如何在UITextView中添加占位符,类似于你可以为UITextField设置的占位符,在Swift中?
当前回答
有我的简单版本的UITextView与占位符。主要思想是:
隐藏占位符,如果用户开始编辑和占位符是可见的 如果用户结束编辑并且文本视图的文本为空,则显示占位符。
class PlaceholderTextView: UITextView {
var placeholder = "" {
didSet {
if isPlaceholderVisible {
showPlaceholder()
}
}
}
var isPlaceholderVisible = true {
didSet {
isPlaceholderVisible ? showPlaceholder() : hidePlaceholder()
}
}
init() {
super.init(frame: .zero, textContainer: nil)
delegate = self
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
private func showPlaceholder() {
text = placeholder
// Set other things like color of text for placeholder, ...
}
private func hidePlaceholder() {
text = ""
// Set other things like color of text for normal input, ...
}
}
extension PlaceholderTextView: UITextViewDelegate {
func textViewDidBeginEditing(_ textView: UITextView) {
if isPlaceholderVisible {
isPlaceholderVisible = false
}
}
func textViewDidEndEditing(_ textView: UITextView) {
if text.isEmpty {
isPlaceholderVisible = true
}
}
}
其他回答
基于这里已经给出的一些很好的建议,我能够将以下轻量级的、与接口生成器兼容的UITextView子类组合在一起,它是:
包括可配置的占位符文本,样式就像UITextField一样。 不需要任何额外的子视图或约束。 不需要来自ViewController的任何委托或其他行为。 不需要任何通知。 保持占位符文本与查看字段文本属性的任何外部类完全分离。
任何改进建议都是受欢迎的,特别是如果有任何方法通过编程来获取iOS的占位符颜色,而不是硬编码它。
斯威夫特v5:
import UIKit
@IBDesignable class TextViewWithPlaceholder: UITextView {
override var text: String! { // Ensures that the placeholder text is never returned as the field's text
get {
if showingPlaceholder {
return "" // When showing the placeholder, there's no real text to return
} else { return super.text }
}
set { super.text = newValue }
}
@IBInspectable var placeholderText: String = ""
@IBInspectable var placeholderTextColor: UIColor = UIColor(red: 0.78, green: 0.78, blue: 0.80, alpha: 1.0) // Standard iOS placeholder color (#C7C7CD). See https://stackoverflow.com/questions/31057746/whats-the-default-color-for-placeholder-text-in-uitextfield
private var showingPlaceholder: Bool = true // Keeps track of whether the field is currently showing a placeholder
override func didMoveToWindow() {
super.didMoveToWindow()
if text.isEmpty {
showPlaceholderText() // Load up the placeholder text when first appearing, but not if coming back to a view where text was already entered
}
}
override func becomeFirstResponder() -> Bool {
// If the current text is the placeholder, remove it
if showingPlaceholder {
text = nil
textColor = nil // Put the text back to the default, unmodified color
showingPlaceholder = false
}
return super.becomeFirstResponder()
}
override func resignFirstResponder() -> Bool {
// If there's no text, put the placeholder back
if text.isEmpty {
showPlaceholderText()
}
return super.resignFirstResponder()
}
private func showPlaceholderText() {
showingPlaceholder = true
textColor = placeholderTextColor
text = placeholderText
}
}
斯威夫特5.2
独立的类
如果你想要一个类,你可以在任何地方使用,因为它是自包含的
import UIKit
class PlaceHolderTextView:UITextView, UITextViewDelegate{
var placeholderText = "placeholderText"
override func willMove(toSuperview newSuperview: UIView?) {
textColor = .lightText
delegate = self
}
func textViewDidBeginEditing(_ textView: UITextView) {
if textView.text == placeholderText{
placeholderText = textView.text
textView.text = ""
textView.textColor = .darkText
}
}
func textViewDidEndEditing(_ textView: UITextView) {
if textView.text == ""{
textView.text = placeholderText
textColor = .lightText
}
}
}
这里的关键是willMove(toSuperView:)函数,因为它允许你在添加到另一个视图的层次结构之前设置视图(类似于ViewControllers中的viewDidLoad/viewWillAppear)
我很惊讶没有人提到NSTextStorageDelegate。UITextViewDelegate的方法只能由用户交互触发,而不是以编程方式触发。例如,当你以编程方式设置一个文本视图的文本属性时,你必须自己设置占位符的可见性,因为委派方法不会被调用。
然而,使用NSTextStorageDelegate的textStorage(_:didProcessEditing:range:changeInLength:)方法,你会收到任何文本更改的通知,即使它是通过编程完成的。就像这样分配它:
textView.textStorage.delegate = self
