我的应用程序使用UITextView。现在我想让UITextView有一个占位符，类似于你可以为UITextField设置的占位符。
如何做到这一点?
当前回答
下面是swift 3.1的代码
原始代码由杰森乔治在第一个答案。
不要忘记设置你的自定义类的TextView在接口生成器UIPlaceHolderTextView，然后设置占位符和占位符属性。
import UIKit
@IBDesignable
class UIPlaceHolderTextView: UITextView {
@IBInspectable var placeholder: String = ""
@IBInspectable var placeholderColor: UIColor = UIColor.lightGray
private let uiPlaceholderTextChangedAnimationDuration: Double = 0.05
private let defaultTagValue = 999
private var placeHolderLabel: UILabel?
override func awakeFromNib() {
super.awakeFromNib()
NotificationCenter.default.addObserver(
self,
selector: #selector(textChanged),
name: NSNotification.Name.UITextViewTextDidChange,
object: nil
)
}
override init(frame: CGRect, textContainer: NSTextContainer?) {
super.init(frame: frame, textContainer: textContainer)
NotificationCenter.default.addObserver(
self,
selector: #selector(textChanged),
name: NSNotification.Name.UITextViewTextDidChange,
object: nil
)
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
NotificationCenter.default.addObserver(
self,
selector: #selector(textChanged),
name: NSNotification.Name.UITextViewTextDidChange,
object: nil
)
}
deinit {
NotificationCenter.default.removeObserver(
self,
name: NSNotification.Name.UITextViewTextDidChange,
object: nil
)
}
@objc private func textChanged() {
guard !placeholder.isEmpty else {
return
}
UIView.animate(withDuration: uiPlaceholderTextChangedAnimationDuration) {
if self.text.isEmpty {
self.viewWithTag(self.defaultTagValue)?.alpha = CGFloat(1.0)
}
else {
self.viewWithTag(self.defaultTagValue)?.alpha = CGFloat(0.0)
}
}
}
override var text: String! {
didSet{
super.text = text
textChanged()
}
}
override func draw(_ rect: CGRect) {
if !placeholder.isEmpty {
if placeHolderLabel == nil {
placeHolderLabel = UILabel.init(frame: CGRect(x: 0, y: 8, width: bounds.size.width - 16, height: 0))
placeHolderLabel!.lineBreakMode = .byWordWrapping
placeHolderLabel!.numberOfLines = 0
placeHolderLabel!.font = font
placeHolderLabel!.backgroundColor = UIColor.clear
placeHolderLabel!.textColor = placeholderColor
placeHolderLabel!.alpha = 0
placeHolderLabel!.tag = defaultTagValue
self.addSubview(placeHolderLabel!)
}
placeHolderLabel!.text = placeholder
placeHolderLabel!.sizeToFit()
self.sendSubview(toBack: placeHolderLabel!)
if text.isEmpty && !placeholder.isEmpty {
viewWithTag(defaultTagValue)?.alpha = 1.0
}
}
super.draw(rect)
}
}
其他回答
修改占位符文本颜色最简单的方法是通过XCode故事板接口构建器。选择感兴趣的UITextField并打开右侧的标识检查器。单击User Defined Runtime Attributes中的加号，并添加一个新行，其中Key Path为_placeholderLabel。输入颜色和值到你想要的颜色。
模拟本机占位符
一个常见的抱怨是iOS没有为文本视图提供原生占位符功能。下面的UITextView扩展试图通过提供人们期望从本机特性获得的便利来解决这个问题，只需要一行代码就可以向textview实例添加占位符。
这个解决方案的缺点是，因为它菊花链委托调用，它很容易(不太可能)在iOS更新中更改UITextViewDelegate协议。具体来说，如果iOS添加了新的协议方法，并且你在带有占位符的文本视图的委托中实现了它们中的任何一个，这些方法将不会被调用，除非你也更新了扩展来转发这些调用。
或者，内联占位符的答案是一个坚如磐石的和简单的可以。
使用例子:
•如果获得占位符的文本视图没有使用UITextViewDelegate:
/* Swift 3 */
class NoteViewController : UIViewController {
@IBOutlet weak var noteView: UITextView!
override func viewDidLoad() {
noteView.addPlaceholder("Enter some text...", color: UIColor.lightGray)
}
}
-- 或者——
•如果获得占位符的文本视图使用了UITextViewDelegate:
/* Swift 3 */
class NoteViewController : UIViewController, UITextViewDelegate {
@IBOutlet weak var noteView: UITextView!
