iOS给UITextView添加Placeholder

////  LAXTextView.h//  LAXTextViewPlaceHolder////  Created by 刘翱翔 on 2017/1/7.//  Copyright © 2017年 liuaoxiang. All rights reserved.//#import <UIKit/UIKit.h>@interface LAXTextView : UITextView@property(nonatomic, assign) BOOL hasText2;@property(nonatomic,copy) NSString *placeholder;  //文字@property(nonatomic,strong) UIColor *placeholderColor; //文字颜色@end

////  LAXTextView.m//  LAXTextViewplaceholder////  Created by 刘翱翔 on 2017/1/7.//  Copyright © 2017年 liuaoxiang. All rights reserved.//#import "LAXTextView.h"#import "NSObject+KVOCategory.h"@interface LAXTextView ()@property(nonatomic,copy) UIFont *placeholderFont;@property (nonatomic, strong) UILabel * placeholderLabel;@end@implementation LAXTextView#pragma mark - Setters- (UILabel *)placeholderLabel {    if (!_placeholderLabel) {        [self setup];    }    return _placeholderLabel;}- (void)setPlaceholder:(NSString *)placeholder {    if([placeholder isEqualToString:_placeholder]) {        return;    }    _placeholder = placeholder;    self.placeholderLabel.text = placeholder;    [self setNeedsDisplay];    [self notificationAction];}- (void)setPlaceholderColor:(UIColor *)placeholderColor {    if([placeholderColor isEqual:_placeholderColor]) {        return;    }    _placeholderColor = placeholderColor;    self.placeholderLabel.textColor = _placeholderColor;    [self setNeedsDisplay];    [self notificationAction];}#pragma mark - Message text view- (NSUInteger)numberOfLinesOfText {    return [LAXTextView numberOfLinesForMessage:self.text];}+ (NSUInteger)maxCharactersPerLine {    return ([UIDevice currentDevice].userInterfaceIdiom == UIUserInterfaceIdiomPhone) ? 33 : 109;}+ (NSUInteger)numberOfLinesForMessage:(NSString *)text {    return (text.length / [LAXTextView maxCharactersPerLine]) + 1;}#pragma mark - Text view overrides- (void)setText:(NSString *)text {    self.hasText2 = NO;    if (text.length > 0) {        self.hasText2 = YES;        [self notificationAction];    }    [super setText:text];    [self setNeedsDisplay];}- (void)setAttributedText:(NSAttributedString *)attributedText {    [super setAttributedText:attributedText];    [self setNeedsDisplay];}- (void)setFont:(UIFont *)font {    [self setPlaceholderFrame];    self.placeholderFont = font;    self.placeholderLabel.font = font;    [super setFont:font];    [self setNeedsDisplay];}- (void)setTextAlignment:(NSTextAlignment)textAlignment {    [super setTextAlignment:textAlignment];    [self setNeedsDisplay];}- (id)initWithFrame:(CGRect)frame {    if (self = [super initWithFrame:frame]) {        [self setup];    }    return self;}- (void)dealloc {    _placeholder = nil;    _placeholderColor = nil;    [[NSNotificationCenter defaultCenter]removeObserver:UITextViewTextDidChangeNotification];//    [self.KVOController unobserveAll];    //end_code}#pragma mark - custom func- (CGRect)getRectFromString:(NSString *)string fontSize:(UIFont *)font {    NSDictionary *attribute = @{NSFontAttributeName: [UIFont systemFontOfSize:17]};    CGRect rect = [string boundingRectWithSize:CGSizeMake(100, 1000) options: NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading attributes:attribute context:nil];    return rect;}- (void)setPlaceholderFrame {//    self.backgroundColor = [UIColor blueColor];    if (self.placeholderLabel != nil) {//        CGFloat h = [self getRectFromString:_placeholder fontSize:_placeholderFont].size.height;//        NSLog(@"%f", h);        self.placeholderLabel.frame = CGRectMake(3, 7, self.bounds.size.width, 20);//        self.placeholderLabel.backgroundColor = [UIColor redColor];        //self.placeholderLabel.frame = CGRectMake(5, 7, self.bounds.size.width - 20, 20);    }}- (void)setup {    //添加一个通知，监听textview的内容是否改变    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(notificationAction) name:UITextViewTextDidChangeNotification object:self];    self.placeholderLabel = [[UILabel alloc]init];//    self.placeholderLabel.textAlignment = NSTextAlignmentCenter;//    __weak LAXTextView *ws = self;//    self.KVOController = [FBKVOController controllerWithObserver:self];//    [self.KVOController observe:self keyPath:@"frame" options:NSKeyValueObservingOptionNew |NSKeyValueObservingOptionOld block:^(id observer, id object, NSDictionary *change)//     {//         [ws setPlaceholderFrame];//    }];    self.placeholder = @"";    self.placeholderFont = self.font;    self.placeholderColor= [UIColor grayColor];    self.placeholderLabel.backgroundColor = [UIColor clearColor];    self.placeholderLabel.text = _placeholder;    self.placeholderLabel.numberOfLines = 0;    [self addSubview:self.placeholderLabel];    self.font= [UIFont systemFontOfSize:14];}#pragma mark - Notifications- (void)didReceiveTextDidChangeNotification:(NSNotification *)notification {    [self setNeedsDisplay];}- (void)notificationAction{    self.placeholderLabel.hidden = (self.hasText || self.hasText2);    self.placeholderLabel.text = _placeholder;}@end