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
我找到了自己的解决方案
- (void)textViewDidBeginEditing:(UITextView *)textView
{
if ([textView.text isEqualToString:PLACEHOLDER_TEXT])
{
textView.textColor = [UIColor lightGrayColor];
dispatch_async(dispatch_get_main_queue(), ^
{
textView.selectedRange = NSMakeRange(0, 0);
});
}
else
{
textView.textColor = [UIColor blackColor];
}
[textView becomeFirstResponder];
}
- (void)textViewDidEndEditing:(UITextView *)textView
{
if ([textView.text isEqualToString:@""])
{
textView.text = PLACEHOLDER_TEXT;
textView.textColor = [UIColor lightGrayColor];
}
[textView resignFirstResponder];
}
- (BOOL)textView:(UITextView *)textView
shouldChangeTextInRange:(NSRange)range
replacementText:(NSString *)text
{
if (range.location == 0 && range.length == [[textView text] length] && [text isEqualToString:@""])
{
textView.text = PLACEHOLDER_TEXT;
textView.textColor = [UIColor lightGrayColor];
dispatch_async(dispatch_get_main_queue(), ^
{
textView.selectedRange = NSMakeRange(0, 0);
});
return NO;
}
if ([textView.text isEqualToString:PLACEHOLDER_TEXT])
{
textView.text = @"";
textView.textColor = [UIColor blackColor];
}
return YES;
}
其他回答
我对发布的任何解决方案都不太满意,因为它们有点重。向视图中添加视图并不理想(尤其是在drawRect:)。它们都有漏洞,这也是不可接受的。
这是我的解决方案:SAMTextView
SAMTextView.h
//
// SAMTextView.h
// SAMTextView
//
// Created by Sam Soffes on 8/18/10.
// Copyright 2010-2013 Sam Soffes. All rights reserved.
//
#import <UIKit/UIKit.h>
/**
UITextView subclass that adds placeholder support like UITextField has.
*/
@interface SAMTextView : UITextView
/**
The string that is displayed when there is no other text in the text view.
The default value is `nil`.
*/
@property (nonatomic, strong) NSString *placeholder;
/**
The color of the placeholder.
The default is `[UIColor lightGrayColor]`.
*/
@property (nonatomic, strong) UIColor *placeholderTextColor;
/**
Returns the drawing rectangle for the text views’s placeholder text.
@param bounds The bounding rectangle of the receiver.
@return The computed drawing rectangle for the placeholder text.
*/
- (CGRect)placeholderRectForBounds:(CGRect)bounds;
@end
SAMTextView.m
//
// SAMTextView.m
// SAMTextView
//
// Created by Sam Soffes on 8/18/10.
// Copyright 2010-2013 Sam Soffes. All rights reserved.
//
#import "SAMTextView.h"
@implementation SAMTextView
#pragma mark - Accessors
@synthesize placeholder = _placeholder;
@synthesize placeholderTextColor = _placeholderTextColor;
- (void)setText:(NSString *)string {
[super setText:string];
[self setNeedsDisplay];
}
- (void)insertText:(NSString *)string {
[super insertText:string];
[self setNeedsDisplay];
}
- (void)setAttributedText:(NSAttributedString *)attributedText {
[super setAttributedText:attributedText];
[self setNeedsDisplay];
}
- (void)setPlaceholder:(NSString *)string {
if ([string isEqual:_placeholder]) {
return;
}
_placeholder = string;
[self setNeedsDisplay];
}
- (void)setContentInset:(UIEdgeInsets)contentInset {
[super setContentInset:contentInset];
[self setNeedsDisplay];
}
- (void)setFont:(UIFont *)font {
[super setFont:font];
[self setNeedsDisplay];
}
- (void)setTextAlignment:(NSTextAlignment)textAlignment {
[super setTextAlignment:textAlignment];
[self setNeedsDisplay];
}
#pragma mark - NSObject
- (void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self name:UITextViewTextDidChangeNotification object:self];
}
#pragma mark - UIView
- (id)initWithCoder:(NSCoder *)aDecoder {
if ((self = [super initWithCoder:aDecoder])) {
[self initialize];
}
return self;
}
- (id)initWithFrame:(CGRect)frame {
if ((self = [super initWithFrame:frame])) {
[self initialize];
}
return self;
}
- (void)drawRect:(CGRect)rect {
[super drawRect:rect];
if (self.text.length == 0 && self.placeholder) {
rect = [self placeholderRectForBounds:self.bounds];
UIFont *font = self.font ? self.font : self.typingAttributes[NSFontAttributeName];
// Draw the text
[self.placeholderTextColor set];
[self.placeholder drawInRect:rect withFont:font lineBreakMode:NSLineBreakByTruncatingTail alignment:self.textAlignment];
}
}
#pragma mark - Placeholder
- (CGRect)placeholderRectForBounds:(CGRect)bounds {