override func viewDidLoad() {
noteView.addPlaceholder("Phone #", color: UIColor.lightGray, delegate: self)
}
}
实现(UITextView扩展):
/* Swift 3 */
extension UITextView: UITextViewDelegate
{
func addPlaceholder(_ placeholderText : String,
color : UIColor? = UIColor.lightGray,
delegate : UITextViewDelegate? = nil) {
self.delegate = self // Make receiving textview instance a delegate
let placeholder = UITextView() // Need delegate storage ULabel doesn't provide
placeholder.isUserInteractionEnabled = false //... so we *simulate* UILabel
self.addSubview(placeholder) // Add to text view instance's view tree
placeholder.sizeToFit() // Constrain to fit inside parent text view
placeholder.tintColor = UIColor.clear // Unused in textviews. Can host our 'tag'
placeholder.frame.origin = CGPoint(x: 5, y: 0) // Don't cover I-beam cursor
placeholder.delegate = delegate // Use as cache for caller's delegate
placeholder.font = UIFont.italicSystemFont(ofSize: (self.font?.pointSize)!)
placeholder.text = placeholderText
placeholder.textColor = color
}
func findPlaceholder() -> UITextView? { // find placeholder by its tag
for subview in self.subviews {
if let textview = subview as? UITextView {
if textview.tintColor == UIColor.clear { // sneaky tagging scheme
return textview
}
}
}
return nil
}
/*
* Safely daisychain to caller delegate methods as appropriate...
*/
public func textViewDidChange(_ textView: UITextView) { // ← need this delegate method
if let placeholder = findPlaceholder() {
placeholder.isHidden = !self.text.isEmpty // ← ... to do this
placeholder.delegate?.textViewDidChange?(textView)
}
}
/*
* Since we're becoming a delegate on behalf of this placeholder-enabled
* text view instance, we must forward *all* that protocol's activity expected
* by the instance, not just the particular optional protocol method we need to
* intercept, above.
*/
public func textViewDidEndEditing(_ textView: UITextView) {
if let placeholder = findPlaceholder() {
placeholder.delegate?.textViewDidEndEditing?(textView)
}
}
public func textViewDidBeginEditing(_ textView: UITextView) {
if let placeholder = findPlaceholder() {
placeholder.delegate?.textViewDidBeginEditing?(textView)
}
}
public func textViewDidChangeSelection(_ textView: UITextView) {
if let placeholder = findPlaceholder() {
placeholder.delegate?.textViewDidChangeSelection?(textView)
}
}
public func textViewShouldEndEditing(_ textView: UITextView) -> Bool {
if let placeholder = findPlaceholder() {
guard let retval = placeholder.delegate?.textViewShouldEndEditing?(textView) else {
return true
}
return retval
}
return true
}
public func textViewShouldBeginEditing(_ textView: UITextView) -> Bool {
if let placeholder = findPlaceholder() {
guard let retval = placeholder.delegate?.textViewShouldBeginEditing?(textView) else {
return true
}
return retval
}
return true
}
public func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
if let placeholder = findPlaceholder() {
guard let retval = placeholder.delegate?.textView?(textView, shouldChangeTextIn: range, replacementText: text) else {
return true
}
return retval
}
return true
}
public func textView(_ textView: UITextView, shouldInteractWith URL: URL, in characterRange: NSRange, interaction: UITextItemInteraction) -> Bool {
if let placeholder = findPlaceholder() {
guard let retval = placeholder.delegate?.textView?(textView, shouldInteractWith: URL, in: characterRange, interaction:
interaction) else {
return true
}
return retval
}
return true
}
public func textView(_ textView: UITextView, shouldInteractWith textAttachment: NSTextAttachment, in characterRange: NSRange, interaction: UITextItemInteraction) -> Bool {
if let placeholder = findPlaceholder() {
guard let retval = placeholder.delegate?.textView?(textView, shouldInteractWith: textAttachment, in: characterRange, interaction: interaction) else {
