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
浮动的占位符
将占位符标签放置在文本视图之上,通过跟踪文本视图字符计数的变化来设置其字体、颜色和管理占位符可见性,这是简单、安全且可靠的。
斯威夫特5:
class NotesViewController : UIViewController {
@IBOutlet var textView : UITextView!
var placeholderLabel : UILabel!
override func viewDidLoad() {
super.viewDidLoad()
textView.delegate = self
placeholderLabel = UILabel()
placeholderLabel.text = "Enter some text..."
placeholderLabel.font = .italicSystemFont(ofSize: (textView.font?.pointSize)!)
placeholderLabel.sizeToFit()
textView.addSubview(placeholderLabel)
placeholderLabel.frame.origin = CGPoint(x: 5, y: (textView.font?.pointSize)! / 2)
placeholderLabel.textColor = .tertiaryLabel
placeholderLabel.isHidden = !textView.text.isEmpty
}
}
extension NotesViewController : UITextViewDelegate {
func textViewDidChange(_ textView: UITextView) {
placeholderLabel.isHidden = !textView.text.isEmpty
}
}
在swift2.2:
public class CustomTextView: UITextView {
private struct Constants {
static let defaultiOSPlaceholderColor = UIColor(red: 0.0, green: 0.0, blue: 0.0980392, alpha: 0.22)
}
private let placeholderLabel: UILabel = UILabel()
private var placeholderLabelConstraints = [NSLayoutConstraint]()
@IBInspectable public var placeholder: String = "" {
didSet {
placeholderLabel.text = placeholder
}
}
@IBInspectable public var placeholderColor: UIColor = CustomTextView.Constants.defaultiOSPlaceholderColor {
didSet {
placeholderLabel.textColor = placeholderColor
}
}
override public var font: UIFont! {
didSet {
placeholderLabel.font = font
}
}
override public var textAlignment: NSTextAlignment {
didSet {
placeholderLabel.textAlignment = textAlignment
}
}
override public var text: String! {
didSet {
textDidChange()
}
}
override public var attributedText: NSAttributedString! {
didSet {
textDidChange()
}
}
override public var textContainerInset: UIEdgeInsets {
didSet {
updateConstraintsForPlaceholderLabel()
}
}
override public init(frame: CGRect, textContainer: NSTextContainer?) {
super.init(frame: frame, textContainer: textContainer)
commonInit()
}
required public init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
commonInit()
}
private func commonInit() {
NSNotificationCenter.defaultCenter().addObserver(self,
selector: #selector(textDidChange),
name: UITextViewTextDidChangeNotification,
object: nil)
placeholderLabel.font = font
placeholderLabel.textColor = placeholderColor
placeholderLabel.textAlignment = textAlignment
placeholderLabel.text = placeholder
placeholderLabel.numberOfLines = 0
placeholderLabel.backgroundColor = UIColor.clearColor()
placeholderLabel.translatesAutoresizingMaskIntoConstraints = false
addSubview(placeholderLabel)
updateConstraintsForPlaceholderLabel()
}
private func updateConstraintsForPlaceholderLabel() {
var newConstraints = NSLayoutConstraint.constraintsWithVisualFormat("H:|-(\(textContainerInset.left + textContainer.lineFragmentPadding))-[placeholder]",
options: [],
metrics: nil,
views: ["placeholder": placeholderLabel])
newConstraints += NSLayoutConstraint.constraintsWithVisualFormat("V:|-(\(textContainerInset.top))-[placeholder]",
options: [],
metrics: nil,
views: ["placeholder": placeholderLabel])
newConstraints.append(NSLayoutConstraint(
item: placeholderLabel,
attribute: .Width,
relatedBy: .Equal,
toItem: self,
attribute: .Width,
multiplier: 1.0,
constant: -(textContainerInset.left + textContainerInset.right + textContainer.lineFragmentPadding * 2.0)
))
removeConstraints(placeholderLabelConstraints)
addConstraints(newConstraints)
placeholderLabelConstraints = newConstraints
}
@objc private func textDidChange() {
placeholderLabel.hidden = !text.isEmpty
}
public override func layoutSubviews() {
super.layoutSubviews()
placeholderLabel.preferredMaxLayoutWidth = textContainer.size.width - textContainer.lineFragmentPadding * 2.0
