YHPlaceholderTextView.m

//
//  YHPlaceholderTextView.m
//  LGIDExchangeMobile
//
//  Created by YRH on 2017/11/11.
//  Copyright © 2017年 YRH. All rights reserved.
//

#import "YHPlaceholderTextView.h"

@implementation YHPlaceholderTextView

- (instancetype)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        // 设置默认字体
        self.font = [UIFont systemFontOfSize:15];
        // 设置默认颜色
        self.placeholderColor = [UIColor grayColor];
        // 使用通知监听文字改变
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange:) name:UITextViewTextDidChangeNotification object:self];
    }
    return self;
}

- (void)textDidChange:(NSNotification *)note {
    // 会重新调用drawRect:方法
    [self setNeedsDisplay];
}

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

/**
 * 每次调用drawRect:方法，都会将以前画的东西清除掉
 */
- (void)drawRect:(CGRect)rect {
    // 如果有文字，就直接返回，不需要画占位文字
    if (self.hasText) return;
    
    // 属性
    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
    attrs[NSFontAttributeName] = self.font;
    attrs[NSForegroundColorAttributeName] = self.placeholderColor;
    
    // 画文字
    rect.origin.x = 5;
    rect.origin.y = 8;
    rect.size.width -= 2 * rect.origin.x;
    [self.placeholder drawInRect:rect withAttributes:attrs];
}

- (void)layoutSubviews {
    [super layoutSubviews];
    [self setNeedsDisplay];
}

// 设置光标高度
- (CGRect)caretRectForPosition:(UITextPosition *)position {
    CGRect originalRect = [super caretRectForPosition:position];
    originalRect.size.height = 20;
    return originalRect;
}

#pragma mark - setter
- (void)setPlaceholder:(NSString *)placeholder {
    _placeholder = [placeholder copy];
    [self setNeedsDisplay];
}

- (void)setPlaceholderColor:(UIColor *)placeholderColor {
    _placeholderColor = placeholderColor;
    [self setNeedsDisplay];
}

- (void)setFont:(UIFont *)font {
    [super setFont:font];
    [self setNeedsDisplay];
}

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

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