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