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
斯威夫特
这是一个Swiftui TextView使用UIVIewRepresentable，具有占位符功能和边界颜色
struct TextView: UIViewRepresentable {
@Binding var text: String
var placeholderText: String
var textStyle: UIFont.TextStyle
func makeUIView(context: Context) -> UITextView {
let textView = UITextView()
textView.font = UIFont.preferredFont(forTextStyle: textStyle)
textView.autocapitalizationType = .sentences
textView.isSelectable = true
textView.isUserInteractionEnabled = true
textView.delegate = context.coordinator
textView.layer.borderWidth = 0.6
textView.layer.borderColor = UIColor.lightGray.cgColor
textView.layer.cornerRadius = 10
textView.text = placeholderText
textView.textColor = UIColor.lightGray
return textView
}
func updateUIView(_ uiView: UITextView, context: Context) {
uiView.text = text
uiView.font = UIFont.preferredFont(forTextStyle: textStyle)
}
func makeCoordinator() -> Coordinator {
Coordinator(self)
}
class Coordinator: NSObject, UITextViewDelegate {
var parent: TextView
init(_ parent: TextView) {
self.parent = parent
}
func textViewDidChange(_ textView: UITextView) {
self.parent.text = textView.text
}
func textViewDidBeginEditing(_ textView: UITextView) {
if textView.textColor == UIColor.lightGray {
textView.text = nil
textView.textColor = UIColor.black
}
}
func textViewDidEndEditing(_ textView: UITextView) {
if textView.text.isEmpty {
textView.text = self.parent.placeholderText
textView.textColor = UIColor.lightGray
}
}
}
}
然后在你的视图中你可以这样使用它
TextView(text: self.$viewModel.addPostCommentText, placeholderText: "Share your story about this cash", textStyle: .body)
.padding()
.frame(height: 150)
其他回答
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。
Swift 4更新
UITextView本身没有占位符属性，所以你必须用UITextViewDelegate方法来创建和操作一个。我建议使用下面的解决方案#1或#2，这取决于所需的行为。
注意:对于任何一种解决方案，都需要将UITextViewDelegate添加到类中，并设置textView.delegate = self来使用文本视图的委托方法。
解决方案#1 -如果你想让占位符在用户选择文本视图时立即消失:
首先将UITextView设置为包含占位符文本，并将其设置为浅灰色，以模拟UITextField的占位符文本的外观。要么在viewDidLoad中这样做，要么在文本视图创建时这样做。
textView.text = "Placeholder"
textView.textColor = UIColor.lightGray
然后，当用户开始编辑文本视图时，如果文本视图包含一个占位符(即，如果其文本颜色是浅灰色)，则清除占位符文本，并将文本颜色设置为黑色，以便容纳用户的输入。
func textViewDidBeginEditing(_ textView: UITextView) {
if textView.textColor == UIColor.lightGray {
textView.text = nil
textView.textColor = UIColor.black
}
}
然后，当用户完成编辑文本视图并将其作为第一响应器时，如果文本视图为空，则通过重新添加占位符文本并将其颜色设置为浅灰色来重置其占位符。
func textViewDidEndEditing(_ textView: UITextView) {
if textView.text.isEmpty {
textView.text = "Placeholder"
textView.textColor = UIColor.lightGray
}
}
解决方案#2 -如果你想要占位符显示文本视图是空的，即使文本视图被选中:
首先在viewDidLoad中设置占位符:
textView.text = "Placeholder"
textView.textColor = UIColor.lightGray
textView.becomeFirstResponder()
textView.selectedTextRange = textView.textRange(from: textView.beginningOfDocument, to: textView.beginningOfDocument)
(注意:由于OP希望在视图加载时立即选择文本视图，所以我将文本视图选择合并到上面的代码中。如果这不是你想要的行为，你不希望在视图加载时选择文本视图，从上面的代码块中删除最后两行。)
然后使用shouldChangeTextInRange UITextViewDelegate方法，如下所示:
func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
// Combine the textView text and the replacement text to
// create the updated text string
let currentText:String = textView.text
let updatedText = (currentText as NSString).replacingCharacters(in: range, with: text)
// If updated text view will be empty, add the placeholder
// and set the cursor to the beginning of the text view
if updatedText.isEmpty {
textView.text = "Placeholder"
textView.textColor = UIColor.lightGray
textView.selectedTextRange = textView.textRange(from: textView.beginningOfDocument, to: textView.beginningOfDocument)
}
// Else if the text view's placeholder is showing and the
// length of the replacement string is greater than 0, set
// the text color to black then set its text to the
// replacement string
else if textView.textColor == UIColor.lightGray && !text.isEmpty {
textView.textColor = UIColor.black
textView.text = text
}
// For every other case, the text should change with the usual
// behavior...
