UITextView设置placeholder

下面是我的代码，可以直接拿来用

#import <UIKit/UIKit.h>

@interface CustomTextView : UITextView
@property(nonatomic,strong)NSString *placeholder;
@end

#import "CustomTextView.h"

@interface CustomTextView ()
@property(nonatomic,strong)UILabel *placeLab;
@end

@implementation CustomTextView

-(instancetype)initWithFrame:(CGRect)frame{
    self = [super initWithFrame:frame];
    if(self){
        
        self.placeLab  = [UILabel new];
        self.placeLab.textColor = [ImageService colorWithHexString:GRAY_COLOR];
        [self addSubview:self.placeLab];
        self.placeLab.textAlignment = NSTextAlignmentRight;
        [self.placeLab mas_makeConstraints:^(MASConstraintMaker *make) {
            make.top.left.offset(5);
            make.width.equalTo(self.mas_width).offset(-10);
        }];
        [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(beginChange) name:UITextViewTextDidBeginEditingNotification object:self];
        [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(didChange) name:UITextViewTextDidChangeNotification object:self];
        
    }
    return self;
}
-(void)setFont:(UIFont *)font {
    [super setFont:font];
    self.placeLab.font = font;
}
-(void)setTextAlignment:(NSTextAlignment)textAlignment{
    [super setTextAlignment:textAlignment];
    self.placeLab.textAlignment = textAlignment;
}


-(void)setPlaceholder:(NSString *)placeholder{
    _placeholder = placeholder;
    self.placeLab.text = placeholder;
}

-(void)beginChange{
    if([self.text isEqualToString:@""]){
        self.placeLab.hidden = NO;
    }else{
        self.placeLab.hidden = YES;
    }
}
-(void)didChange{
    if([self.text isEqualToString:@""]){
        self.placeLab.hidden = NO;
    }else{
        self.placeLab.hidden = YES;
    }
}
-(void)setText:(NSString *)text{
    [super setText:text];
    [self beginChange];
}


@end

-(void)dealloc{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextViewTextDidBeginEditingNotification object:self];
     [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextViewTextDidChangeNotification object:self];
}