我想在我的属性字符串中添加一个 NSTextAttachment 图像，并使其垂直居中。
我使用以下代码创建了我的字符串：
NSMutableAttributedString *str = [[NSMutableAttributedString alloc] initWithString:DDLocalizedString(@"title.upcomingHotspots") attributes:attrs];
NSTextAttachment *attachment = [[NSTextAttachment alloc] init];
attachment.image = [[UIImage imageNamed:@"help.png"] imageScaledToFitSize:CGSizeMake(14.f, 14.f)];
cell.textLabel.attributedText = [str copy];
然而，该图片似乎与单元格的textLabel顶部对齐。
我该如何更改绘制附件的矩形区域？
你可以使用字体的capHeight属性。
Objective-C
NSTextAttachment *icon = [[NSTextAttachment alloc] init];
UIImage *iconImage = [UIImage imageNamed:@"icon.png"];
[icon setBounds:CGRectMake(0, roundf(titleFont.capHeight - iconImage.size.height)/2.f, iconImage.size.width, iconImage.size.height)];
[icon setImage:iconImage];
NSAttributedString *iconString = [NSAttributedString attributedStringWithAttachment:icon];
[titleText appendAttributedString:iconString];
Swift
let iconImage = UIImage(named: "icon.png")!
var icon = NSTextAttachment()
icon.bounds = CGRect(x: 0, y: (titleFont.capHeight - iconImage.size.height).rounded() / 2, width: iconImage.size.width, height: iconImage.size.height)
icon.image = iconImage
let iconString = NSAttributedString(attachment: icon)
titleText.append(iconString)
附件图像以文本基线为基础进行呈现。同时，它的y轴与核心绘图坐标系相反。如果您想将图像向上移动，请将bounds.origin.y设为正数。
图像应该与文本的capHeight垂直居中对齐。因此我们需要将bounds.origin.y设置为(capHeight - imageHeight)/2。
为了避免图像出现一些锯齿状的效果，我们应该在y的小数部分四舍五入。但是，字体和图像通常很小，即使只有1像素的差异，也会让图像看起来错位。因此，在除法之前，我使用了round函数。它使得y值的小数部分为.0或.5
在您的情况下，图像高度大于字体的capHeight。但是您仍然可以使用同样的方法。偏移量y值将为负值。并且它将从基线以下布局。
参考资料：
Apple developer iOS文本编程指南
尝试使用 - [NSTextAttachment bounds] 方法。不需要子类化。
为了上下文，我正在渲染一个 UILabel 以用作附件图像，然后设置边界框如下：
attachment.bounds = CGRectMake(0, self.font.descender, attachment.image.size.width, attachment.image.size.height) 这样标签图像中文字的基线与属性字符串行中的文本对齐。
attachment.bounds = CGRect(x: 0.0, y: self.font.descender, width: attachment.image!.size.width, height: attachment.image!.size.height) 的翻译如下：attachment.bounds 表示附件的边界，CGRect 是一个结构体，用来表示矩形区域。这段代码中，使用了四个参数来初始化 CGRect：x 表示左上角横坐标，y 表示左上角纵坐标，width 表示宽度，height 表示高度。其中，x 设为 0.0，y 设为 self.font.descender，即字体 descender 的值，attachment.image!.size.width 表示附件图片的宽度，attachment.image!.size.height 表示附件图片的高度。 - Andrewdescender属性！ - Benfunc textAttachment(fontSize: CGFloat) -> NSTextAttachment {
let font = UIFont.systemFontOfSize(fontSize) //set accordingly to your font, you might pass it in the function
let textAttachment = NSTextAttachment()
let image = //some image
textAttachment.image = image
let mid = font.descender + font.capHeight
textAttachment.bounds = CGRectIntegral(CGRect(x: 0, y: font.descender - image.size.height / 2 + mid + 2, width: image.size.width, height: image.size.height))
return textAttachment
}
应该能正常工作，并且不会有任何模糊的情况（感谢CGRectIntegral）
textAttachment.bounds = CGRect(x: 0, y: font.descender - image.size.height / 2 + mid + 2, width: image.size.height, height: image.size.height).integral - app4gNSTextAttachment 并重写 attachmentBoundsForTextContainer:proposedLineFragment:glyphPosition:characterIndex: 来改变矩形。 例如：- (CGRect)attachmentBoundsForTextContainer:(NSTextContainer *)textContainer proposedLineFragment:(CGRect)lineFrag glyphPosition:(CGPoint)position characterIndex:(NSUInteger)charIndex {
CGRect bounds;
bounds.origin = CGPointMake(0, -5);
bounds.size = self.image.size;
return bounds;
}
这并不是一个完美的解决方案。您必须“凭眼”找出Y轴原点，如果更改字体或图标大小，则可能需要更改Y轴原点。但我找不到更好的方法，除非将图标放在单独的图像视图中（这也有其缺点）。
怎么样：
CGFloat offsetY = -10.0;
NSTextAttachment *attachment = [NSTextAttachment new];
attachment.image = image;
attachment.bounds = CGRectMake(0.0,
offsetY,
attachment.image.size.width,
attachment.image.size.height);
无需子类化
@Travis提到的偏移量是字体下行高度。如果你还需要缩放图像，你需要使用NSTextAttachment的子类。以下是代码，灵感来自于这篇文章。我也将其发布在gist上。
import UIKit
class ImageAttachment: NSTextAttachment {
var verticalOffset: CGFloat = 0.0
// To vertically center the image, pass in the font descender as the vertical offset.