else {
return true
}
// ...otherwise return false since the updates have already
// been made
return false
}
也实现textViewDidChangeSelection，以防止用户改变光标的位置，而占位符是可见的。(注意:textViewDidChangeSelection在视图加载之前被调用，所以如果窗口是可见的，只检查文本视图的颜色):
func textViewDidChangeSelection(_ textView: UITextView) {
if self.view.window != nil {
if textView.textColor == UIColor.lightGray {
textView.selectedTextRange = textView.textRange(from: textView.beginningOfDocument, to: textView.beginningOfDocument)
}
}
}
斯威夫特
这是一个Swiftui TextView使用UIVIewRepresentable，具有占位符功能和边界颜色
struct TextView: UIViewRepresentable {
@Binding var text: String
var placeholderText: String
var textStyle: UIFont.TextStyle
func makeUIView(context: Context) -> UITextView {
let textView = UITextView()
textView.font = UIFont.preferredFont(forTextStyle: textStyle)
textView.autocapitalizationType = .sentences
textView.isSelectable = true
textView.isUserInteractionEnabled = true
textView.delegate = context.coordinator
textView.layer.borderWidth = 0.6
textView.layer.borderColor = UIColor.lightGray.cgColor
textView.layer.cornerRadius = 10
textView.text = placeholderText
textView.textColor = UIColor.lightGray
return textView
}
func updateUIView(_ uiView: UITextView, context: Context) {
uiView.text = text
uiView.font = UIFont.preferredFont(forTextStyle: textStyle)
}
func makeCoordinator() -> Coordinator {
Coordinator(self)
}
class Coordinator: NSObject, UITextViewDelegate {
var parent: TextView
init(_ parent: TextView) {
self.parent = parent
}
func textViewDidChange(_ textView: UITextView) {
self.parent.text = textView.text
}
func textViewDidBeginEditing(_ textView: UITextView) {
if textView.textColor == UIColor.lightGray {
textView.text = nil
textView.textColor = UIColor.black
}
}
func textViewDidEndEditing(_ textView: UITextView) {
if textView.text.isEmpty {
textView.text = self.parent.placeholderText
textView.textColor = UIColor.lightGray
}
}
}
}
然后在你的视图中你可以这样使用它
TextView(text: self.$viewModel.addPostCommentText, placeholderText: "Share your story about this cash", textStyle: .body)
.padding()
.frame(height: 150)
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。
斯威夫特3.2
extension EditProfileVC:UITextViewDelegate{
func textViewDidBeginEditing(_ textView: UITextView) {
if textView.textColor == UIColor.lightGray {
textView.text = nil
textView.textColor = UIColor.black
}
}
func textViewDidEndEditing(_ textView: UITextView) {
if textView.text.isEmpty {
textView.text = "Placeholder"
textView.textColor = UIColor.lightGray
}
}
}
首先，当用户开始编辑textViewDidBeginEditing调用，然后检查如果文本灰色的颜色意味着用户没有写任何东西，然后设置为textview nil，并将用户文本的颜色更改为黑色。
当用户端编辑textViewDidEndEditing是调用和检查如果用户没有写任何在textview然后文本设置为灰色与文本“占位符”
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