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?
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
斯威夫特3.1
在尝试了所有快速的答案之后,这个答案将为我节省3个小时的研究时间。希望这能有所帮助。
确保你的textField(不管你有什么自定义名称)指向它在Storyboard中的委托,并且有一个@IBOutlet和你的customtextfield 将以下内容添加到viewDidLoad()中,加载视图时会出现:
告诉我什么看起来是占位符:
yourCustomTextField = "Start typing..."
yourCustomTextField.textColor = .lightGray
在viewDidLoad外部但在同一个类内部添加以下声明:UIViewController, UITextViewDelegate, UINavigationControllerDelegate
这段代码将使yourCustomTextField在输入textField时消失:
func textViewDidBeginEditing (_ textView: UITextView) {
if (textView.text == "Start typing...") {
textView.text = ""
textView.textColor = .black
}
textView.becomeFirstResponder()
}
func textViewDidEndEditing(_ textView: UITextView) {
if (textView.text == "") {
textView.text = "Start typing..."
textView.textColor = .lightGray
}
textView.resignFirstResponder()
}
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。 保持该文本与查看字段的文本属性的任何外部类完全分离。
欢迎提出改进建议。
编辑1:更新为重置占位符格式,如果实际文本以编程方式设置。
编辑2:现在可以以编程方式检索占位符文本颜色。
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 {
if showingPlaceholder {
removePlaceholderFormatting() // If the placeholder text is what's being changed, it's no longer the placeholder
}
super.text = newValue
}
}
@IBInspectable var placeholderText: String = ""
@IBInspectable var placeholderTextColor: UIColor = .placeholderText
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 public func becomeFirstResponder() -> Bool {
// If the current text is the placeholder, remove it
if showingPlaceholder {
text = nil
removePlaceholderFormatting()
}
return super.becomeFirstResponder()
}
override public func resignFirstResponder() -> Bool {
// If there's no text, put the placeholder back
if text.isEmpty {
showPlaceholderText()
}
return super.resignFirstResponder()
}
private func showPlaceholderText() {
text = placeholderText
showingPlaceholder = true
textColor = placeholderTextColor
}
private func removePlaceholderFormatting() {
showingPlaceholder = false
textColor = nil // Put the text back to the default, unmodified color
}
}
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)
}
}
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。
TextView占位符
import UIKit
@IBDesignable
open class KMPlaceholderTextView: UITextView {
private struct Constants {
static let defaultiOSPlaceholderColor = UIColor(red: 0.0, green: 0.0, blue: 0.0980392, alpha: 0.22)
}
public let placeholderLabel: UILabel = UILabel()
private var placeholderLabelConstraints = [NSLayoutConstraint]()
@IBInspectable open var placeholder: String = "" {
didSet {
placeholderLabel.text = placeholder
}
}
@IBInspectable open var placeholderColor: UIColor = KMPlaceholderTextView.Constants.defaultiOSPlaceholderColor {
didSet {
placeholderLabel.textColor = placeholderColor
}
}
override open var font: UIFont! {
didSet {
if placeholderFont == nil {
placeholderLabel.font = font
}
}
}
open var placeholderFont: UIFont? {
didSet {
let font = (placeholderFont != nil) ? placeholderFont : self.font
placeholderLabel.font = font
}
}
override open var textAlignment: NSTextAlignment {
didSet {
placeholderLabel.textAlignment = textAlignment
}
}
override open var text: String! {
didSet {
textDidChange()
}
}
override open var attributedText: NSAttributedString! {
didSet {
textDidChange()
}
}
override open 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() {
#if swift(>=4.2)
let notificationName = UITextView.textDidChangeNotification
#else
let notificationName = NSNotification.Name.UITextView.textDidChangeNotification
#endif
NotificationCenter.default.addObserver(self,
selector: #selector(textDidChange),
name: notificationName,
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
self.layoutIfNeeded()
}
open override func layoutSubviews() {
super.layoutSubviews()
placeholderLabel.preferredMaxLayoutWidth = textContainer.size.width - textContainer.lineFragmentPadding * 2.0
}
deinit {
#if swift(>=4.2)
let notificationName = UITextView.textDidChangeNotification
#else
let notificationName = NSNotification.Name.UITextView.textDidChangeNotification
#endif
NotificationCenter.default.removeObserver(self,
name: notificationName,
object: nil)
}
}
使用
After looking through (and trying out) most of the proposed solutions to this seemingly obvious - but missing - feature of UITextView, the 'best' closest I found was that from BobDickinson. But I didnt like having to resort to a whole new subclass [I prefer drop-in categories for such simple functional additions], nor that it intercepted UITextViewDelegate methods, which is probably going to mess up your existing UITextView handling code. So here's my take on a drop-in category that'll work on any existing UITextView instance...
#import <objc/runtime.h>
// Private subclass needed to override placeholderRectForBounds: to correctly position placeholder
@interface _TextField : UITextField
@property UIEdgeInsets insets;
@end
@implementation _TextField
- (CGRect)placeholderRectForBounds:(CGRect)bounds
{
CGRect rect = [super placeholderRectForBounds:bounds];
return UIEdgeInsetsInsetRect(rect, _insets);
}
@end
@implementation UITextView (Placeholder)
static const void *KEY;
- (void)setPlaceholder:(NSString *)placeholder
{
_TextField *textField = objc_getAssociatedObject(self, &KEY);
if (!textField) {
textField = [_TextField.alloc initWithFrame:self.bounds];
textField.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
textField.userInteractionEnabled = NO;
textField.font = self.font;
textField.contentVerticalAlignment = UIControlContentVerticalAlignmentTop;
textField.insets = UIEdgeInsetsMake(self.textContainerInset.top,
self.textContainerInset.left + self.textContainer.lineFragmentPadding,
self.textContainerInset.bottom,
self.textContainerInset.right);
[self addSubview:textField];
[self sendSubviewToBack:textField];
objc_setAssociatedObject(self, &KEY, textField, OBJC_ASSOCIATION_RETAIN);
[NSNotificationCenter.defaultCenter addObserver:self selector:@selector(updatePlaceholder:) name:UITextViewTextDidChangeNotification object:nil];
}
textField.placeholder = placeholder;
}
- (NSString*)placeholder
{
UITextField *textField = objc_getAssociatedObject(self, &KEY);
return textField.placeholder;
}
- (void)updatePlaceholder:(NSNotification *)notification
{
UITextField *textField = objc_getAssociatedObject(self, &KEY);
textField.font = self.font;
[textField setAlpha:self.text.length? 0 : 1];
}
@end
它使用简单,只是显而易见的
UITextView *myTextView = UITextView.new;
...
myTextView.placeholder = @"enter text here";
它通过添加一个UITextField -在正确的位置-在你的UITextView后面,并利用它的占位符代替(因此你不必担心得到正确的颜色等),然后监听通知,每当你的UITextView被改变显示/隐藏这个UITextField(因此它不会干扰你现有的UITextViewDelegate调用)。这里面没有什么神奇的数字……: -)
objc_setAssociatedObject()/objc_getAssociatedObject()是为了避免必须子类化UITextView。[不幸的是,要正确地定位UITextField,有必要引入一个'private'子类,以覆盖placeholderRectForBounds:]
改编自BobDickinson的斯威夫特回答。