UITextView添加一个placeholder功能

控件UITextField有个placeholder属性，UITextField和UITextView使用方法基本类似，有两个小区别：1.UITextField单行输入，而UITextView可以多行输入。2.UITextField有placeholder属性，而UITextView没有。至于两者的代理方法，原理基本差不多，只是方法名略有差异。

实现该功能有两种方式 一种是 ①使用通知 显示隐藏遮盖物

②使用代理 给文本框重新赋值

1.在创建textView的时候，赋值其文本属性

即textView.text = @"想说的话"；

2.在开始编辑和结束编辑的代理方法中进行判断

 //
 //  ViewController.m
 //  绘制TextView
 //
 //  Created by zjj on 15/7/1.
 //  Copyright (c) 2015年 zjj. All rights reserved.
 //

 #import "ViewController.h"
 #import "DJTextView.h"
 #import "DJplaceHolderTextView.h"
 @interface ViewController () <UITextViewDelegate>
 @property (nonatomic,strong)DJplaceHolderTextView *placeHolderText;
 @end

 @implementation ViewController

 - (void)viewDidLoad {
     [super viewDidLoad];
     UITextField *text1 = [[UITextField alloc]initWithFrame:CGRectMake(, , , )];
     text1.backgroundColor = [UIColor grayColor];
     text1.placeholder = @"请输入账号";
     text1.clearButtonMode = UITextFieldViewModeWhileEditing;
     [self.view addSubview:text1];

     // 做法① 使用通知 用一个UIlabel遮盖再UItextView上面 根据输入文字是否为0来隐藏显示遮盖物 文字提示
     DJTextView *text = [[DJTextView alloc]initWithFrame:CGRectMake(, , , )];
     text.backgroundColor = [UIColor grayColor];
     text.placeholder = @"请输入账号";
     text.placeholderColor = [UIColor whiteColor];
     [self.view addSubview:text];

     // 做法② 使用UITextViewDelegate代理 开始编辑和结束编辑事件重新赋值文本属性
     _placeHolderText = [[DJplaceHolderTextView alloc]initWithFrame:CGRectMake(, , , )];
     _placeHolderText.backgroundColor = [UIColor grayColor];
     _placeHolderText.placeholder = @"请输入账号";
     _placeHolderText.text = _placeHolderText.placeholder;
     _placeHolderText.delegate = self;
     [self.view addSubview:_placeHolderText];
 }
 /**
  *  开始编辑事件
  */
 - (void)textViewDidBeginEditing:(UITextView *)textView
 {
 //  NSLog(@"textViewDidBeginEditing%@ - %ld - %@",textView.text,textView.text.length,self.placeHolderText.placeholder);
     if ([textView.text isEqualToString:self.placeHolderText.placeholder]) {
         textView.text = @"";
     }
 }
 /**
  *  结束编辑事件
  */
 - (void)textViewDidEndEditing:(UITextView *)textView
 {
 //    NSLog(@"textViewDidBeginEditing%@ - %ld - %@",textView.text,textView.text.length,self.placeHolderText.placeholder);
     if (textView.text.length < ) {
         textView.text = self.placeHolderText.placeholder;
     }
 }

 @end

 // 做法② 使用UITextViewDelegate代理 开始编辑和结束编辑事件重新赋值文本属性

 //
 //  DJplaceHolderTextView.h
 //  绘制TextView
 //
 //  Created by zjj on 15/7/2.
 //  Copyright (c) 2015年 zjj. All rights reserved.
 //

 #import <UIKit/UIKit.h>

 @interface DJplaceHolderTextView : UITextView
 /**
  *  placehold 用户输入前文本提示
  */
 @property (nonatomic,copy) NSString *placeholder;
 @end

// 做法① 使用通知 用一个UIlabel遮盖再UItextView上面 根据输入文字是否为0来隐藏显示遮盖物 文字提示

 //
 //  DJTextView.h
 //  绘制TextView
 //
 //  Created by zjj on 15/7/1.
 //  Copyright (c) 2015年 zjj. All rights reserved.
 //

 #import <UIKit/UIKit.h>
 /**
  *  UITextView 实现 placeholder 及隐藏键盘
  */
 @interface DJTextView : UITextView
 /**
  *  placehold 用户输入前文本提示
  */
 @property (nonatomic,copy) NSString *placeholder;
 /**
  *  placeholder 文字颜色
  */
 @property (nonatomic,strong)UIColor *placeholderColor;
 /**
  *  placeholder 提示label
  */
 @property (nonatomic,strong)UILabel *placeholderLabel;
 /**
  *  文本改变事件
  */
 -(void)textChanged:(NSNotification*)notification;
 @end

 //
 //  DJTextView.m
 //  绘制TextView
 //
 //  Created by zjj on 15/7/1.
 //  Copyright (c) 2015年 zjj. All rights reserved.
 //

 #import "DJTextView.h"

 @implementation DJTextView

 //-(void)setPlaceholder:(NSString *)placeholder
 //{
 //    _placeholder = placeholder;
 //
 //    [self setNeedsDisplay];
 //}
 //
 //- (void)drawRect:(CGRect)rect
 //{
 //
 //    [self.placeholder drawInRect:rect withAttributes:nil];
 //}

 - (void)dealloc

 {

     [[NSNotificationCenter defaultCenter] removeObserver:self];

 //    placeHolderLabel = nil;
 //
 //    [placeholderColor release]; placeholderColor = nil;
 //
 //    [placeholder release]; placeholder = nil;

 //    [super dealloc];

 }

 - (void)awakeFromNib

 {

     [super awakeFromNib];

     [self setPlaceholder:@""];

     [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] == )

     {

         return;

     }

     if([[self text] length] == )

     {

         [[self viewWithTag:] setAlpha:];

     }

     else

     {

         [[self viewWithTag:] setAlpha:];

     }

 }

 - (void)setText:(NSString *)text {

     [super setText:text];

     [self textChanged:nil];

 }

 - (void)drawRect:(CGRect)rect

 {

     if( [[self placeholder] length] >  )

     {

         if ( self.placeholderLabel == nil )

         {

             self.placeholderLabel = [[UILabel alloc] initWithFrame:CGRectMake(,,self.bounds.size.width - ,)];
             self.placeholderLabel.lineBreakMode = UILineBreakModeWordWrap;//过时的
             self.placeholderLabel.numberOfLines = ;

             self.placeholderLabel.font = self.font;

             self.placeholderLabel.backgroundColor = [UIColor clearColor];

             self.placeholderLabel.textColor = self.placeholderColor;

             self.placeholderLabel.alpha = ;

             self.placeholderLabel.tag = ;

             [self addSubview:self.placeholderLabel];

         }

         self.placeholderLabel.text = self.placeholder;

         [self.placeholderLabel sizeToFit];

         [self sendSubviewToBack:self.placeholderLabel];

     }

     if( [[self text] length] ==  && [[self placeholder] length] >  )

     {

         [[self viewWithTag:] setAlpha:];

     }

     [super drawRect:rect];

 }
 ////隐藏键盘，实现UITextViewDelegate
 //
 //-(BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString*)text
 //
 //{
 //
 //    if ([text isEqualToString:@"\n"]) {
 //
 //        [textView resignFirstResponder];
 //
 //        return NO;
 //
 //    }
 //
 //    return YES;
 //
 //}

 @end

推荐使用第一种