UITextView添加占位文字和占位文字颜色

具体实现

.h文件

#import <UIKit/UIKit.h>

@interface FMTextViewPlaceholder : UITextView

/** 占位文字 */
@property (nonatomic, strong) NSString *placeholderWord;

/** 占位文字颜色 */
@property (nonatomic, weak) UIColor *placeholderColor;

@end

.m文件
#import "FMTextViewPlaceholder.h"

@implementation FMTextViewPlaceholder

- (void)awakeFromNib {
    [super awakeFromNib];
    
    self.font = [UIFont systemFontOfSize:15];
    
    // 监听文字的改变
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange:) name:UITextViewTextDidChangeNotification object:self];
}

- (instancetype)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        
        self.font = [UIFont systemFontOfSize:15];
        
        // 监听文字的改变
        [[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];
}

#pragma mark - setter方法
- (void)setPlaceholderWord:(NSString *)placeholderWord {
    _placeholderWord = placeholderWord;
    
    // 重绘
    [self setNeedsDisplay];
}


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


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

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

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

#pragma mark - 系统方法

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

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

/**
 *  每次调用这个方法就会把上一次绘制清空
 *
 */
- (void)drawRect:(CGRect)rect {
    if (self.hasText) return;
    
    // 属性
    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
    
    attrs[NSFontAttributeName] = self.font;
    
    attrs[NSForegroundColorAttributeName] = self.placeholderColor;
    
    // 绘文字
    rect.origin.x = 5,
    rect.origin.y = 8;
    rect.size.width -= rect.origin.x * 2;
    
    [self.placeholderWord drawInRect:rect withAttributes:attrs];
}

@end