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
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。
其他回答
如果你正在寻找一个简单的方法来实现这一点,试试我的方法:
- (BOOL)textViewShouldBeginEditing:(UITextView *)textView
{
if ([[textView text] isEqualToString:PLACE_HOLDER_TEXT]) {
textView.text = @"";
textView.textColor = [UIColor blackColor];
}
return YES;
}
-(BOOL)textViewShouldEndEditing:(UITextView *)textView
{
if ([[textView text] length] == 0) {
textView.text = PLACE_HOLDER_TEXT;
textView.textColor = [UIColor lightGrayColor];
}
return YES;
}
是的,就是它PLACE_HOLDER_TEXT是一个NSString包含你的占位符
一个更简单的方法是创建一个次要的UITextView,它具有与原始文本视图相同的所有属性,除了不同的textColor,并带有约束以确保它们保持对齐。然后当任何字符进入主文本视图时,隐藏克隆文本视图,否则显示带有一些文本的克隆文本视图。
这可以通过几种方式实现,但相对简单的方法是子类化UITextView并将所有这些逻辑保留在子类中。
所以,子类UITextView并允许它惰性地创建它的占位符视图
接口文件:
@interface FOOTextView : UITextView <UITextViewDelegate>
@property (nonatomic, copy) NSString *placeholderText;
- (void)checkPlaceholder;
@end
实现文件:
#import "FOOTextView.h"
@interface FOOTextView ()
@property (nonatomic, strong) UITextView *placeholderTextView;
@end
@implementation FOOTextView
- (void)checkPlaceholder {
// Hide the placeholder text view if we've got any text
self.placeholderTextView.hidden = (self.text.length > 0 || self.attributedText.length > 0);
}
- (void)setPlaceholderText:(NSString *)placeholderText {
_placeholderText = [placeholderText copy];
// Setup the placeholder text view if we haven't already
[self setupPlaceholderTextView];
// Apply the placeholder text to the placeholder text view
self.placeholderTextView.text = placeholderText;
}
- (void)setupPlaceholderTextView {
if (!self.placeholderTextView) {
// Setup the place holder text view, duplicating our visual setup
self.placeholderTextView = [[UITextView alloc] initWithFrame:CGRectZero];
self.placeholderTextView.translatesAutoresizingMaskIntoConstraints = NO;
self.placeholderTextView.textColor = self.placeholderTextColor ? self.placeholderTextColor : [UIColor colorWithRed:199.f/255.f green:199.f/255.f blue:205.f/255.f alpha:1.f];
self.placeholderTextView.userInteractionEnabled = NO;
self.placeholderTextView.font = self.font;
self.placeholderTextView.textAlignment = self.textAlignment;
self.placeholderTextView.backgroundColor = self.backgroundColor;
self.placeholderTextView.editable = NO;
// Our background color must be clear for the placeholder text view to show through
self.backgroundColor = [UIColor clearColor];
// Insert the placeholder text view into our superview, below ourself so it shows through
[self.superview insertSubview:self.placeholderTextView belowSubview:self];
// Setup constraints to ensure the placeholder text view stays aligned with us
NSLayoutConstraint *constraintCenterX = [NSLayoutConstraint constraintWithItem:self.placeholderTextView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeCenterX multiplier:1.f constant:0.f];
NSLayoutConstraint *constraintCenterY = [NSLayoutConstraint constraintWithItem:self.placeholderTextView attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeCenterY multiplier:1.f constant:0.f];
NSLayoutConstraint *constraintWidth = [NSLayoutConstraint constraintWithItem:self.placeholderTextView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeWidth multiplier:1.f constant:0.f];
NSLayoutConstraint *constraintHeight = [NSLayoutConstraint constraintWithItem:self.placeholderTextView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeHeight multiplier:1.f constant:0.f];
NSArray *constraints = @[constraintCenterX, constraintCenterY, constraintWidth, constraintHeight];
[self.superview addConstraints:constraints];
}
}
- (void)setPlaceholderTextColor:(UIColor *)placeholderTextColor {
_placeholderTextColor = placeholderTextColor;
self.placeholderTextView.textColor = _placeholderTextColor;
}
- (void)setBackgroundColor:(UIColor *)backgroundColor {
// We don't want a background color ourselves, instead we want our placeholder text view to have the desired background color
[self.placeholderTextView setBackgroundColor:backgroundColor];
}
- (void)removeFromSuperview {
// Ensure we also remove our placeholder text view
[self.placeholderTextView removeFromSuperview];
self.placeholderTextView = nil;
[super removeFromSuperview];
}
#pragma mark - Text View Delegation
- (void)textViewDidChange:(UITextView *)textView {
[self checkPlaceholder];
}
@end
使用上面的类,如果你设置了一个FOOTextView的委托实例到它自己,一切都将开箱工作:
FOOTextView *myTextView = ...
