如何使用 NSString 绘制功能从文本创建 UIImage

Question

我想在 UIImage 中绘制 NSString 变量的内容，但我完全不知道如何做到这一点。我需要编写一个方法，该方法将接收 NSString 作为参数，并返回一个包含绘制到其中的文本的 UIImage 。

Answer 1

你可以试试这个：（针对 iOS 4 更新）

-(UIImage *)imageFromText:(NSString *)text
{
    // set the font type and size
    UIFont *font = [UIFont systemFontOfSize:20.0];  
    CGSize size  = [text sizeWithFont:font];

    // check if UIGraphicsBeginImageContextWithOptions is available (iOS is 4.0+)
    if (UIGraphicsBeginImageContextWithOptions != NULL)
        UIGraphicsBeginImageContextWithOptions(size,NO,0.0);
    else
        // iOS is < 4.0 
        UIGraphicsBeginImageContext(size);

    // optional: add a shadow, to avoid clipping the shadow you should make the context size bigger 
    //
    // CGContextRef ctx = UIGraphicsGetCurrentContext();
    // CGContextSetShadowWithColor(ctx, CGSizeMake(1.0, 1.0), 5.0, [[UIColor grayColor] CGColor]);

    // draw in context, you can use also drawInRect:withFont:
    [text drawAtPoint:CGPointMake(0.0, 0.0) withFont:font];

    // transfer image
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();    

    return image;
}

调用它：

UIImage *image = [self imageFromText:@"This is a text"];

Answer 2

添加 Swift 版本，还为您提供了更多选择：

class func sizeOfAttributeString(str: NSAttributedString, maxWidth: CGFloat) -> CGSize {
    let size = str.boundingRectWithSize(CGSizeMake(maxWidth, 1000), options:(NSStringDrawingOptions.UsesLineFragmentOrigin), context:nil).size
    return size
}

class func imageFromText(text:NSString, font:UIFont, maxWidth:CGFloat, color:UIColor) -> UIImage {
    let paragraph = NSMutableParagraphStyle()
    paragraph.lineBreakMode = NSLineBreakMode.ByWordWrapping
    paragraph.alignment = .Center // potentially this can be an input param too, but i guess in most use cases we want center align

    let attributedString = NSAttributedString(string: text, attributes: [NSFontAttributeName: font, NSForegroundColorAttributeName: color, NSParagraphStyleAttributeName:paragraph])

    let size = sizeOfAttributeString(attributedString, maxWidth: maxWidth)
    UIGraphicsBeginImageContextWithOptions(size, false , 0.0)
    attributedString.drawInRect(CGRectMake(0, 0, size.width, size.height))
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return image
}

Answer 3

使用 UIGraphicsBeginImageContext 开始图像上下文，绘制到它，使用 UIGraphicsGetImageFromCurrentImageContext 获取图像，使用 UIGraphicsEndImageContext 结束它

Answer 4

Swift 3.1

func sizeOfAttributeString(str: NSAttributedString, maxWidth: CGFloat) -> CGSize {
    let size = str.boundingRect(with: CGSize(width: maxWidth, height: 1000), options:(NSStringDrawingOptions.usesLineFragmentOrigin), context:nil).size
    return size
}

func imageFromText(text:NSString, font:UIFont, maxWidth:CGFloat, color:UIColor) -> UIImage {
    let paragraph = NSMutableParagraphStyle()
    paragraph.lineBreakMode = NSLineBreakMode.byWordWrapping
    paragraph.alignment = .center 

    let attributedString = NSAttributedString(string: text as String, attributes: [NSFontAttributeName: font, NSForegroundColorAttributeName: color, NSParagraphStyleAttributeName:paragraph])

    let size = sizeOfAttributeString(str: attributedString, maxWidth: maxWidth)
    UIGraphicsBeginImageContextWithOptions(size, false , 0.0)
    attributedString.draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return image!
}

感谢鲍蕾给出了漂亮的答案。