UITextView设置占位文字

这里只介绍一种，这种方便扩展，可以占位文字颜色.

我们继承一个UITextView:

#import <UIKit/UIKit.h>

@interface MyTextView : UITextView

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

@end

#import "MyTextView.h"

@implementation MyTextView


- (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];
}

#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];
}

调用:

    MyTextView *my = [[MyTextView alloc] initWithFrame:CGRectMake(10, 44, [UIScreen mainScreen].bounds.size.width-20, 200)];
    my.placeholder = @"请输入文字";
    //不设置颜色，默认是灰色.
    my.placeholderColor = [UIColor orangeColor];
    //添加边框
    my.layer.borderColor = [UIColor grayColor].CGColor;
    
    my.layer.borderWidth =1.0;
    
    my.layer.cornerRadius =5.0;
    
    [self.view addSubview:my];