// We cannot get this info from the text container since it is sometimes nil when `attachmentBoundsForTextContainer`
// is called.
convenience init(_ image: UIImage, verticalOffset: CGFloat = 0.0) {
self.init()
self.image = image
self.verticalOffset = verticalOffset
}
override func attachmentBoundsForTextContainer(textContainer: NSTextContainer, proposedLineFragment lineFrag: CGRect, glyphPosition position: CGPoint, characterIndex charIndex: Int) -> CGRect {
let height = lineFrag.size.height
var scale: CGFloat = 1.0;
let imageSize = image!.size
if (height < imageSize.height) {
scale = height / imageSize.height
}
return CGRect(x: 0, y: verticalOffset, width: imageSize.width * scale, height: imageSize.height * scale)
}
}
使用方法如下:
var text = NSMutableAttributedString(string: "My Text")
let image = UIImage(named: "my-image")!
let imageAttachment = ImageAttachment(image, verticalOffset: myLabel.font.descender)
text.appendAttributedString(NSAttributedString(attachment: imageAttachment))
myLabel.attributedText = text
extension NSTextAttachment {
static func getCenteredImageAttachment(with imageName: String, and
font: UIFont?) -> NSTextAttachment? {
let imageAttachment = NSTextAttachment()
guard let image = UIImage(named: imageName),
let font = font else { return nil }
imageAttachment.bounds = CGRect(x: 0, y: (font.capHeight - image.size.height).rounded() / 2, width: image.size.width, height: image.size.height)
imageAttachment.image = image
return imageAttachment
}
}
然后您可以发送图像名称和字体进行呼叫：
let imageAttachment = NSTextAttachment.getCenteredImageAttachment(with: imageName,
and: youLabel?.font)
然后将imageAttachment追加到attributedString中
如果您有一个非常大的上升高度，并且想像我一样将图片居中（在小写字母盖高度的中心位置），请尝试以下方法
let attachment: NSTextAttachment = NSTextAttachment()
attachment.image = image
if let image = attachment.image{
let y = -(font.ascender-font.capHeight/2-image.size.height/2)
attachment.bounds = CGRect(x: 0, y: y, width: image.size.width, height: image.size.height).integral
}
y的计算如下图所示
请注意，y值为0，因为我们希望图像从原点向下移动
如果您希望它位于整个标签的中间，请使用此y值：
let y = -((font.ascender-font.descender)/2-image.size.height/2)
func updateUI(text: String?) {
guard let text = text else {
attributedText = nil
return
}
let attributedString = NSMutableAttributedString(string:"")
let textAttachment = NSTextAttachment ()
textAttachment.image = image
let sizeSide: CGFloat = 8
let iconsSize = CGRect(x: CGFloat(0),
y: (font.capHeight - sizeSide) / 2,
width: sizeSide,
height: sizeSide)
textAttachment.bounds = iconsSize
attributedString.append(NSAttributedString(attachment: textAttachment))
attributedString.append(NSMutableAttributedString(string: text))
attributedText = attributedString
sizeToFit()
}
可以使用NSAttributedString.Key.baselineOffset属性来在NSMutbleAttributedString中垂直移动NSTextAttachment。