ios - 如何在 Swift 中从自定义文本生成 UIImage

Question

我正在尝试从 Swift3 中的自定义文本生成一个 UIImage。

使用 iOS 控件，可以创建一个 UIImage，下面是代码:

class func imageWithText(txtField: UITextField) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(txtField.bounds.size, false, 0.0)
        txtField.layer.render(in: UIGraphicsGetCurrentContext()!)
        let img = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return img!
    }

注意:我知道也可以在图像中添加一些文本，但我不想这样做。

有人可以帮我解决这个问题吗？谢谢!

Answer 1

这是一个 String 扩展，可以如下所示用于从 String 实例创建 UIImage 实例，没有需要像 UITextField 或 UILabel 这样的 UI 控件:

var image: UIImage? =
    "Test".image(withAttributes: [
        .foregroundColor: UIColor.red,
        .font: UIFont.systemFont(ofSize: 30.0),
    ], size: CGSize(width: 300.0, height: 80.0))

// Or
image = "Test".image(withAttributes: [.font: UIFont.systemFont(ofSize: 80.0)])

// Or
image = "Test".image(size: CGSize(width: 300.0, height: 80.0))

// Or even just
image = "Test".image()

以下是实现上述预期效果的两种可能的实现方式:

UIGraphicsImageRenderer 方法(性能更高，Apple 推荐实现)

extension String {
    
    /// Generates a `UIImage` instance from this string using a specified
    /// attributes and size.
    ///
    /// - Parameters:
    ///     - attributes: to draw this string with. Default is `nil`.
    ///     - size: of the image to return.
    /// - Returns: a `UIImage` instance from this string using a specified
    /// attributes and size, or `nil` if the operation fails.
    func image(withAttributes attributes: [NSAttributedString.Key: Any]? = nil, size: CGSize? = nil) -> UIImage? {
        let size = size ?? (self as NSString).size(withAttributes: attributes)
        return UIGraphicsImageRenderer(size: size).image { _ in
            (self as NSString).draw(in: CGRect(origin: .zero, size: size),
                                    withAttributes: attributes)
        }
    }
    
}

UIGraphicsImageContext 方法(老派；包括在内是为了彻底)

extension String {
    
    /// Generates a `UIImage` instance from this string using a specified
    /// attributes and size.
    ///
    /// - Parameters:
    ///     - attributes: to draw this string with. Default is `nil`.
    ///     - size: of the image to return.
    /// - Returns: a `UIImage` instance from this string using a specified
    /// attributes and size, or `nil` if the operation fails.
    func image(withAttributes attributes: [NSAttributedString.Key: Any]? = nil, size: CGSize? = nil) -> UIImage? {
        let size = size ?? (self as NSString).size(withAttributes: attributes)
        UIGraphicsBeginImageContext(size)
        (self as NSString).draw(in: CGRect(origin: .zero, size: size), 
                                withAttributes: attributes)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }
    
}