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
我是这样做的:
UITextView2.h
#import <UIKit/UIKit.h>
@interface UITextView2 : UITextView <UITextViewDelegate> {
NSString *placeholder;
UIColor *placeholderColor;
}
@property(nonatomic, retain) NSString *placeholder;
@property(nonatomic, retain) UIColor *placeholderColor;
-(void)textChanged:(NSNotification*)notif;
@end
UITextView2.m
@implementation UITextView2
@synthesize placeholder, placeholderColor;
- (id)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
[self setPlaceholder:@""];
[self setPlaceholderColor:[UIColor lightGrayColor]];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChanged:) name:UITextViewTextDidChangeNotification object:nil];
}
return self;
}
-(void)textChanged:(NSNotification*)notif {
if ([[self placeholder] length]==0)
return;
if ([[self text] length]==0) {
[[self viewWithTag:999] setAlpha:1];
} else {
[[self viewWithTag:999] setAlpha:0];
}
}
- (void)drawRect:(CGRect)rect {
if ([[self placeholder] length]>0) {
UILabel *l = [[UILabel alloc] initWithFrame:CGRectMake(8, 8, 0, 0)];
[l setFont:self.font];
[l setTextColor:self.placeholderColor];
[l setText:self.placeholder];
[l setAlpha:0];
[l setTag:999];
[self addSubview:l];
[l sizeToFit];
[self sendSubviewToBack:l];
[l release];
}
if ([[self text] length]==0 && [[self placeholder] length]>0) {
[[self viewWithTag:999] setAlpha:1];
}
[super drawRect:rect];
}
- (void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
[super dealloc];
}
@end
其他回答
我用swift写了一个类。您可以在需要时导入这个类。
import UIKit
public class CustomTextView： UITextView {
private struct Constants {
static let defaultiOSPlaceholderColor = UIColor(red: 0.0, green: 0.0, blue: 0.0980392, alpha: 0.22)
}
private let placeholderLabel: UILabel = UILabel()
private var placeholderLabelConstraints = [NSLayoutConstraint]()
@IBInspectable public var placeholder: String = "" {
didSet {
placeholderLabel.text = placeholder
}
}
@IBInspectable public var placeholderColor: UIColor = CustomTextView.Constants.defaultiOSPlaceholderColor {
didSet {
placeholderLabel.textColor = placeholderColor
}
}
override public var font: UIFont! {
didSet {
placeholderLabel.font = font
}
}
override public var textAlignment: NSTextAlignment {
didSet {
placeholderLabel.textAlignment = textAlignment
}
}
override public var text: String! {
didSet {
textDidChange()
}
}
override public var attributedText: NSAttributedString! {
didSet {
textDidChange()
}
}
override public 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() {
NSNotificationCenter.defaultCenter().addObserver(self,
selector: #selector(textDidChange),
name: UITextViewTextDidChangeNotification,
object: nil)
placeholderLabel.font = font
placeholderLabel.textColor = placeholderColor
placeholderLabel.textAlignment = textAlignment
placeholderLabel.text = placeholder
placeholderLabel.numberOfLines = 0
placeholderLabel.backgroundColor = UIColor.clearColor()
placeholderLabel.translatesAutoresizingMaskIntoConstraints = false
addSubview(placeholderLabel)
updateConstraintsForPlaceholderLabel()
}
private func updateConstraintsForPlaceholderLabel() {
var newConstraints = NSLayoutConstraint.constraintsWithVisualFormat("H:|-(\(textContainerInset.left + textContainer.lineFragmentPadding))-[placeholder]",
options: [],
metrics: nil,
views: ["placeholder": placeholderLabel])
newConstraints += NSLayoutConstraint.constraintsWithVisualFormat("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.hidden = !text.isEmpty
