ios UITextView设置站位文字

1、很多需求中有需要多行输入，需要站位文字的输入框，这时候最好使用UITextView，下面就新建一个类，继承自UITextView

#import 

@interface PlaceholderTextView : UITextView

/** 占位符*/
@property (copy ,nonatomic) NSString *placeholder;
/** 占位符颜色*/
@property (strong ,nonatomic) UIColor *placeholderColor;
/** 占位符字号*/
@property (strong ,nonatomic) UIFont *placeholderFont;
/** 占位符尺寸*/
@property (assign ,nonatomic) CGRect placeholderRect;


@end

#import "PlaceholderTextView.h"

@interface PlaceholderTextView()

@end

@implementation PlaceholderTextView

- (instancetype)initWithFrame:(CGRect)frame{
    if (self = [super initWithFrame:frame]) {
//        self.font = [UIFont systemFontOfSize:15];
        self.placeholderColor = [UIColor grayColor];
        // 监听文字改变
        [QFMNotiCenter addObserver:self selector:@selector(textDidChange:) name:UITextViewTextDidChangeNotification object:nil];
    }
    return self;
}


/**
 *绘制站位文字 (每次调用此方法之前，会自动清除掉之前的内容)
 */
- (void)drawRect:(CGRect)rect {
    
    // 如果有文字，直接返回，不绘制站位文字
//    if (self.text.length || self.attributedText.length) return;
    if (self.hasText) return;

    // 处理rect
    rect.origin.x = 3;
    rect.origin.y = 7;
    rect.size.width -= 2*rect.origin.x;
    
    // 文字属性
    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
    attrs[NSFontAttributeName] = self.placeholderFont;
    attrs[NSForegroundColorAttributeName] = self.placeholderColor;
//    [self.placeholder drawInRect:CGRectMake(3, 7, self.width, self.height) withAttributes:attrs];
    [self.placeholder drawInRect:rect withAttributes:attrs];
    
}

- (void)textDidChange:(UITextView *)textView{
    QFMLOGFUNC;
    [self setNeedsDisplay];
}


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


#pragma mark - **************** 重写setter 防止外部改写属性
- (void)setPlaceholder:(NSString *)placeholder{
    _placeholder = [placeholder copy];
    [self setNeedsDisplay];
}

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

- (void)setPlaceholderFont:(UIFont *)placeholderFont{
    _placeholderFont = placeholderFont;
    [self setNeedsDisplay];
}
- (void)setText:(NSString *)text{
    [super setText:text];
    [self setNeedsDisplay];
}

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

2、第二种方法

.m文件

#import "PlaceholderTextView.h"

@interface PlaceholderTextView()

/** 站位文字label*/
@property(weak ,nonatomic)UILabel *placeholderLabel;

@end

@implementation PlaceholderTextView

#pragma mark - **************** 第二种方法

-(UILabel *)placeholderLabel{
    if (!_placeholderLabel) {
        // 添加一个用来显示站位文字的label
        UILabel *placeholderLabel = [[UILabel alloc] init];
//        placeholderLabel.hidden = YES;
        placeholderLabel.x = 4;
        placeholderLabel.y = 7;
        placeholderLabel.numberOfLines = 0;
        [self addSubview:placeholderLabel];
        self.placeholderLabel = placeholderLabel;
    }
    return _placeholderLabel;
}

-(instancetype)initWithFrame:(CGRect)frame{
    if (self = [super initWithFrame:frame]) {
        // 竖直方向永远可以拖动
        self.alwaysBounceVertical = YES;
        self.font = [UIFont systemFontOfSize:15];
        // 默认的站位文字颜色
        self.placeholderColor = [UIColor grayColor];
        [QFMNotiCenter addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:nil];
    }
    return self;
}

/*
 *更新站位文字尺寸
* */
- (void)updatePlaceholderLabelSize{
    CGSize placeholderSize = CGSizeMake(self.width - 2*self.placeholderLabel.x, MAXFLOAT);
    self.placeholderLabel.size = [self.placeholder boundingRectWithSize:placeholderSize options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:self.font} context:nil].size;

//self.placeholderLabel.width = SCREEN_WIDTH - 2*self.placeholderLabel.x;
  //  [self.placeholderLabel sizeToFit]; 此方法亦可以

}

#pragma mark - **************** 重新setter
-(void)setPlaceholderColor:(UIColor *)placeholderColor{
    _placeholderColor = placeholderColor;
    self.placeholderLabel.textColor = placeholderColor;
}

- (void)setPlaceholder:(NSString *)placeholder{
    _placeholder = [placeholder copy];
    self.placeholderLabel.text = placeholder;
    [self updatePlaceholderLabelSize];
}

- (void)setFont:(UIFont *)font{
    [super setFont:font];
    self.placeholderLabel.font = font;
    [self updatePlaceholderLabelSize];
}

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

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


- (void)textDidChange{

    self.placeholderLabel.hidden = self.hasText;
}
- (void)dealloc{
    [QFMNotiCenter removeObserver:self];
}


@end

3、第三种方法

#pragma mark - **************** 第三种方法

-(UILabel *)placeholderLabel{
    if (!_placeholderLabel) {
        // 添加一个用来显示站位文字的label
        UILabel *placeholderLabel = [[UILabel alloc] init];
        //        placeholderLabel.hidden = YES;
        placeholderLabel.x = 4;
        placeholderLabel.y = 7;
        placeholderLabel.numberOfLines = 0;
        [self addSubview:placeholderLabel];
        self.placeholderLabel = placeholderLabel;
    }
    return _placeholderLabel;
}

-(instancetype)initWithFrame:(CGRect)frame{
    if (self = [super initWithFrame:frame]) {
        // 竖直方向永远可以拖动
        self.alwaysBounceVertical = YES;
        self.font = [UIFont systemFontOfSize:15];
        // 默认的站位文字颜色
        self.placeholderColor = [UIColor grayColor];
        [QFMNotiCenter addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:nil];
    }
    return self;
}


- (void)layoutSubviews{
    [super layoutSubviews];
    // 根据textView的宽度计算placeholder的宽度
    self.placeholderLabel.width = self.width - 2*self.placeholderLabel.x;
    [self.placeholderLabel sizeToFit];
    
}

#pragma mark - **************** 重新setter
-(void)setPlaceholderColor:(UIColor *)placeholderColor{
    _placeholderColor = placeholderColor;
    self.placeholderLabel.textColor = placeholderColor;
}

- (void)setPlaceholder:(NSString *)placeholder{
    _placeholder = [placeholder copy];
    self.placeholderLabel.text = placeholder;
    [self setNeedsLayout];
}

- (void)setFont:(UIFont *)font{
    [super setFont:font];
    self.placeholderLabel.font = font;
    [self setNeedsLayout];
}

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

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


- (void)textDidChange{

    self.placeholderLabel.hidden = self.hasText;
}
- (void)dealloc{
    [QFMNotiCenter removeObserver:self];
}


/**
 * setNeedsDisplay方法：会在恰当的时刻自动调用drawRect方法
 * setNeedsLayout方法：会在恰当的时刻调用layoutSubViews方法
 */
@end

此方法更为严谨

用label设置的一个好处是，站位文字可以拖动