return true
}
return retval
}
return true
}
}
1. 作为一个像UITextView这样的基本iOS类的扩展，重要的是要知道这段代码没有与任何不激活占位符的textview交互，例如textview实例没有被调用addPlaceholder()初始化
2. 支持占位符的文本视图透明地变成一个UITextViewDelegate来跟踪字符计数，以控制占位符可见性。如果一个委托被传递给addPlaceholder()，这段代码会将委托回调给该委托。
3.作者正在研究如何检查UITextViewDelegate协议并自动代理它，而不必硬编码每个方法。这将使代码免受方法签名更改和添加到协议中的新方法的影响。
你也可以创建一个新的类TextViewWithPlaceholder作为UITextView的子类。
(这段代码有点粗糙——但我认为它在正确的轨道上。)
@interface TextViewWithPlaceholder : UITextView
{
NSString *placeholderText; // make a property
UIColor *placeholderColor; // make a property
UIColor *normalTextColor; // cache text color here whenever you switch to the placeholderColor
}
- (void) setTextColor: (UIColor*) color
{
normalTextColor = color;
[super setTextColor: color];
}
- (void) updateForTextChange
{
if ([self.text length] == 0)
{
normalTextColor = self.textColor;
self.textColor = placeholderColor;
self.text = placeholderText;
}
else
{
self.textColor = normalTextColor;
}
}
在委托中，添加以下内容:
- (void)textViewDidChange:(UITextView *)textView
{
if ([textView respondsToSelector: @selector(updateForTextChange)])
{
[textView updateForTextChange];
}
}
下面是“SAMTextView”ObjC代码的Swift端口，作为对这个问题的第一批回答之一。我在iOS 8上进行了测试。我调整了一些东西，包括占位符文本的位置的边界偏移，因为原来的位置太高，太右了(在那个帖子的一个评论中使用了建议)。
我知道有很多简单的解决方案，但我喜欢子类化UITextView的方法，因为它是可重用的，而且我不必在使用它的机制时使类变得混乱。
斯威夫特2.2:
import UIKit
class PlaceholderTextView: UITextView {
@IBInspectable var placeholderColor: UIColor = UIColor.lightGrayColor()
@IBInspectable var placeholderText: String = ""
override var font: UIFont? {
didSet {
setNeedsDisplay()
}
}
override var contentInset: UIEdgeInsets {
didSet {
setNeedsDisplay()
}
}
override var textAlignment: NSTextAlignment {
didSet {
setNeedsDisplay()
}
}
override var text: String? {
didSet {
setNeedsDisplay()
}
}
override var attributedText: NSAttributedString? {
didSet {
setNeedsDisplay()
}
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setUp()
}
override init(frame: CGRect, textContainer: NSTextContainer?) {
super.init(frame: frame, textContainer: textContainer)
}
private func setUp() {
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(PlaceholderTextView.textChanged(_:)),
name: UITextViewTextDidChangeNotification, object: self)
}
func textChanged(notification: NSNotification) {
setNeedsDisplay()
}
func placeholderRectForBounds(bounds: CGRect) -> CGRect {
var x = contentInset.left + 4.0
var y = contentInset.top + 9.0
let w = frame.size.width - contentInset.left - contentInset.right - 16.0
let h = frame.size.height - contentInset.top - contentInset.bottom - 16.0
if let style = self.typingAttributes[NSParagraphStyleAttributeName] as? NSParagraphStyle {
x += style.headIndent
y += style.firstLineHeadIndent
}
return CGRect(x: x, y: y, width: w, height: h)
}
override func drawRect(rect: CGRect) {
if text!.isEmpty && !placeholderText.isEmpty {
let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.alignment = textAlignment
let attributes: [ String: AnyObject ] = [
NSFontAttributeName : font!,
NSForegroundColorAttributeName : placeholderColor,
NSParagraphStyleAttributeName : paragraphStyle]
placeholderText.drawInRect(placeholderRectForBounds(bounds), withAttributes: attributes)
}
super.drawRect(rect)
}
}
斯威夫特4.2:
import UIKit
class PlaceholderTextView: UITextView {
@IBInspectable var placeholderColor: UIColor = UIColor.lightGray
@IBInspectable var placeholderText: String = ""
override var font: UIFont? {
didSet {
setNeedsDisplay()
}
}
override var contentInset: UIEdgeInsets {
didSet {
setNeedsDisplay()
}
}
override var textAlignment: NSTextAlignment {
didSet {
setNeedsDisplay()
}
}
override var text: String? {
didSet {
setNeedsDisplay()
}
}
override var attributedText: NSAttributedString? {
didSet {
setNeedsDisplay()
}
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setUp()
}
override init(frame: CGRect, textContainer: NSTextContainer?) {