myTextView.placeholderText = @"What's on your mind?";
myTextView.placeholderTextColor = [UIColor lightGrayColor];
myTextView.delegate = myTextView;
如果你想另一个对象接管作为委托,那么你只需要在textViewDidChange: delegate方法中调用文本视图的checkPlaceholder方法,例如;
FOOTextView *myTextView = ...
myTextView.placeholderText = @"What's on your mind?";
myTextView.placeholderTextColor = [UIColor lightGrayColor];
myTextView.delegate = self;
self.myTextView = myTextView;
- (void)textViewDidChange:(UITextView *)textView {
// Call the checkPlaceholder method to update the visuals
[self.myTextView checkPlaceholder];
}
在代码行中使用它的简单方法:
取一个标签到。nib中的UITextView 将这个标签连接到你的代码, 在它。
- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text{
if (range.location>0 || text.length!=0) {
placeholderLabel1.hidden = YES;
}else{
placeholderLabel1.hidden = NO;
}
return YES;
}
我已经创建了一个快速3版本的最高排名的答案
你只需要做UITextView的子类化。
import UIKit
class UIPlaceHolderTextView: UITextView {
//MARK: - Properties
@IBInspectable var placeholder: String?
@IBInspectable var placeholderColor: UIColor?
var placeholderLabel: UILabel?
//MARK: - Initializers
override func awakeFromNib() {
super.awakeFromNib()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
// Use Interface Builder User Defined Runtime Attributes to set
// placeholder and placeholderColor in Interface Builder.
if self.placeholder == nil {
self.placeholder = ""
}
if self.placeholderColor == nil {
self.placeholderColor = UIColor.black
}
NotificationCenter.default.addObserver(self, selector: #selector(textChanged(_:)), name: NSNotification.Name.UITextViewTextDidChange, object: nil)
}
func textChanged(_ notification: Notification) -> Void {
if self.placeholder?.count == 0 {
return
}
UIView.animate(withDuration: 0.25) {
if self.text.count == 0 {
self.viewWithTag(999)?.alpha = 1
}
else {
self.viewWithTag(999)?.alpha = 0
}
}
}
// Only override draw() if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
override func draw(_ rect: CGRect) {
super.draw(rect)
if (self.placeholder?.count ?? 0) > 0 {
if placeholderLabel == nil {
placeholderLabel = UILabel.init()
placeholderLabel?.lineBreakMode = .byWordWrapping
placeholderLabel?.numberOfLines = 0
placeholderLabel?.font = self.font
placeholderLabel?.backgroundColor = self.backgroundColor
placeholderLabel?.textColor = self.placeholderColor
placeholderLabel?.alpha = 0
placeholderLabel?.tag = 999
self.addSubview(placeholderLabel!)
placeholderLabel?.translatesAutoresizingMaskIntoConstraints = false
placeholderLabel?.topAnchor.constraint(equalTo: self.topAnchor, constant: 7).isActive = true
placeholderLabel?.leftAnchor.constraint(equalTo: self.leftAnchor, constant: 4).isActive = true
placeholderLabel?.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
placeholderLabel?.rightAnchor.constraint(equalTo: self.rightAnchor).isActive = true
}
placeholderLabel?.text = self.placeholder
placeholderLabel?.sizeToFit()
self.sendSubview(toBack: self.placeholderLabel!)
}
if self.text.count == 0 && (self.placeholder?.count ?? 0) > 0 {
self.viewWithTag(999)?.alpha = 1
}
}
}
简单的Swift 3解决方案
添加UITextViewDelegate到类中
设置你的textview .delegate = self
创建placeholderLabel和位置它在你的textview
现在动画placeholderLabel。alpha在textViewDidChange:
func textViewDidChange(_ textView: UITextView) {
let newAlpha: CGFloat = textView.text.isEmpty ? 1 : 0
if placeholderLabel.alpha != newAlpha {
UIView.animate(withDuration: 0.3) {
self.placeholderLabel.alpha = newAlpha
}
}
}
你可能不得不使用placeholderLabel位置来设置它,但这应该不会太难