在单行 UILabel 旁边居中 NSTextAttachment 图像

Question

我想将NSTextAttachment 图像附加到我的属性字符串并使其垂直居中。

我使用以下代码来创建我的字符串：

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];

但是，图像似乎与单元格顶部的 textLabel 对齐。

如何更改绘制附件的矩形？

Answer 1

您可以使用字体的 capHeight。

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];

斯威夫特

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)

附件图像呈现在文本的基线上。 并且它的y轴像核心图形坐标系一样反转。 如果要向上移动图像，请将bounds.origin.y 设置为正值。

图像应与文本的 capHeight 垂直居中对齐。 所以我们需要将bounds.origin.y设置为(capHeight - imageHeight)/2。

为了避免对图像产生一些锯齿状的影响，我们应该对 y 的小数部分进行四舍五入。但是字体和图像通常很小，即使是 1px 的差异也会使图像看起来像未对齐。所以我在划分之前应用了round函数。它将 y 值的小数部分设为 .0 或 .5

在您的情况下，图像高度大于字体的 capHeight。但是你可以用同样的方法。偏移 y 值将为负数。并且会从基线的下方开始布局。

Answer 2

试试- [NSTextAttachment bounds]。不需要子类化。

对于上下文，我正在渲染一个UILabel 用作附件图像，然后像这样设置边界： attachment.bounds = CGRectMake(0, self.font.descender, attachment.image.size.width, attachment.image.size.height) 和标签图像中的文本基线和属性字符串中的文本根据需要排列。

Answer 3

您可以通过继承NSTextAttachment 并覆盖attachmentBoundsForTextContainer:proposedLineFragment:glyphPosition:characterIndex: 来更改矩形。示例：

- (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;
}

这不是一个完美的解决方案。您必须“通过眼睛”找出 Y 原点，如果您更改字体或图标大小，您可能需要更改 Y 原点。但是我找不到更好的方法，除了将图标放在单独的图像视图中（这有其自身的缺点）。

Answer 4

我找到了一个完美的解决方案，虽然对我来说就像一个魅力，但是你必须自己尝试一下（可能常数取决于设备的分辨率，也可能是其他因素；）

func 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
}

应该有效并且不应该以任何方式模糊（感谢CGRectIntegral）

Answer 5

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);

不需要子类化

Answer 6

@Travis 是正确的，偏移量是字体下降器。如果还需要缩放图像，则需要使用 NSTextAttachment 的子类。下面是受this article启发的代码。我还将其发布为gist。

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)
    }
}

如下使用：

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

Answer 7

如果你有一个非常大的上升点并且想像我一样将图像居中（大写高度的中心）试试这个

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计算如下图

注意y值为0，因为我们希望图像从原点向下移动

如果你想让它在整个标签的中间。使用这个 y 值：

let y = -((font.ascender-font.descender)/2-image.size.height/2)

Answer 8

我们可以在 swift 4 中做一个扩展，生成一个带有像这样居中图像的附件：

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
    }
}

然后您可以拨打电话发送图像的名称和字体：

let imageAttachment = NSTextAttachment.getCenteredImageAttachment(with: imageName,
                                                                   and: youLabel?.font)

然后将 imageAttachment 附加到属性字符串

Answer 9

就我而言，调用 sizeToFit() 会有所帮助。 在 Swift 5.1 中

在您的自定义标签内：

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()
}

Answer 10

请使用 -lineFrag.size.height/5.0 作为边界高度。这使图像完全居中并与所有字体大小的文本对齐

override func attachmentBoundsForTextContainer(textContainer: NSTextContainer, proposedLineFragment lineFrag: CGRect, glyphPosition position: CGPoint, characterIndex charIndex: Int) -> CGRect
{
    var bounds:CGRect = CGRectZero

    bounds.size = self.image?.size as CGSize!
    bounds.origin = CGPointMake(0, -lineFrag.size.height/5.0);

    return bounds;
}