}
deinit {
NSNotificationCenter.defaultCenter().removeObserver(self,
name: UITextViewTextDidChangeNotification,
object: nil)
}
}
在swift3:
import UIKit
类 CustomTextView: { UITextView
private struct Constants {
static let defaultiOSPlaceholderColor = UIColor(red: 0.0, green: 0.0, blue: 0.0980392, alpha: 0.22)
}
private let placeholderLabel: UILabel = UILabel()
private var placeholderLabelConstraints = [NSLayoutConstraint]()
@IBInspectable public var placeholder: String = "" {
didSet {
placeholderLabel.text = placeholder
}
}
@IBInspectable public var placeholderColor: UIColor = CustomTextView.Constants.defaultiOSPlaceholderColor {
didSet {
placeholderLabel.textColor = placeholderColor
}
}
override public var font: UIFont! {
didSet {
placeholderLabel.font = font
}
}
override public var textAlignment: NSTextAlignment {
didSet {
placeholderLabel.textAlignment = textAlignment
}
}
override public var text: String! {
didSet {
textDidChange()
}
}
override public var attributedText: NSAttributedString! {
didSet {
textDidChange()
}
}
override public var textContainerInset: UIEdgeInsets {
didSet {
updateConstraintsForPlaceholderLabel()
}
}
override public init(frame: CGRect, textContainer: NSTextContainer?) {
super.init(frame: frame, textContainer: textContainer)
commonInit()
}
required public init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
commonInit()
}
private func commonInit() {
NotificationCenter.default.addObserver(self,
selector: #selector(textDidChange),
name: NSNotification.Name.UITextViewTextDidChange,
object: nil)
placeholderLabel.font = font
placeholderLabel.textColor = placeholderColor
placeholderLabel.textAlignment = textAlignment
placeholderLabel.text = placeholder
placeholderLabel.numberOfLines = 0
placeholderLabel.backgroundColor = UIColor.clear
placeholderLabel.translatesAutoresizingMaskIntoConstraints = false
addSubview(placeholderLabel)
updateConstraintsForPlaceholderLabel()
}
private func updateConstraintsForPlaceholderLabel() {
var newConstraints = NSLayoutConstraint.constraints(withVisualFormat: "H:|-(\(textContainerInset.left + textContainer.lineFragmentPadding))-[placeholder]",
options: [],
metrics: nil,
views: ["placeholder": placeholderLabel])
newConstraints += NSLayoutConstraint.constraints(withVisualFormat: "V:|-(\(textContainerInset.top))-[placeholder]",
options: [],
metrics: nil,
views: ["placeholder": placeholderLabel])
newConstraints.append(NSLayoutConstraint(
item: placeholderLabel,
attribute: .width,
relatedBy: .equal,
toItem: self,
attribute: .width,
multiplier: 1.0,
constant: -(textContainerInset.left + textContainerInset.right + textContainer.lineFragmentPadding * 2.0)
))
removeConstraints(placeholderLabelConstraints)
addConstraints(newConstraints)
placeholderLabelConstraints = newConstraints
}
@objc private func textDidChange() {
placeholderLabel.isHidden = !text.isEmpty
}
public override func layoutSubviews() {
super.layoutSubviews()
placeholderLabel.preferredMaxLayoutWidth = textContainer.size.width - textContainer.lineFragmentPadding * 2.0
}
deinit {
NotificationCenter.default.removeObserver(self,
name: NSNotification.Name.UITextViewTextDidChange,
object: nil)
}
}
我用swift写了一个类。您需要在需要的时候导入这个类。
由于声誉问题,我不能发表评论。在@clearlight answer中增加一个委托需求。
func textViewDidBeginEditing(_ textView: UITextView) {
cell.placeholderLabel.isHidden = !textView.text.isEmpty
}
是需要
因为textViewDidChange不是第一次被调用
这里有一些东西可以被放到UIStackView中,它会使用内部高度约束来调整自己的大小。可能需要调整以适应特定的需求。
import UIKit
public protocol PlaceholderTextViewDelegate: class {
func placeholderTextViewTextChanged(_ textView: PlaceholderTextView, text: String)
}
public class PlaceholderTextView: UIView {
public weak var delegate: PlaceholderTextViewDelegate?
