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
下面是“SAMTextView”ObjC代码的Swift端口,作为对这个问题的第一批回答之一。我在iOS 8上进行了测试。我调整了一些东西,包括占位符文本的位置的边界偏移,因为原来的位置太高,太右了(在那个帖子的一个评论中使用了建议)。
我知道有很多简单的解决方案,但我喜欢子类化UITextView的方法,因为它是可重用的,而且我不必在使用它的机制时使类变得混乱。
斯威夫特2.2:
import UIKit
class PlaceholderTextView: UITextView {
@IBInspectable var placeholderColor: UIColor = UIColor.lightGrayColor()
@IBInspectable var placeholderText: String = ""
override var font: UIFont? {
didSet {
setNeedsDisplay()
}
}
override var contentInset: UIEdgeInsets {
didSet {
setNeedsDisplay()
}
}
override var textAlignment: NSTextAlignment {
didSet {
setNeedsDisplay()
}
}
override var text: String? {
didSet {
setNeedsDisplay()
}
}
override var attributedText: NSAttributedString? {
didSet {
setNeedsDisplay()
}
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setUp()
}
override init(frame: CGRect, textContainer: NSTextContainer?) {
super.init(frame: frame, textContainer: textContainer)
}
private func setUp() {
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(PlaceholderTextView.textChanged(_:)),
name: UITextViewTextDidChangeNotification, object: self)
}
func textChanged(notification: NSNotification) {
setNeedsDisplay()
}
func placeholderRectForBounds(bounds: CGRect) -> CGRect {
var x = contentInset.left + 4.0
var y = contentInset.top + 9.0
let w = frame.size.width - contentInset.left - contentInset.right - 16.0
let h = frame.size.height - contentInset.top - contentInset.bottom - 16.0
if let style = self.typingAttributes[NSParagraphStyleAttributeName] as? NSParagraphStyle {
x += style.headIndent
y += style.firstLineHeadIndent
}
return CGRect(x: x, y: y, width: w, height: h)
}
override func drawRect(rect: CGRect) {
if text!.isEmpty && !placeholderText.isEmpty {
let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.alignment = textAlignment
let attributes: [ String: AnyObject ] = [
NSFontAttributeName : font!,
NSForegroundColorAttributeName : placeholderColor,
NSParagraphStyleAttributeName : paragraphStyle]
placeholderText.drawInRect(placeholderRectForBounds(bounds), withAttributes: attributes)
}
super.drawRect(rect)
}
}
斯威夫特4.2:
import UIKit
class PlaceholderTextView: UITextView {
@IBInspectable var placeholderColor: UIColor = UIColor.lightGray
@IBInspectable var placeholderText: String = ""
override var font: UIFont? {
didSet {
setNeedsDisplay()
}
}
override var contentInset: UIEdgeInsets {
didSet {
setNeedsDisplay()
}
}
override var textAlignment: NSTextAlignment {
didSet {
setNeedsDisplay()
}
}
override var text: String? {
didSet {
setNeedsDisplay()
}
}
override var attributedText: NSAttributedString? {
didSet {
setNeedsDisplay()
}
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setUp()
}
override init(frame: CGRect, textContainer: NSTextContainer?) {
super.init(frame: frame, textContainer: textContainer)
}
private func setUp() {
NotificationCenter.default.addObserver(self,
selector: #selector(self.textChanged(notification:)),
name: Notification.Name("UITextViewTextDidChangeNotification"),
object: nil)
}
@objc func textChanged(notification: NSNotification) {
setNeedsDisplay()
}
func placeholderRectForBounds(bounds: CGRect) -> CGRect {
var x = contentInset.left + 4.0
var y = contentInset.top + 9.0
let w = frame.size.width - contentInset.left - contentInset.right - 16.0
let h = frame.size.height - contentInset.top - contentInset.bottom - 16.0
if let style = self.typingAttributes[NSAttributedString.Key.paragraphStyle] as? NSParagraphStyle {
x += style.headIndent
y += style.firstLineHeadIndent
}
return CGRect(x: x, y: y, width: w, height: h)
}
override func draw(_ rect: CGRect) {
if text!.isEmpty && !placeholderText.isEmpty {
let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.alignment = textAlignment
let attributes: [NSAttributedString.Key: Any] = [
NSAttributedString.Key(rawValue: NSAttributedString.Key.font.rawValue) : font!,
NSAttributedString.Key(rawValue: NSAttributedString.Key.foregroundColor.rawValue) : placeholderColor,
NSAttributedString.Key(rawValue: NSAttributedString.Key.paragraphStyle.rawValue) : paragraphStyle]
placeholderText.draw(in: placeholderRectForBounds(bounds: bounds), withAttributes: attributes)
}
super.draw(rect)
}
}
其他回答
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
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。
这是我的版本的UITextView与占位符支持。斯威夫特4.2 https://gist.github.com/hlung/c5dda3a0c2087e5ae6c1fce8822c4713
一个支持占位符文本的UITextView子类。它使用另一个 UILabel显示占位符,当文本为空时显示。
- (void)viewDidLoad {
[super viewDidLoad];
self.textViewEmpty = YES;
// Text view
self.textView = [[UITextView alloc] init];
self.textView.translatesAutoresizingMaskIntoConstraints = NO; // For AutoLayout
self.textView.delegate = self;
self.textView.textColor = [UIColor grayColor];
self.textView.text = @"Placeholder";
// Add subview and constraints
}
#pragma mark - UITextView
- (BOOL)textViewShouldBeginEditing:(UITextView *)textView {
if (self.isTextViewEmpty) {
textView.textColor = [UIColor blackColor];
textView.text = @"";
}
return YES;
}
- (void)textViewDidChange:(UITextView *)textView {
if (textView.text.length > 0) {
self.textViewEmpty = NO;
} else {
self.textViewEmpty = YES;
}
}
- (BOOL)textViewShouldEndEditing:(UITextView *)textView {
if (self.isTextViewEmpty) {
textView.textColor = [UIColor lightGrayColor];
textView.text = placeholderText;
}
return YES;
}
如果有人需要Swift的解决方案:
添加UITextViewDelegate到类中
var placeHolderText = "Placeholder Text..."
override func viewDidLoad() {
super.viewDidLoad()
textView.delegate = self
}
func textViewShouldBeginEditing(textView: UITextView) -> Bool {
self.textView.textColor = .black
if(self.textView.text == placeHolderText) {
self.textView.text = ""
}
return true
}
func textViewDidEndEditing(textView: UITextView) {
if(textView.text == "") {
self.textView.text = placeHolderText
self.textView.textColor = .lightGray
}
}
override func viewWillAppear(animated: Bool) {
if(currentQuestion.answerDisplayValue == "") {
self.textView.text = placeHolderText
self.textView.textColor = .lightGray
} else {
self.textView.text = "xxx" // load default text / or stored
self.textView.textColor = .black
}
}