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
基于这里已经给出的一些很好的建议,我能够将以下轻量级的、与接口生成器兼容的UITextView子类组合在一起,它是:
包括可配置的占位符文本,样式就像UITextField一样。 不需要任何额外的子视图或约束。 不需要来自ViewController的任何委托或其他行为。 不需要任何通知。 保持该文本与查看字段的文本属性的任何外部类完全分离。
欢迎提出改进建议。
编辑1:更新为重置占位符格式,如果实际文本以编程方式设置。
编辑2:现在可以以编程方式检索占位符文本颜色。
斯威夫特v5:
import UIKit
@IBDesignable class TextViewWithPlaceholder: UITextView {
override var text: String! { // Ensures that the placeholder text is never returned as the field's text
get {
if showingPlaceholder {
return "" // When showing the placeholder, there's no real text to return
} else { return super.text }
}
set {
if showingPlaceholder {
removePlaceholderFormatting() // If the placeholder text is what's being changed, it's no longer the placeholder
}
super.text = newValue
}
}
@IBInspectable var placeholderText: String = ""
@IBInspectable var placeholderTextColor: UIColor = .placeholderText
private var showingPlaceholder: Bool = true // Keeps track of whether the field is currently showing a placeholder
override func didMoveToWindow() {
super.didMoveToWindow()
if text.isEmpty {
showPlaceholderText() // Load up the placeholder text when first appearing, but not if coming back to a view where text was already entered
}
}
override public func becomeFirstResponder() -> Bool {
// If the current text is the placeholder, remove it
if showingPlaceholder {
text = nil
removePlaceholderFormatting()
}
return super.becomeFirstResponder()
}
override public func resignFirstResponder() -> Bool {
// If there's no text, put the placeholder back
if text.isEmpty {
showPlaceholderText()
}
return super.resignFirstResponder()
}
private func showPlaceholderText() {
text = placeholderText
showingPlaceholder = true
textColor = placeholderTextColor
}
private func removePlaceholderFormatting() {
showingPlaceholder = false
textColor = nil // Put the text back to the default, unmodified color
}
}
其他回答
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];
}
- (void)textViewDidChange:(UITextView *)textView
{
placeholderLabel.hidden = YES;
}
在textview上放一个标签。
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…)
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。
我修改了Sam Soffes的实现以适应iOS7:
- (void)drawRect:(CGRect)rect
{
[super drawRect:rect];
if (_shouldDrawPlaceholder)
{
UIEdgeInsets insets = self.textContainerInset;
CGRect placeholderRect = CGRectMake(
insets.left + self.textContainer.lineFragmentPadding,
insets.top,
self.frame.size.width - insets.left - insets.right,
self.frame.size.height - insets.top - insets.bottom);
[_placeholderText drawWithRect:placeholderRect
options:NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingTruncatesLastVisibleLine
attributes:self.placeholderAttributes
context:nil];
}
}
- (NSDictionary *)placeholderAttributes
{
if (_placeholderAttributes == nil)
{
_placeholderAttributes = @
{
NSFontAttributeName : self.font,
NSForegroundColorAttributeName : self.placeholderColor
};
}
return _placeholderAttributes;
}
记住在可能改变字体和其他可能影响它们的东西的方法中设置_placeholderattributes = nil。如果没有问题的话,您可能还想跳过属性字典的“惰性”创建。
编辑:
如果你想让占位符在自动布局动画之后看起来更好,记得在setBounds的重写版本中调用setNeedsDisplay。