super.init(frame: frame, textContainer: textContainer)
}
private func setUp() {
NotificationCenter.default.addObserver(self,
selector: #selector(self.textChanged(notification:)),
name: Notification.Name("UITextViewTextDidChangeNotification"),
object: nil)
}
@objc func textChanged(notification: NSNotification) {
setNeedsDisplay()
}
func placeholderRectForBounds(bounds: CGRect) -> CGRect {
var x = contentInset.left + 4.0
var y = contentInset.top + 9.0
let w = frame.size.width - contentInset.left - contentInset.right - 16.0
let h = frame.size.height - contentInset.top - contentInset.bottom - 16.0
if let style = self.typingAttributes[NSAttributedString.Key.paragraphStyle] as? NSParagraphStyle {
x += style.headIndent
y += style.firstLineHeadIndent
}
return CGRect(x: x, y: y, width: w, height: h)
}
override func draw(_ rect: CGRect) {
if text!.isEmpty && !placeholderText.isEmpty {
let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.alignment = textAlignment
let attributes: [NSAttributedString.Key: Any] = [
NSAttributedString.Key(rawValue: NSAttributedString.Key.font.rawValue) : font!,
NSAttributedString.Key(rawValue: NSAttributedString.Key.foregroundColor.rawValue) : placeholderColor,
NSAttributedString.Key(rawValue: NSAttributedString.Key.paragraphStyle.rawValue) : paragraphStyle]
placeholderText.draw(in: placeholderRectForBounds(bounds: bounds), withAttributes: attributes)
}
super.draw(rect)
}
}
下面是swift 3.1的代码
原始代码由杰森乔治在第一个答案。
不要忘记设置你的自定义类的TextView在接口生成器UIPlaceHolderTextView，然后设置占位符和占位符属性。
import UIKit
@IBDesignable
class UIPlaceHolderTextView: UITextView {
@IBInspectable var placeholder: String = ""
@IBInspectable var placeholderColor: UIColor = UIColor.lightGray
private let uiPlaceholderTextChangedAnimationDuration: Double = 0.05
private let defaultTagValue = 999
private var placeHolderLabel: UILabel?
override func awakeFromNib() {
super.awakeFromNib()
NotificationCenter.default.addObserver(
self,
selector: #selector(textChanged),
name: NSNotification.Name.UITextViewTextDidChange,
object: nil
)
}
override init(frame: CGRect, textContainer: NSTextContainer?) {
super.init(frame: frame, textContainer: textContainer)
NotificationCenter.default.addObserver(
self,
selector: #selector(textChanged),
name: NSNotification.Name.UITextViewTextDidChange,
object: nil
)
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
NotificationCenter.default.addObserver(
self,
selector: #selector(textChanged),
name: NSNotification.Name.UITextViewTextDidChange,
object: nil
)
}
deinit {
NotificationCenter.default.removeObserver(
self,
name: NSNotification.Name.UITextViewTextDidChange,
object: nil
)
}
@objc private func textChanged() {
guard !placeholder.isEmpty else {
return
}
UIView.animate(withDuration: uiPlaceholderTextChangedAnimationDuration) {
if self.text.isEmpty {
self.viewWithTag(self.defaultTagValue)?.alpha = CGFloat(1.0)
}
else {
self.viewWithTag(self.defaultTagValue)?.alpha = CGFloat(0.0)
}
}
}
override var text: String! {
didSet{
super.text = text
textChanged()
}
}
override func draw(_ rect: CGRect) {
if !placeholder.isEmpty {
if placeHolderLabel == nil {
placeHolderLabel = UILabel.init(frame: CGRect(x: 0, y: 8, width: bounds.size.width - 16, height: 0))
placeHolderLabel!.lineBreakMode = .byWordWrapping
placeHolderLabel!.numberOfLines = 0
placeHolderLabel!.font = font
placeHolderLabel!.backgroundColor = UIColor.clear
placeHolderLabel!.textColor = placeholderColor
placeHolderLabel!.alpha = 0
placeHolderLabel!.tag = defaultTagValue
self.addSubview(placeHolderLabel!)
}
placeHolderLabel!.text = placeholder
placeHolderLabel!.sizeToFit()
self.sendSubview(toBack: placeHolderLabel!)
if text.isEmpty && !placeholder.isEmpty {
viewWithTag(defaultTagValue)?.alpha = 1.0
}
}
super.draw(rect)
}
}
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