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
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。
其他回答
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
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
}
}
更简单,并且仍然考虑到用户在某些时候输入的一些文本
BOOL placeHolderTextVisible;
在viewDidLoad上,设置它为YES(或DidMoveToSuperview,或awakeFromNib)
然后,在 - (BOOL) textView:(UITextView*)textView shouldBeginEditing
- (BOOL)textViewShouldBeginEditing:(UITextView *)textView;
{
if (placeHolderTextVisible) {
placeHolderTextVisible = NO;
textView.text = @"";
}
return YES;
}
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。
你也可以创建一个新的类TextViewWithPlaceholder作为UITextView的子类。
(这段代码有点粗糙——但我认为它在正确的轨道上。)
@interface TextViewWithPlaceholder : UITextView
{
NSString *placeholderText; // make a property
UIColor *placeholderColor; // make a property
UIColor *normalTextColor; // cache text color here whenever you switch to the placeholderColor
}
- (void) setTextColor: (UIColor*) color
{
normalTextColor = color;
[super setTextColor: color];
}
- (void) updateForTextChange
{
if ([self.text length] == 0)
{
normalTextColor = self.textColor;
self.textColor = placeholderColor;
self.text = placeholderText;
}
else
{
self.textColor = normalTextColor;
}
}
在委托中,添加以下内容:
- (void)textViewDidChange:(UITextView *)textView
{
if ([textView respondsToSelector: @selector(updateForTextChange)])
{
[textView updateForTextChange];
}
}