实现UITextView实现PlaceHolder的方式的方式有两种，这两种方法的核心就是通过通知来添加和去除PlaceHolder；下面来介绍两种方法；个人比较喜欢第一种，看起来更加合理。
方法1：原理是通过通知来改变PlaceHolder，把PlaceHolder看成是一个UILabel，设置UILabel的透明度，来让Placeholder显示与不显示。这种方法对UITextView本身影响较小。学习自Fly_Elephant：《UITextView实现PlaceHolder的方式》这篇文章
.h文件
#import <UIKit/UIKit.h> @interface DLTextView : UITextView @property (nonatomic, retain) NSString *placeholder; @property (nonatomic, retain) UIColor *placeholderColor; - (void)textChanged:(NSNotification*)notification; @end
.m文件
#import "DLTextView.h" @interface DLTextView ()
@property (nonatomic, retain) UILabel *placeHolderLabel; @end @implementation DLTextView CGFloat const UI_PLACEHOLDER_TEXT_CHANGED_ANIMATION_DURATION = 0.25; - (void)dealloc
{
[[NSNotificationCenter defaultCenter] removeObserver:self];
} - (void)awakeFromNib
{
[super awakeFromNib];
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, 10)];
_placeHolderLabel.lineBreakMode = NSLineBreakByWordWrapping;
_placeHolderLabel.numberOfLines = 0;
// _placeHolderLabel.font = self.font;
_placeHolderLabel.font = [UIFont systemFontOfSize:13.0];
_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
第二种方法：原理是通过Placeholder字符串的长度，当textView输入内容时，Placeholder 字符串的长度为nil，当textView不输入内容时，Placeholder显示。
#import <UIKit/UIKit.h> @interface DLTextView : UITextView @property (nonatomic, copy) NSString *placeholder; @end
#import "DLTextView.h" @implementation DLTextView - (instancetype)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
[self setup];
}
return self;
}
- (instancetype)initWithCoder:(NSCoder *)decoder
{
self = [super initWithCoder:decoder];
if (self) {
[self setup]; }
return self;
}
- (void)awakeFromNib
{
// [self setup]; } - (void)setup
{
// NSMutableAttributedString *attributedText = [[NSMutableAttributedString alloc] initWithString:super.text];
// NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
// paragraphStyle.lineSpacing = 10;
//
// [attributedText addAttributes:@{NSParagraphStyleAttributeName : paragraphStyle} range:NSMakeRange(0, super.text.length)];
//
// super.attributedText = attributedText; // 添加通知
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textViewDidBeginEditing:) name:UITextViewTextDidBeginEditingNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textViewDidEndEditing:) name:UITextViewTextDidEndEditingNotification object:nil];
}
- (void)dealloc
{
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
#pragma mark - 开始编辑的消息方法
- (void)textViewDidBeginEditing:(NSNotification *)sender
{
// 开始编辑的时候，父控件的text如果等于placeholder就让什么也不显示
if ([super.text isEqualToString:self.placeholder]) {
super.text = @"";
[super setTextColor:[UIColor blackColor]];
} } - (void)textViewDidEndEditing:(NSNotification *)sender
{
if (super.text.length == 0) {
super.text = self.placeholder;
[super setTextColor:[UIColor grayColor]];
}
}
- (void)setPlaceholder:(NSString *)placeholder
{
_placeholder = placeholder; // 调用通知的方法，让placeholder显示在UI上面
[self textViewDidEndEditing:nil];
}
#pragma mark - 重写父类的text方法
- (NSString *)text
{
if ([super.text isEqualToString:self.placeholder]) { super.text = @"";
} return super.text;
}
@end