// Inset the rect
CGRect rect = UIEdgeInsetsInsetRect(bounds, self.contentInset);
if (self.typingAttributes) {
NSParagraphStyle *style = self.typingAttributes[NSParagraphStyleAttributeName];
if (style) {
rect.origin.x += style.headIndent;
rect.origin.y += style.firstLineHeadIndent;
}
}
return rect;
}
#pragma mark - Private
- (void)initialize {
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChanged:) name:UITextViewTextDidChangeNotification object:self];
self.placeholderTextColor = [UIColor colorWithWhite:0.702f alpha:1.0f];
}
- (void)textChanged:(NSNotification *)notification {
[self setNeedsDisplay];
}
@end
它比其他的要简单得多,因为它不使用子视图(或有泄漏)。请随意使用。
更新11/10/11:它现在是文档化的,并支持在接口生成器中使用。
更新11/24/13:指向新的回购。
你能做的是在文本属性中设置文本视图的初始值,并将textColor更改为[UIColor grayColor]或类似的东西。然后,每当文本视图变为可编辑时,清除文本并显示游标,如果文本字段再次为空,则将占位符文本放回。根据需要将颜色更改为[UIColor blackColor]。
它与UITextField中的占位符功能不完全相同,但很接近。
这个帖子已经有了很多答案,但这里是我更喜欢的版本。
它扩展了现有的UITextView类,因此很容易重用,并且它不拦截像textViewDidChange这样的事件(这可能会破坏用户的代码,如果他们已经在其他地方拦截了这些事件)。
使用我的代码(如下所示),你可以很容易地添加一个占位符到任何你的UITextViews像这样:
self.textViewComments.placeholder = @"(Enter some comments here.)";
当你设置这个新的占位符值时,它会悄悄地在你的UITextView上添加一个UILabel,然后在必要时隐藏/显示它:
好的,要做这些改变,添加一个包含以下代码的"UITextViewHelper.h"文件:
// UITextViewHelper.h
// Created by Michael Gledhill on 13/02/15.
#import <Foundation/Foundation.h>
@interface UITextView (UITextViewHelper)
@property (nonatomic, strong) NSString* placeholder;
@property (nonatomic, strong) UILabel* placeholderLabel;
@property (nonatomic, strong) NSString* textValue;
-(void)checkIfNeedToDisplayPlaceholder;
@end
…和一个UITextViewHelper。M文件包含:
// UITextViewHelper.m
// Created by Michael Gledhill on 13/02/15.
//
// This UITextView category allows us to easily display a PlaceHolder string in our UITextView.
// The downside is that, your code needs to set the "textValue" rather than the "text" value to safely set the UITextView's text.
//
#import "UITextViewHelper.h"
#import <objc/runtime.h>
@implementation UITextView (UITextViewHelper)
#define UI_PLACEHOLDER_TEXT_COLOR [UIColor colorWithRed:170.0/255.0 green:170.0/255.0 blue:170.0/255.0 alpha:1.0]
@dynamic placeholder;
@dynamic placeholderLabel;
@dynamic textValue;
-(void)setTextValue:(NSString *)textValue
{
// Change the text of our UITextView, and check whether we need to display the placeholder.
self.text = textValue;
[self checkIfNeedToDisplayPlaceholder];
}
-(NSString*)textValue
{
return self.text;
}
-(void)checkIfNeedToDisplayPlaceholder
{
// If our UITextView is empty, display our Placeholder label (if we have one)
if (self.placeholderLabel == nil)
return;
self.placeholderLabel.hidden = (![self.text isEqualToString:@""]);
}
-(void)onTap
{
// When the user taps in our UITextView, we'll see if we need to remove the placeholder text.
[self checkIfNeedToDisplayPlaceholder];
// Make the onscreen keyboard appear.
[self becomeFirstResponder];
}
-(void)keyPressed:(NSNotification*)notification
{
// The user has just typed a character in our UITextView (or pressed the delete key).
// Do we need to display our Placeholder label ?
[self checkIfNeedToDisplayPlaceholder];
}
#pragma mark - Add a "placeHolder" string to the UITextView class
NSString const *kKeyPlaceHolder = @"kKeyPlaceHolder";
-(void)setPlaceholder:(NSString *)_placeholder
{
// Sets our "placeholder" text string, creates a new UILabel to contain it, and modifies our UITextView to cope with
// showing/hiding the UILabel when needed.
objc_setAssociatedObject(self, &kKeyPlaceHolder, (id)_placeholder, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
self.placeholderLabel = [[UILabel alloc] initWithFrame:self.frame];
self.placeholderLabel.numberOfLines = 1;
self.placeholderLabel.text = _placeholder;
self.placeholderLabel.textColor = UI_PLACEHOLDER_TEXT_COLOR;
self.placeholderLabel.backgroundColor = [UIColor clearColor];
self.placeholderLabel.userInteractionEnabled = true;
self.placeholderLabel.font = self.font;
[self addSubview:self.placeholderLabel];
[self.placeholderLabel sizeToFit];
// Whenever the user taps within the UITextView, we'll give the textview the focus, and hide the placeholder if necessary.
