如何将后续文本添加到uitextfield [英] How to add followed text to uitextfield

问题描述

我有一个带有占位符的文本字段，名为 letschat 。现在每当我开始输入我的文本字段时，我想将我的文本字段显示为某些@letschat 。当我的文本字段为空时，我的占位符必须显示。我做了。但是每当我开始在文本字段中输入时，我想设置。无论我输入什么，我希望这个文本也可见：

I have one text field with place holder called letschat. Now whenever I start typing in my textfield, I want to show my textfield as some @letschat. When my textfield is empty that time my placeholder have to show. That I did. But I want to set whenever I start typing in my textfield. Whatever I am typing with that I want this text also to visible like:

一些@Lletchat

Some @Lletschat

我该怎么做？

推荐答案

我创建了 UITextField 使用占位符（如果设置）作为后缀的子类。据我所知，一切都按预期工作。也许需要进行一些调整以满足您的需求。

I created a UITextField subclass that uses the placeholder (if set) as a suffix. As far as I can see everything works as expected. Maybe there are some tweaks needed to suit your needs.

随意询问是否有任何不清楚的地方：

Feel free to ask if anything is unclear:

class SuffixTextField: UITextField {

    override init(frame: CGRect) {
        super.init(frame: frame)
        sharedInit()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        sharedInit()
    }

    private func sharedInit() {
        addTarget(self, action: #selector(textChanged), for: .editingChanged)
    }

    override var text: String? {
        didSet {
            selectedTextRange = maxTextRange
        }
    }

    override var attributedText: NSAttributedString? {
        didSet {
            selectedTextRange = maxTextRange
        }
    }

    @objc private func textChanged() {
        if let currentText = text, let placeholder = placeholder {
            if currentText == placeholder {
                self.text = nil
            } else if !currentText.hasSuffix(placeholder) {
                self.text = currentText + placeholder
            }
        }
    }

    private var maxCursorPosition: UITextPosition? {
        guard let placeholder = placeholder, !placeholder.isEmpty else { return nil }
        guard let text = text, !text.isEmpty else { return nil }
        return position(from: beginningOfDocument, offset: (text as NSString).range(of: placeholder, options: .backwards).location)
    }

    private var maxTextRange: UITextRange? {
        guard let maxCursorPosition = maxCursorPosition else { return nil }
        return textRange(from: maxCursorPosition, to: maxCursorPosition)
    }

    override var selectedTextRange: UITextRange? {
        get { return super.selectedTextRange }
        set {
            guard let newRange = newValue,
                let maxCursorPosition = maxCursorPosition else {
                    super.selectedTextRange = newValue
                    return
            }

            if compare(maxCursorPosition, to: newRange.start) == .orderedAscending {
                super.selectedTextRange = textRange(from: maxCursorPosition, to: maxCursorPosition)
            } else if compare(maxCursorPosition, to: newRange.end) == .orderedAscending {
                super.selectedTextRange = textRange(from: newRange.start, to: maxCursorPosition)
            } else {
                super.selectedTextRange = newValue
            }
        }
    }

}

在这里你可以看到预览：
https://www.dropbox.com/s/etkbme37wuxbw1q/preview.mov?dl=0

here you can see a preview: https://www.dropbox.com/s/etkbme37wuxbw1q/preview.mov?dl=0

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