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
我相信这是一个非常干净的解决方案。它在实际文本视图下面添加了一个虚拟文本视图，并根据实际文本视图中的文本显示或隐藏它:
import Foundation
import UIKit
class TextViewWithPlaceholder: UITextView {
private var placeholderTextView: UITextView = UITextView()
var placeholder: String? {
didSet {
placeholderTextView.text = placeholder
}
}
override var text: String! {
didSet {
placeholderTextView.isHidden = text.isEmpty == false
}
}
override init(frame: CGRect, textContainer: NSTextContainer?) {
super.init(frame: frame, textContainer: textContainer)
commonInit()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
commonInit()
}
private func commonInit() {
applyCommonTextViewAttributes(to: self)
configureMainTextView()
addPlaceholderTextView()
NotificationCenter.default.addObserver(self,
selector: #selector(textDidChange),
name: UITextView.textDidChangeNotification,
object: nil)
}
func addPlaceholderTextView() {
applyCommonTextViewAttributes(to: placeholderTextView)
configurePlaceholderTextView()
insertSubview(placeholderTextView, at: 0)
}
private func applyCommonTextViewAttributes(to textView: UITextView) {
textView.translatesAutoresizingMaskIntoConstraints = false
textView.textContainer.lineFragmentPadding = 0
textView.textContainerInset = UIEdgeInsets(top: 10,
left: 10,
bottom: 10,
right: 10)
}
private func configureMainTextView() {
// Do any configuration of the actual text view here
}
private func configurePlaceholderTextView() {
placeholderTextView.text = placeholder
placeholderTextView.font = font
placeholderTextView.textColor = UIColor.lightGray
placeholderTextView.frame = bounds
placeholderTextView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
}
override func layoutSubviews() {
super.layoutSubviews()
placeholderTextView.frame = bounds
}
@objc func textDidChange() {
placeholderTextView.isHidden = !text.isEmpty
}
}
其他回答
我不知道为什么人们会把这个问题复杂化....这是相当直接和简单的。下面是UITextView的一个子类，它提供了所请求的功能。
- (void)customInit
{
self.contentMode = UIViewContentModeRedraw;
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChanged:) name:UITextViewTextDidChangeNotification object:nil];
}
- (void)textChanged:(NSNotification *)notification
{
if (notification.object == self) {
if(self.textStorage.length != 0 || !self.textStorage.length) {
[self setNeedsDisplay];
}
}
}
#pragma mark - Setters
- (void)setPlaceholderText:(NSString *)placeholderText withFont:(UIFont *)font
{
self.placeholderText = placeholderText;
self.placeholderTextFont = font;
}
- (void)drawRect:(CGRect)rect
{
[super drawRect:rect];
[[UIColor lightGrayColor] setFill];
if (self.textStorage.length != 0) {
return;
}
CGRect inset = CGRectInset(rect, 8, 8);//Default rect insets for textView
NSDictionary *attributes = @{NSFontAttributeName: self.placeholderTextFont, NSForegroundColorAttributeName: [UIColor grayColor]};
[self.placeholderText drawInRect:inset withAttributes:attributes];
}`
可能是UITextView占位符实现的最简单的开箱即用的解决方案，不会遭受:
使用UILabel而不是UITextView，这可能会有不同的表现 切换到和从占位符“UITextView”拷贝，将捕获第一个键入的字符将从主UITextView控件丢失 打乱主UITextView控件的文本内容，将占位符替换为空字符串或第一个键入的字符。边界情况是，如果用户输入占位符文本，一些建议的实现将把它作为一个占位符本身。
斯威夫特5:
import UIKit
import SnapKit
import RxSwift
import RxCocoa
class TextAreaView: UIView {
let textArea = UITextView()
let textAreaPlaceholder = UITextView()
override init(frame: CGRect) {
super.init(frame: frame)
commonSetup()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
commonSetup()
}
private func commonSetup() {
addSubview(textAreaPlaceholder)
addSubview(textArea)
textArea.isScrollEnabled = false
textArea.delegate = self
textAreaPlaceholder.isScrollEnabled = false
textAreaPlaceholder.textColor = UIColor.lightGray
textArea.snp.makeConstraints { make in
make.top.bottom.leading.trailing.equalToSuperview()
}
textAreaPlaceholder.snp.makeConstraints { make in
make.top.bottom.leading.trailing.equalTo(textArea.snp.top)
}
textAreaPlaceholder.text = "Placeholder"
updatePlaceholder()
}
func updatePlaceholder() {
if textArea.text.count > 0 {
textArea.alpha = 1.0
} else {
textArea.alpha = 0.0
}
}
}
extension TextAreaView: UITextViewDelegate {
func textViewDidChange(_ textView: UITextView) {
updatePlaceholder()
}
}
与这篇文章中几乎所有的答案相反，UITextView确实有一个占位符属性。由于我无法理解的原因，它只在IB中出现，例如:
<userDefinedRuntimeAttributes>
<userDefinedRuntimeAttribute type="string" keyPath="placeholder" value="My Placeholder"/>
</userDefinedRuntimeAttributes>
因此，如果你正在使用故事板，一个静态占位符就足够了，只需在检查器上设置属性。
你也可以像这样在代码中设置这个属性:
textView.setValue("My Placeholder", forKeyPath: "placeholder")
它的多云天气，这是通过私有API访问，因为属性是暴露的。
我还没有尝试过用这种方法提交。但我将很快以这种方式提交，并将相应地更新这个答案。
更新:
我已经在多个版本中发布了这个代码，苹果没有任何问题。
更新: 这将只适用于Xcode pre 11.2
我相信这是一个非常干净的解决方案。它在实际文本视图下面添加了一个虚拟文本视图，并根据实际文本视图中的文本显示或隐藏它:
import Foundation
import UIKit
class TextViewWithPlaceholder: UITextView {
private var placeholderTextView: UITextView = UITextView()
var placeholder: String? {
didSet {
placeholderTextView.text = placeholder
}
}
override var text: String! {
didSet {
placeholderTextView.isHidden = text.isEmpty == false
}
}
override init(frame: CGRect, textContainer: NSTextContainer?) {
super.init(frame: frame, textContainer: textContainer)
commonInit()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
commonInit()
}
private func commonInit() {
applyCommonTextViewAttributes(to: self)
configureMainTextView()
addPlaceholderTextView()
NotificationCenter.default.addObserver(self,
selector: #selector(textDidChange),
name: UITextView.textDidChangeNotification,
object: nil)
}
func addPlaceholderTextView() {
applyCommonTextViewAttributes(to: placeholderTextView)
configurePlaceholderTextView()
insertSubview(placeholderTextView, at: 0)
}
private func applyCommonTextViewAttributes(to textView: UITextView) {
textView.translatesAutoresizingMaskIntoConstraints = false
textView.textContainer.lineFragmentPadding = 0
textView.textContainerInset = UIEdgeInsets(top: 10,
left: 10,
bottom: 10,
right: 10)
}
private func configureMainTextView() {
// Do any configuration of the actual text view here
}
private func configurePlaceholderTextView() {
placeholderTextView.text = placeholder
placeholderTextView.font = font
placeholderTextView.textColor = UIColor.lightGray
placeholderTextView.frame = bounds
placeholderTextView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
}
override func layoutSubviews() {
super.layoutSubviews()
placeholderTextView.frame = bounds
}
@objc func textDidChange() {
placeholderTextView.isHidden = !text.isEmpty
}
}
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)
}
}
}
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