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
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];
}
}
其他回答
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。
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];
}
}
简单地创建UITextView的@IBDesignable子类:
@IBDesignable class AttributedTextView: UITextView {
private let placeholderLabel = UILabel()
@IBInspectable var placeholder: String = "" {
didSet {
setupPlaceholderLabelIfNeeded()
textViewDidChange()
}
}
override var text: String! {
didSet {
textViewDidChange()
}
}
//MARK: - Initialization
override func awakeFromNib() {
super.awakeFromNib()
setupPlaceholderLabelIfNeeded()
NotificationCenter.default.addObserver(self, selector: #selector(textViewDidChange), name: .UITextViewTextDidChange, object: nil)
}
//MARK: - Deinitialization
deinit {
NotificationCenter.default.removeObserver(self)
}
//MARK: - Internal
func textViewDidChange() {
placeholderLabel.isHidden = !text.isEmpty
layoutIfNeeded()
}
//MARK: - Private
private func setupPlaceholderLabelIfNeeded() {
placeholderLabel.removeFromSuperview()
placeholderLabel.frame = CGRect(x: 0, y: 8, width: frame.size.width, height: 0)
placeholderLabel.textColor = UIColor.lightGray
placeholderLabel.text = placeholder
placeholderLabel.sizeToFit()
insertSubview(placeholderLabel, at: 0)
}
}
然后在标识检查器中设置占位符:
Jason的答案在iOS7中看起来有点不对劲，通过调整_placeHolderLabel的偏移量来修复它:
- (void)drawRect:(CGRect)rect
{
if( [[self placeholder] length] > 0 )
{
if (_placeHolderLabel == nil )
{
if ([[UIDevice currentDevice].systemVersion floatValue] >= 7)
_placeHolderLabel = [[UILabel alloc] initWithFrame:CGRectMake(4,8,self.bounds.size.width - 8,0)];
else
_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];
}
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。
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