private var heightConstraint: NSLayoutConstraint?
public override init(frame: CGRect) {
self.allowsNewLines = true
super.init(frame: frame)
self.heightConstraint = self.heightAnchor.constraint(equalToConstant: 0)
self.heightConstraint?.isActive = true
self.addSubview(self.placeholderTextView)
self.addSubview(self.textView)
self.pinToCorners(self.placeholderTextView)
self.pinToCorners(self.textView)
self.updateHeight()
}
public override func didMoveToSuperview() {
super.didMoveToSuperview()
self.updateHeight()
}
private func pinToCorners(_ view: UIView) {
NSLayoutConstraint.activate([
view.leadingAnchor.constraint(equalTo: self.leadingAnchor),
view.trailingAnchor.constraint(equalTo: self.trailingAnchor),
view.topAnchor.constraint(equalTo: self.topAnchor),
view.bottomAnchor.constraint(equalTo: self.bottomAnchor)
])
}
// Accessors
public var text: String? {
didSet {
self.textView.text = text
self.textViewDidChange(self.textView)
self.updateHeight()
}
}
public var textColor: UIColor? {
didSet {
self.textView.textColor = textColor
self.updateHeight()
}
}
public var font: UIFont? {
didSet {
self.textView.font = font
self.placeholderTextView.font = font
self.updateHeight()
}
}
public override var tintColor: UIColor? {
didSet {
self.textView.tintColor = tintColor
self.placeholderTextView.tintColor = tintColor
}
}
public var placeholderText: String? {
didSet {
self.placeholderTextView.text = placeholderText
self.updateHeight()
}
}
public var placeholderTextColor: UIColor? {
didSet {
self.placeholderTextView.textColor = placeholderTextColor
self.updateHeight()
}
}
public var allowsNewLines: Bool
public required init?(coder _: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
private lazy var textView: UITextView = self.newTextView()
private lazy var placeholderTextView: UITextView = self.newTextView()
private func newTextView() -> UITextView {
let textView = UITextView()
textView.translatesAutoresizingMaskIntoConstraints = false
textView.isScrollEnabled = false
textView.delegate = self
textView.backgroundColor = .clear
return textView
}
private func updateHeight() {
let maxSize = CGSize(width: self.frame.size.width, height: .greatestFiniteMagnitude)
let textViewSize = self.textView.sizeThatFits(maxSize)
let placeholderSize = self.placeholderTextView.sizeThatFits(maxSize)
let maxHeight = ceil(CGFloat.maximum(textViewSize.height, placeholderSize.height))
self.heightConstraint?.constant = maxHeight
}
}
extension PlaceholderTextView: UITextViewDelegate {
public func textViewDidChangeSelection(_: UITextView) {
self.placeholderTextView.alpha = self.textView.text.isEmpty ? 1 : 0
self.updateHeight()
}
public func textViewDidChange(_: UITextView) {
self.delegate?.placeholderTextViewTextChanged(self, text: self.textView.text)
}
public func textView(_: UITextView, shouldChangeTextIn _: NSRange,
replacementText text: String) -> Bool {
let containsNewLines = text.rangeOfCharacter(from: .newlines)?.isEmpty == .some(false)
guard !containsNewLines || self.allowsNewLines else { return false }
return true
}
}
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
}
}
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