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

我创建了一个实例变量来检查是否显示占位符:

BOOL showPlaceHolder;
UITextView * textView; // and also the textView

在viewDidLoad上设置:

[self setPlaceHolder]; 

下面是它的作用:

- (void)setPlaceholder
{
    textView.text = NSLocalizedString(@"Type your question here", @"placeholder");
    textView.textColor = [UIColor lightGrayColor];
    self.showPlaceHolder = YES; //we save the state so it won't disappear in case you want to re-edit it
}

我还创建了一个按钮来退出键盘。您不必这样做,但这里很酷的事情是,如果没有输入任何内容,占位符将再次显示

- (void)textViewDidBeginEditing:(UITextView *)txtView 
{
    self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"Done" style:UIBarButtonItemStyleDone target:self action:@selector(resignKeyboard)];
    if (self.showPlaceHolder == YES) 
    {
        textView.textColor = [UIColor blackColor];
        textView.text = @"";
        self.showPlaceHolder = NO;
    }
}

- (void)resignKeyboard 
{
    [textView resignFirstResponder];
    //here if you created a button like I did to resign the keyboard, you should hide it
    if (textView.text.length == 0) {
        [self setPlaceholder];
    }       
}

其他回答

我做了我自己版本的UITextView的子类。我喜欢Sam Soffes使用通知的想法,但我不喜欢drawRect: overwrite。对我来说太过分了。我认为我做了一个非常干净的实现。

你可以看看我的子类。还包括一个演示项目。


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。

我刚刚发现,在iOS 10中,你现在可以将UITextView转换为方法的UITextField,并在方法中设置占位符。刚试过,它不需要子类化UITextView就能工作。

下面是一个对我有用的例子:

-(void)customizeTextField:(UITextField *)textField placeholder:(NSString *)pText withColor:(UIColor *)pTextColor{

        textField.attributedPlaceholder = [[NSAttributedString alloc]
                                          initWithString:pText
                                          attributes:@{NSForegroundColorAttributeName:pTextColor}];
    }

为了将它用于UITextView,你只需要将它传递给方法,使用像这样的类型转换:

[self customizeTextField:(UITextField*)_myTextView placeholder:@"Placeholder" withColor:[UIColor blackColor]];

注:经过测试,我发现这个解决方案在iOS9上也很好。但是会在iOS8.x上导致崩溃

我建议使用pod 'UITextView+Placeholder'

pod 'UITextView+Placeholder'

在代码中

#import "UITextView+Placeholder.h"

////    

UITextView *textView = [[UITextView alloc] init];
textView.placeholder = @"How are you?";
textView.placeholderColor = [UIColor lightGrayColor];

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)
    }
}