(在UITextView中,这个委派属性默认为nil,所以它不会影响任何默认行为。)
将它与@clearlight演示的UILabel技术结合起来,可以轻松地将整个UITextView的占位符实现包装成一个扩展。
extension UITextView {
private class PlaceholderLabel: UILabel { }
private var placeholderLabel: PlaceholderLabel {
if let label = subviews.compactMap( { $0 as? PlaceholderLabel }).first {
return label
} else {
let label = PlaceholderLabel(frame: .zero)
label.font = font
addSubview(label)
return label
}
}
@IBInspectable
var placeholder: String {
get {
return subviews.compactMap( { $0 as? PlaceholderLabel }).first?.text ?? ""
}
set {
let placeholderLabel = self.placeholderLabel
placeholderLabel.text = newValue
placeholderLabel.numberOfLines = 0
let width = frame.width - textContainer.lineFragmentPadding * 2
let size = placeholderLabel.sizeThatFits(CGSize(width: width, height: .greatestFiniteMagnitude))
placeholderLabel.frame.size.height = size.height
placeholderLabel.frame.size.width = width
placeholderLabel.frame.origin = CGPoint(x: textContainer.lineFragmentPadding, y: textContainerInset.top)
textStorage.delegate = self
}
}
}
extension UITextView: NSTextStorageDelegate {
public func textStorage(_ textStorage: NSTextStorage, didProcessEditing editedMask: NSTextStorageEditActions, range editedRange: NSRange, changeInLength delta: Int) {
if editedMask.contains(.editedCharacters) {
placeholderLabel.isHidden = !text.isEmpty
}
}
}
注意,使用了一个名为PlaceholderLabel的私有(嵌套)类。它根本没有实现,但它为我们提供了一种识别占位符标签的方法,这比使用tag属性要“快捷”得多。
使用这种方法,你仍然可以将UITextView的委托分配给其他人。
你甚至不需要改变文本视图的类。只要添加扩展,你就可以为项目中的每个UITextView分配一个占位符字符串,甚至在接口生成器中也是如此。
出于清晰的原因,我省略了placeholderColor属性的实现,但是它可以用与placeholder类似的计算变量在多几行中实现。
这是我准备使用的解决方案,如果您正在处理多个文本视图
func textViewShouldBeginEditing(textView: UITextView) -> Bool {
// Set cursor to the beginning if placeholder is set
if textView.textColor == UIColor.lightGrayColor() {
textView.selectedTextRange = textView.textRangeFromPosition(textView.beginningOfDocument, toPosition: textView.beginningOfDocument)
}
return true
}
func textView(textView: UITextView, shouldChangeTextInRange range: NSRange, replacementText text: String) -> Bool {
// Remove placeholder
if textView.textColor == UIColor.lightGrayColor() && text.characters.count > 0 {
textView.text = ""
textView.textColor = UIColor.blackColor()
}
if text == "\n" {
textView.resignFirstResponder()
return false
}
return true
}
func textViewDidChange(textView: UITextView) {
// Set placeholder if text is empty
if textView.text.isEmpty {
textView.text = NSLocalizedString("Hint", comment: "hint")
textView.textColor = UIColor.lightGrayColor()
textView.selectedTextRange = textView.textRangeFromPosition(textView.beginningOfDocument, toPosition: textView.beginningOfDocument)
}
}
func textViewDidChangeSelection(textView: UITextView) {
// Set cursor to the beginning if placeholder is set
let firstPosition = textView.textRangeFromPosition(textView.beginningOfDocument, toPosition: textView.beginningOfDocument)
// Do not change position recursively
if textView.textColor == UIColor.lightGrayColor() && textView.selectedTextRange != firstPosition {
textView.selectedTextRange = firstPosition
}
}
func setPlaceholder(){ var placeholderLabel = UILabel() placeholderLabel.text = "Describe your need..." placeholderLabel.font = UIFont.init(name: "Lato-Regular", size: 15.0) ?? UIFont.boldSystemFont(ofSize: 14.0) placeholderLabel.sizeToFit() descriptionTextView.addSubview(placeholderLabel) placeholderLabel.frame.origin = CGPoint(x: 5, y: (descriptionTextView.font?.pointSize)! / 2) placeholderLabel.textColor = UIColor.lightGray placeholderLabel.isHidden = !descriptionTextView.text.isEmpty } //Delegate Method. func textViewDidChange(_ textView: UITextView) { placeholderLabel.isHidden = !textView.text.isEmpty }
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