Ios 如何为UITextField实现类似NSLineBreakbyTruncingHead的功能？

我需要为

UITextField

实现类似于

NSLineBreakByTruncatingHead

的功能，如下所示。假设原文是：

这是无法在UITextField中显示的长文本

我需要它，就像：

…无法显示在UITextField内

但目前我得到的是：

这是一篇很长的文章，不能

只需在开始时进行截断。未为

UITextField

提供

lineBreakMode

属性。如何实现它？

我采用了解决方案，并对其进行了修改，以截断字符串的头部而不是尾部。请知道，它仅在未编辑字段时显示省略号

注意：此解决方案仅适用于iOS 7+版本。要在iOS 6中使用，请在NSString+truncateTowitWidth.m文件中使用

sizeWidthFont:

而不是

sizeWidthAttributes:

。
编辑：增加了对iOS 6的支持

NSString+TruncateToWidth.h

@interface NSString (TruncateToWidth)
- (NSString*)stringByTruncatingToWidth:(CGFloat)width withFont:(UIFont *)font;
@end

NSString+TruncateToWidth.m

#import "NSString+TruncateToWidth.h"

#define ellipsis @"…"

@implementation NSString (TruncateToWidth)

- (NSString*)stringByTruncatingToWidth:(CGFloat)width withFont:(UIFont *)font
{
    // Create copy that will be the returned result
    NSMutableString *truncatedString = [self mutableCopy];

    // Make sure string is longer than requested width
    if ([self widthWithFont:font] > width)
    {
        // Accommodate for ellipsis we'll tack on the beginning
        width -= [ellipsis widthWithFont:font];

        // Get range for first character in string
        NSRange range = {0, 1};

        // Loop, deleting characters until string fits within width
        while ([truncatedString widthWithFont:font] > width)
        {
            // Delete character at beginning
            [truncatedString deleteCharactersInRange:range];
        }

        // Append ellipsis
        [truncatedString replaceCharactersInRange:NSMakeRange(0, 0) withString:ellipsis];
    }

    return truncatedString;
}

- (CGFloat)widthWithFont:(UIFont *)font
{
    if([self respondsToSelector:@selector(sizeWithAttributes:)])
        return [self sizeWithAttributes:@{NSFontAttributeName:font}].width;
    return [self sizeWithFont:font].width;
}

使用它：

...
// Make sure to import the header file where you want to use it
// assumes instance variable holds your string that populates the field
fieldString = @"abcdefghijklmnopqrstuvwxyz1234567890";
// Size will need to be less than text field's width to account for padding
_myTextField.text = [fieldString stringByTruncatingToWidth:(_myTextField.frame.size.width - 15) withFont:_myTextField.font];
...

// use textFieldShouldBeginEditing to make it animate from the start of the field to the end of the string if you prefer that. I found it a little distracting
- (void)textFieldDidBeginEditing:(UITextField *)textField
{
    textField.text = fieldString;
}

- (BOOL)textFieldShouldEndEditing:(UITextField *)textField
{
    fieldString = textField.text;
    textField.text = [textField.text stringByTruncatingToWidth:(textField.frame.size.width - 15) withFont:textField.font];

    return YES;
}

---

我有一个类似的要求，我写了一个@Stonz2解决方案的Swift版本，它在大多数情况下都有效，但由于该要求后来被删除，尚未在生产中使用。。。无论如何，把它贴在这里

    extension String {

    func stringByTruncatingLeadingForWidth(width: CGFloat, withFont font: UIFont) -> String{

        var modifiedString = self
        var mutableWidth = width
        let ellipsis = "..."
        if (self.widthOfString(usingFont: font) > width) {
            let ellipsisWidth = ellipsis.widthOfString(usingFont: font)

            // else this will go for infinite loop...mutable width will go -ve
            if mutableWidth > ellipsisWidth {
                mutableWidth -= ellipsis.widthOfString(usingFont: font)
            }
            let range = NSMakeRange(0, 1)

            while modifiedString.widthOfString(usingFont: font) > mutableWidth {
                modifiedString.deleteCharactersInRange(range: range)
                print(modifiedString)
                print(mutableWidth)
            }
            guard let swiftRange = Range(NSMakeRange(0, 3), in: modifiedString) else { return ""  }
            modifiedString.replaceSubrange(swiftRange, with: [".",".","."])
        }
        return modifiedString
    }
    func widthOfString(usingFont font: UIFont) -> CGFloat {
        let fontAttributes = [NSAttributedString.Key.font: font]
        let size = self.size(withAttributes: fontAttributes)
        return size.width
    }

    mutating func deleteCharactersInRange(range: NSRange) {
        guard let swiftRange = Range(range, in: self) else { return  }
        self.removeSubrange(swiftRange)
    }
}

var str1 = "Hello how are you"

let newStr = str1.stringByTruncatingLeadingForWidth(width: 100, withFont: .systemFont(ofSize: 15))

---

我不得不把“padding”的数字比预期的（15）高一点，因为它有时不够短，并且会在末尾加上一个省略号。谢谢你，我已经投票了，因为你真的找到了它，而且你的解释很清楚。再次感谢，从苹果的文档来看，这非常简单。