoint = CGPointMake(0, 1);
 gradientLayer.endPoint = CGPointMake(1, 1);
 [self.view.layer addSublayer:gradientLayer];
 gradientLayer.mask = label.layer;
 label.frame = gradientLayer.bounds;
}

@implementation CFGradientLabel

- (void)drawRect:(CGRect)rect {

 CGSize textSize = [self.text sizeWithAttributes:@{NSFontAttributeName : self.font}];
 CGRect textRect = (CGRect){0, 0, textSize};

 // 畫文字(不做顯示用, 主要作用是設置 layer 的 mask)
 CGContextRef context = UIGraphicsGetCurrentContext();
 [self.textColor set];
 [self.text drawWithRect:rect options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName : self.font} context:NULL];

 // 坐標(只對設置后的畫到 context 起作用, 之前畫的文字不起作用)
 CGContextTranslateCTM(context, 0.0f, rect.size.height - (rect.size.height - textSize.height) * 0.5);
 CGContextScaleCTM(context, 1.0f, -1.0f);

 CGImageRef alphaMask = CGBitmapContextCreateImage(context);
 CGContextClearRect(context, rect); // 清除之前畫的文字

 // 設置mask
 CGContextClipToMask(context, rect, alphaMask);

 // 畫漸變色
 CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
 CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef)self.colors, NULL);
 CGPoint startPoint = CGPointMake(textRect.origin.x,
          textRect.origin.y);
 CGPoint endPoint = CGPointMake(textRect.origin.x + textRect.size.width,
         textRect.origin.y + textRect.size.height);
 CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, kCGGradientDrawsBeforeStartLocation | kCGGradientDrawsAfterEndLocation);

 // 釋放內存
 CGColorSpaceRelease(colorSpace);
 CGGradientRelease(gradient);
 CFRelease(alphaMask);
}

@interface CFGradientLabel : UILabel

@property(nonatomic, strong) NSArray* colors;

@end

- (void)addGradientLabelWithFrame:(CGPoint)point gradientText:(NSString *)text infoText:(NSString *)infoText colors:(NSArray *)colors font:(UIFont *)font {

 static NSInteger labelTag = 200;
 CFGradientLabel *lable = [[CFGradientLabel alloc] init];
 lable.text = text;
 lable.font = font;
 lable.tag = labelTag;
 lable.textAlignment = NSTextAlignmentCenter;
 [lable sizeToFit];
 //之前項目的時候設置了為0，忘了注釋，所以有的小伙伴用的時候就不顯示了……(^-^)
// lable.alpha = 0;
 lable.center = point;
 lable.colors = colors;
 [self.view addSubview:lable];
}