[self addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(onTap)]];
// Whenever the user types something in the UITextView, we'll see if we need to hide/show the placeholder label.
[[NSNotificationCenter defaultCenter] addObserver:self selector: @selector(keyPressed:) name:UITextViewTextDidChangeNotification object:nil];
[self checkIfNeedToDisplayPlaceholder];
}
-(NSString*)placeholder
{
// Returns our "placeholder" text string
return objc_getAssociatedObject(self, &kKeyPlaceHolder);
}
#pragma mark - Add a "UILabel" to this UITextView class
NSString const *kKeyLabel = @"kKeyLabel";
-(void)setPlaceholderLabel:(UILabel *)placeholderLabel
{
// Stores our new UILabel (which contains our placeholder string)
objc_setAssociatedObject(self, &kKeyLabel, (id)placeholderLabel, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
[[NSNotificationCenter defaultCenter] addObserver:self selector: @selector(keyPressed:) name:UITextViewTextDidChangeNotification object:nil];
[self checkIfNeedToDisplayPlaceholder];
}
-(UILabel*)placeholderLabel
{
// Returns our new UILabel
return objc_getAssociatedObject(self, &kKeyLabel);
}
@end
是的,它有很多代码,但是一旦你把它添加到你的项目中,并包含了.h文件……
#import "UITextViewHelper.h"
...你可以很容易地在UITextViews中使用占位符。
不过有一个问题。
如果你这样做:
self.textViewComments.placeholder = @"(Enter some comments here.)";
self.textViewComments.text = @"Ooooh, hello there";
...占位符将出现在文本的顶部。设置文本值时,不会调用任何常规通知,因此我不知道如何调用我的函数来决定是否显示/隐藏占位符。
解决方案是设置textValue而不是text:
self.textViewComments.placeholder = @"(Enter some comments here.)";
self.textViewComments.textValue = @"Ooooh, hello there";
或者,您可以设置文本值,然后调用checkIfNeedToDisplayPlaceholder。
self.textViewComments.text = @"Ooooh, hello there";
[self.textViewComments checkIfNeedToDisplayPlaceholder];
我喜欢这样的解决方案,因为它们“填补了”苹果提供给我们的东西和我们(作为开发者)在应用程序中实际需要的东西之间的空白。只需编写一次此代码,将其添加到“helper”.m/.h文件库中,随着时间的推移,SDK实际上开始变得不那么令人沮丧。
(我写了一个类似的帮助添加一个“清除”按钮到我的UITextViews,另一个烦人的东西存在于UITextField但不在UITextView…)
在swift 5。工作很好。
class BaseTextView: UITextView {
// MARK: - Views
private var placeholderLabel: UIlabel!
// MARK: - Init
override init(frame: CGRect, textContainer: NSTextContainer?) {
super.init(frame: frame, textContainer: textContainer)
setupUI()
startupSetup()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setupUI()
startupSetup()
}
deinit {
NotificationCenter.default.removeObserver(self)
}
}
// MARK: - Setup UI
private extension BaseTextView {
func setupUI() {
addPlaceholderLabel()
textColor = .textColor
}
func addPlaceholderLabel() {
placeholderLabel = BaseLabel(frame: .zero)
placeholderLabel.translatesAutoresizingMaskIntoConstraints = false
insertSubview(placeholderLabel, at: 0)
placeholderLabel.alpha = 0
placeholderLabel.numberOfLines = 0
placeholderLabel.backgroundColor = .clear
placeholderLabel.textColor = .lightTextColor
placeholderLabel.lineBreakMode = .byWordWrapping
placeholderLabel.isUserInteractionEnabled = false
placeholderLabel.font = UIFont.openSansSemibold.withSize(12)
placeholderLabel.topAnchor.constraint(equalTo: topAnchor, constant: 8).isActive = true
placeholderLabel.leftAnchor.constraint(equalTo: leftAnchor, constant: 5).isActive = true
placeholderLabel.rightAnchor.constraint(lessThanOrEqualTo: rightAnchor, constant: -8).isActive = true
placeholderLabel.bottomAnchor.constraint(lessThanOrEqualTo: bottomAnchor, constant: -8).isActive = true
}
}
// MARK: - Startup
private extension BaseTextView {
func startupSetup() {
addObservers()
textChanged(nil)
font = UIFont.openSansSemibold.withSize(12)
}
func addObservers() {
NotificationCenter.default.addObserver(self, selector: #selector(textChanged(_:)), name: UITextView.textDidChangeNotification, object: nil)
}
}
// MARK: - Actions
private extension BaseTextView {
@objc func textChanged(_ sender: Notification?) {
UIView.animate(withDuration: 0.2) {
self.placeholderLabel.alpha = self.text.count == 0 ? 1 : 0
}
}
}
// MARK: - Public methods
extension BaseTextView {
public func setPlaceholder(_ placeholder: String) {
placeholderLabel.text = placeholder
}
}
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。