}
public override func layoutSubviews() {
super.layoutSubviews()
placeholderLabel.preferredMaxLayoutWidth = textContainer.size.width - textContainer.lineFragmentPadding * 2.0
}
deinit {
NSNotificationCenter.defaultCenter().removeObserver(self,
name: UITextViewTextDidChangeNotification,
object: nil)
}
}
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。
- (void)textViewDidChange:(UITextView *)textView
{
placeholderLabel.hidden = YES;
}
在textview上放一个标签。
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。
我对bcd的解决方案做了一些小修改，以允许从Xib文件初始化、文本包装和保持背景颜色。希望它能为其他人省去麻烦。
UIPlaceHolderTextView.h:
#import <Foundation/Foundation.h>
IB_DESIGNABLE
@interface UIPlaceHolderTextView : UITextView
@property (nonatomic, retain) IBInspectable NSString *placeholder;
@property (nonatomic, retain) IBInspectable UIColor *placeholderColor;
-(void)textChanged:(NSNotification*)notification;
@end
UIPlaceHolderTextView.m:
#import "UIPlaceHolderTextView.h"
@interface UIPlaceHolderTextView ()
@property (nonatomic, retain) UILabel *placeHolderLabel;
@end
@implementation UIPlaceHolderTextView
CGFloat const UI_PLACEHOLDER_TEXT_CHANGED_ANIMATION_DURATION = 0.25;
- (void)dealloc
{
[[NSNotificationCenter defaultCenter] removeObserver:self];
#if __has_feature(objc_arc)
#else
[_placeHolderLabel release]; _placeHolderLabel = nil;
[_placeholderColor release]; _placeholderColor = nil;
[_placeholder release]; _placeholder = nil;
[super dealloc];
#endif
}
- (void)awakeFromNib
{
[super awakeFromNib];
// Use Interface Builder User Defined Runtime Attributes to set
// placeholder and placeholderColor in Interface Builder.
if (!self.placeholder) {
[self setPlaceholder:@""];
}
if (!self.placeholderColor) {
[self setPlaceholderColor:[UIColor lightGrayColor]];
}
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChanged:) name:UITextViewTextDidChangeNotification object:nil];
}
- (id)initWithFrame:(CGRect)frame
{
if( (self = [super initWithFrame:frame]) )
{
[self setPlaceholder:@""];
[self setPlaceholderColor:[UIColor lightGrayColor]];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChanged:) name:UITextViewTextDidChangeNotification object:nil];
}
return self;
}
- (void)textChanged:(NSNotification *)notification
{
if([[self placeholder] length] == 0)
{
return;
}
[UIView animateWithDuration:UI_PLACEHOLDER_TEXT_CHANGED_ANIMATION_DURATION animations:^{
if([[self text] length] == 0)
{
[[self viewWithTag:999] setAlpha:1];
}
else
{
[[self viewWithTag:999] setAlpha:0];
}
}];
}
- (void)setText:(NSString *)text {
[super setText:text];
[self textChanged:nil];
}
- (void)drawRect:(CGRect)rect
{
if( [[self placeholder] length] > 0 )
{
if (_placeHolderLabel == nil )
{
_placeHolderLabel = [[UILabel alloc] initWithFrame:CGRectMake(8,8,self.bounds.size.width - 16,0)];
_placeHolderLabel.lineBreakMode = NSLineBreakByWordWrapping;
_placeHolderLabel.numberOfLines = 0;
_placeHolderLabel.font = self.font;
_placeHolderLabel.backgroundColor = [UIColor clearColor];
_placeHolderLabel.textColor = self.placeholderColor;
_placeHolderLabel.alpha = 0;
_placeHolderLabel.tag = 999;
[self addSubview:_placeHolderLabel];
}
_placeHolderLabel.text = self.placeholder;
[_placeHolderLabel sizeToFit];
[self sendSubviewToBack:_placeHolderLabel];
}
if( [[self text] length] == 0 && [[self placeholder] length] > 0 )
{
[[self viewWithTag:999] setAlpha:1];
}
[super drawRect:rect];
}
@end
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