自定义的te'x't'vi'e'w带有占位文字

//
//  STPlaceHolderTextView.h
//  yunxinDemo
//
//  Created by 刘小二 on 16/7/13.
//  Copyright © 2016年 刘小二. All rights reserved.
//

#import 

@interface STPlaceHolderTextView : UITextView

/** 占位文字 */
@property (nonatomic, strong) NSString *placeholder;

/** 占位文字字体大小 */
@property (nonatomic, assign) CGFloat placeholderFont;

/** 占位文字颜色 */
@property (nonatomic, strong) UIColor *placeholderColor;

@end

```objc
//
//  STPlaceHolderTextView.m
//  yunxinDemo
//
//  Created by 刘小二 on 16/7/13.
//  Copyright © 2016年 刘小二. All rights reserved.
//

#import "STPlaceHolderTextView.h"

static CGFloat const STplaceholderDefaultFont = 13.0; // 默认占位文字大小
#define STplaceholderDefaultColor [UIColor grayColor] // 默认占位文字颜色
static CGFloat const STplaceholderDefaultInsets = 5.0; // 默认占位文字的间隙

@implementation STPlaceHolderTextView

- (void)setPlaceholder:(NSString *)placeholder {

   if ([placeholder isEqualToString:_placeholder]) {
       
       return;
   }
   _placeholder = placeholder;
   
   [self setNeedsDisplay];
}

- (void)setPlaceholderFont:(CGFloat)placeholderFont {

   if (placeholderFont == _placeholderFont) {
       
       return;
   }
   _placeholderFont = placeholderFont;
   
   [self setNeedsDisplay];

   
}

- (void)setPlaceholderColor:(UIColor *)placeholderColor {

   if (placeholderColor == _placeholderColor) {
       
       return;
   }
   
   _placeholderColor = placeholderColor;
   
   [self setNeedsDisplay];
}


- (instancetype)initWithCoder:(NSCoder *)coder
{
   self = [super initWithCoder:coder];
   if (self) {
       
       [self setNeedsDisplay];
       
       [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textViewDidChange:) name: UITextViewTextDidChangeNotification    object:nil];
   }
   return self;
}

- (void)setText:(NSString *)text {
   [super setText:text];
   [self setNeedsDisplay];
}

- (void)setAttributedText:(NSAttributedString *)attributedText {
   [super setAttributedText:attributedText];
   [self setNeedsDisplay];
}



- (void)setFrame:(CGRect)frame{
   if (self.frame.size.width != frame.size.width) {
       [self setNeedsDisplay];
   }
   [super setFrame:frame];
}


- (instancetype)initWithFrame:(CGRect)frame
{
   self = [super initWithFrame:frame];
   if (self) {
       
       
       self.placeholderFont = STplaceholderDefaultFont;
       self.placeholderColor = STplaceholderDefaultColor;
       
       [self setNeedsDisplay];
       
       [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textViewDidChange:) name: UITextViewTextDidChangeNotification object:self];
       
   }
   return self;
}

- (void)textViewDidChange:(NSNotification*)object {

   [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect {
   
   [super drawRect:rect];

   if (self.text.length == 0 && self.placeholder) {
       
   
       NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
       paragraphStyle.lineBreakMode = NSLineBreakByTruncatingTail;
       paragraphStyle.alignment = self.textAlignment;
   
       
   
   [self.placeholder drawInRect:CGRectMake(STplaceholderDefaultInsets, STplaceholderDefaultInsets, rect.size.width, rect.size.height) withAttributes:
                     @{
                       NSFontAttributeName:[UIFont systemFontOfSize:self.placeholderFont == STplaceholderDefaultFont ? STplaceholderDefaultFont: self.placeholderFont],
                       
                       NSForegroundColorAttributeName:self.placeholderColor == STplaceholderDefaultColor ? STplaceholderDefaultColor:self.placeholderColor,
                       
                       NSParagraphStyleAttributeName:paragraphStyle
                       
                       }];
   }
}


- (void)dealloc {

   _placeholder = nil;
   [[NSNotificationCenter defaultCenter]removeObserver:self name:UITextViewTextDidChangeNotification object:self];
}
@end