//.h文件  
  
#import <UIKit/UIKit.h>  
  
@interface XYLPlaceHodlerTextView : UITextView  
  
/**placeholder占位文字*/  
@property (nonatomic, copy) NSString *placeholder;  
/**placeholderColor占位文字颜色*/  
@property (nonatomic, strong) UIColor *placeholderColor;  
@end  

// .m文件  
#import "XYLPlaceHodlerTextView.h"  
@interface XYLPlaceHodlerTextView()  
/**UILabel*/  
@property (nonatomic, strong) UILabel *placeholderLabel;  
@end  
@implementation XYLPlaceHodlerTextView  
/** 
 *  懒加载属性，并设置属性的值 
 */  
-(UILabel *)placeholderLabel  
{  
  if (!_placeholderLabel) {  
    UILabel *label = [[UILabel alloc]init];  
    label.font = [UIFont systemFontOfSize:14];  
    label.textColor = [UIColor grayColor];  
    label.numberOfLines = 0;  
    _placeholderLabel = label;  
  }  
  return _placeholderLabel;  
}  
/** 
 *  设置自己的属性 
 */  
-(instancetype)initWithFrame:(CGRect)frame  
{  
  if (self = [super initWithFrame:frame]) {  
    self.alwaysBounceVertical = YES;  
    self.textColor = [UIColor blackColor];  
    [XYLNotificationCenter addObserver:self selector:@selector(texting) name:UITextViewTextDidChangeNotification object:self];  
  }  
  return self;  
}  
/** 
 *  监听有文字输入 
 */  
-(void)texting  
{  
  [self setPlaceholderTextShow];  
}  
/** 
 *  设置占位文字的显示 
 */  
-(void)setPlaceholderTextShow  
{  
  self.placeholderLabel.hidden = self.hasText;  
}  
-(void)layoutSubviews  
{  
  [super layoutSubviews];  
  self.placeholderLabel.x = 4;  
  self.placeholderLabel.y = 8;  
  self.placeholderLabel.width = self.width - 22 * self.placeholderLabel.x;  
  [self.placeholderLabel sizeToFit];//这一步很重要，不能遗忘  
}  
-(void)setPlaceholder:(NSString *)placeholder  
{  
//  _placeholder = placeholder;//此句的意义何在？  
  self.placeholderLabel.text = placeholder;  
  [self setNeedsLayout];  
}  
-(void)setPlaceholderColor:(UIColor *)placeholderColor  
{  
  self.placeholderLabel.textColor = placeholderColor;  
  [self setNeedsLayout];  
}  
-(void)setFont:(UIFont *)font  
{  
  [super setFont:font];  
  self.placeholderLabel.font = font;  
  [self setNeedsLayout];  
}  
-(void)setText:(NSString *)text  
{  
  [super setText:text];  
  [self setPlaceholderTextShow];  
}  
-(void)setAttributedText:(NSAttributedString *)attributedText  
{  
  [super setAttributedText:attributedText];  
  [self setPlaceholderTextShow];  
}  
@end  

注意点：

界面显示步骤是先调用layoutSubviews将所有子控件的位置frame设计好，然后再调用drawRect方法画上去。

layoutSubviews的调用时机：

init时不会被调用

将要真正显示的会调用

frame发现改变时智能调用

滚动、旋转、remove等等时

这些时机都是和frame相关的，也是唯一能更新子视图的最好时机