iOS开发-UITextView实现PlaceHolder的方式

之前开发遇到过UITextField中加入一个PlaceHolder的问题，直接设置一下即可，不过这次是需要在UITextView中实现一个PlaceHolder，跟之前有点不同。在网上参考了各位前辈的解决方案，大概有两种方式，第一种方式很猥琐，就是直接给UITextView的text赋值，比如说默认提示是"博客园FlyElephant"，在textViewDidChange中判断是不是“博客园FlyElephant”，如果是就清空，如果不是就继续提示，弊端就是用户输入的内容不能和你的默认提示一样，第二种方式需要加入一个UILabel，同样在textViewDidChange中进行判断，一般都是这么实现，不过有的都是创建textView中的时候创建UILabel，这样做无可厚非，不过最好还是抽象出来。继承UITextView扩展一下，新建一个FEPlaceHolderTextView：

头文件:

//
//  FEPlaceHolderTextView.h
//  MyTextViewDemo
//http://www.cnblogs.com/xiaofeixiang
//  Created by keso on 15/5/17.
//  Copyright (c) 2015年 keso. All rights reserved.
//
 
#import <UIKit/UIKit.h>
 
@interface FEPlaceHolderTextView : UITextView
 
@property (nonatomic, retain) NSString *placeholder;
@property (nonatomic, retain) UIColor *placeholderColor;
 
-(void)textChanged:(NSNotification*)notification;
 
@end

　实现文件:

//
//  FEPlaceHolderTextView.m
//  MyTextViewDemo
//http://www.cnblogs.com/xiaofeixiang
//  Created by keso on 15/5/17.
//  Copyright (c) 2015年 keso. All rights reserved.
//
 
#import "FEPlaceHolderTextView.h"
 
@interface FEPlaceHolderTextView ()
 
@property (nonatomic, retain) UILabel *placeHolderLabel;
 
@end
 
@implementation FEPlaceHolderTextView
 
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.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

　调用:

    self.textView=[[FEPlaceHolderTextView alloc]initWithFrame:CGRectMake(10, 30, CGRectGetWidth(self.view.frame)-20, 200)];
    self.textView.placeholder=@"博客园FlyElephant\n博客地址:http://www.cnblogs.com/xiaofeixiang";
    self.textView.layer.borderColor=[UIColor lightGrayColor].CGColor;
    self.textView.layer.borderWidth=1.0;
    self.textView.scrollEnabled = YES;
    self.textView.autoresizingMask =
    UIViewAutoresizingFlexibleHeight; //自适应高度
    self.textView.returnKeyType = UIReturnKeyDefault; //返回键的类型
 
    self.textView.keyboardType = UIKeyboardTypeDefault; //键盘类型
    [self.view addSubview:self.textView];

效果: