在文本字段中居中对齐占位符

Question

我知道这个问题被问过很多次，但由于不推荐使用 drawinrect，我在 ios 8 中需要这个。因为我有一个文本字段，我需要居中对齐的占位符，其余的测试左对齐。请帮帮我。

Answer 1

您可以使用带有对齐设置为.center 的段落样式的attributedPlaceholder 来居中占位符：

let centeredParagraphStyle = NSMutableParagraphStyle()
centeredParagraphStyle.alignment = .center
textField.attributedPlaceholder = NSAttributedString(
    string: "Placeholder", 
    attributes: [.paragraphStyle: centeredParagraphStyle]
)

Answer 2

创建 IBOutlet 并将其连接到您的文本字段。在 YourViewController.m

@interface YourViewController () <UITextFieldDelegate>
@property (weak, nonatomic) IBOutlet UITextField *txt;

在您的 viewDidLoad

中

self.txt.delegate=self;
self.txt.textAlignment=NSTextAlignmentCenter;

编写此委托方法。每次文本字段中的文本更改时都会调用此方法。

- (BOOL) textField: (UITextField *)theTextField shouldChangeCharactersInRange: (NSRange)range replacementString: (NSString *)string {

    NSRange textFieldRange = NSMakeRange(0, [self.txt.text length]);
    // Check If textField is empty. If empty align your text field to center, so that placeholder text will show center aligned
    if (NSEqualRanges(range, textFieldRange) && [string length] == 0) {
    self.txt.textAlignment=NSTextAlignmentCenter;
    }
    else //else align textfield to left. 
    {
        self.txt.textAlignment=NSTextAlignmentLeft;
    }
    return YES;
}

Answer 3

@Clay Ellis 的答案是正确的，这是针对 Objective-C 的：

UITextField* field = [[UITextField alloc] initWithFrame: fieldRect];
NSTextAlignment alignment = NSTextAlignmentCenter;
NSMutableParagraphStyle* alignmentSetting = [[NSMutableParagraphStyle alloc] init];
alignmentSetting.alignment = alignment;
NSDictionary *attributes = @{NSParagraphStyleAttributeName : alignmentSetting};
NSAttributedString *str = [[NSAttributedString alloc] initWithString:placeholder attributes: attributes];
field.attributedPlaceholder = str;

Answer 4

基于克莱·埃利斯的回答

详情

• Xcode 版本 10.2.1 (10E1001)，Swift 5

解决方案 1

let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.alignment = .center
textField.attributedText = NSAttributedString(string: placeholder, attributes: [.paragraphStyle: paragraphStyle])

解决方案 2

import Foundation

extension String {
    func toAttributed(alignment: NSTextAlignment) -> NSAttributedString {
        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.alignment = .center
        return toAttributed(attributes: [.paragraphStyle: paragraphStyle])
    }

    func toAttributed(attributes: [NSAttributedString.Key : Any]? = nil) -> NSAttributedString {
        return NSAttributedString(string: self, attributes: attributes)
    }
}

解决方案2的使用

// Way 1
textField.attributedPlaceholder = text.attributedString(alignment: .center)
// Way 2
textField.attributedPlaceholder = "title".attributedString(alignment: .center)

完整样本

别忘了在此处添加解决方案代码

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        let textField = UITextField()
        textField.borderStyle = .roundedRect
        view.addSubview(textField)
        //textField.attributedPlaceholder = getAttributedString1()
        textField.attributedPlaceholder = getAttributedString2()
        textField.translatesAutoresizingMaskIntoConstraints = false
        textField.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 24).isActive = true
        textField.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor, constant: 16).isActive = true
        view.safeAreaLayoutGuide.rightAnchor.constraint(equalTo: textField.rightAnchor, constant: 16).isActive = true
    }

    private func getAttributedString1() -> NSAttributedString {
        return "placeholder".toAttributed(alignment: .center)
    }

    private func getAttributedString2() -> NSAttributedString {
        var attributes = [NSAttributedString.Key: Any]()
        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.alignment = .center
        attributes[.paragraphStyle] = paragraphStyle
        attributes[.font] = UIFont.systemFont(ofSize: 12, weight: .bold)
        attributes[.foregroundColor] = UIColor.black.withAlphaComponent(0.5)
        attributes[.underlineStyle] = NSUnderlineStyle.single.rawValue
        attributes[.underlineColor] = UIColor.red
        return "placeholder".toAttributed(attributes: attributes)
    }
}

结果

Answer 5

@Clay Ellis 在 Swift 5 中的回答

let centeredParagraphStyle = NSMutableParagraphStyle()
    centeredParagraphStyle.alignment = .center
    let attributedPlaceholder = NSAttributedString(string: "Placeholder", attributes: [NSAttributedString.Key.paragraphStyle: centeredParagraphStyle])
    textField.attributedPlaceholder = attributedPlaceholder