自定義UITextView豪诲，在.h中
@interface JJPlaceHTextView : UITextView

/** 占位文字 */
@property (nonatomic, copy) NSString *placeholder;
/** 占位文字顏色 */
@property (nonatomic, strong) UIColor *placeholderColor;

@end
在.m中

- (instancetype)init
{
    if (self = [super init]) {
        // 設置默認字體
        self.font = [UIFont systemFontOfSize:15];
        
        // 設置默認顏色
        self.placeholderColor = ColorA9;
        
        // 使用通知監(jiān)聽文字改變
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange:) name:UITextViewTextDidChangeNotification object:self];
    }
    return self;
}

- (void)textDidChange:(NSNotification *)note
{
    // 會重新調用drawRect:方法
    [self setNeedsDisplay];
}

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

/**
 * 每次調用drawRect:方法劳翰，都會將以前畫的東西清除掉
 */
- (void)drawRect:(CGRect)rect
{
    // 如果有文字绘闷，就直接返回巢价，不需要畫占位文字
    if (self.hasText) return;
    
    // 屬性
    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
    attrs[NSFontAttributeName] = self.font;
    attrs[NSForegroundColorAttributeName] = self.placeholderColor;
    
    // 畫文字
    rect.origin.x = 0;
    rect.origin.y = 8;
    rect.size.width -= 2 * rect.origin.x;
    [self.placeholder drawInRect:rect withAttributes:attrs];
}

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

#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];
}