iOS中用UILabel實現UITextView的佔位文字

 

@interface BSPublishTextView : UITextView

/** 對外屬性佔位字符 placeholder */

@property (nonatomic, copy) NSString *placeholder;

 

/** 對外屬性佔位符顏色 */

@property (nonatomic, strong) UIColor *placeholderColor;

@end

@interface BSPublishTextView ()

/** 佔位字符 label */

@property (nonatomic, weak) UILabel *placeholderLabel;

@end

 

@implementation BSPublishTextView

- (UILabel *)placeholderLabel{

    if (!_placeholderLabel) {

        UILabel *placeholderLabel = [[UILabel alloc]init];

        placeholderLabel.numberOfLines = 0;

　　　　 CGRect frame = placeholderLabel.frame;

        frame.origin.x = 4;

        frame.origin.y = 7;

        placeholderLabel.frame = frame;

        [self addSubview:placeholderLabel];

        _placeholderLabel = placeholderLabel;

    }

    return _placeholderLabel;

}

 

- (instancetype)initWithFrame:(CGRect)frame

{

    self = [super initWithFrame:frame];

    if (self) {

        // 永久垂直彈簧效果

        self.alwaysBounceVertical = YES;

        self.font = [UIFont systemFontOfSize:15];

        self.placeholderColor = [UIColor grayColor];

     

        // 註冊textView文字發生改變通知  UITextViewTextDidChangeNotification

        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChange) name:UITextViewTextDidChangeNotification object:nil];    

    }

    return self;

}

 

//通知調用方法

- (void)textChange{

    self.placeholderLabel.hidden = self.hasText;

}

 

- (void)dealloc{

    [[NSNotificationCenter defaultCenter]removeObserver:self];

}

 

- (void)layoutSubviews{

    [super layoutSubviews];

    //在 layoutSubviews 拿到 UITextView的寬度必定是正確的 ，這裏若是外界即便更改了UITextView的寬度這裏也是能算正確的

    //先設置placeholderLabel佔位字符的寬度

    CGRect frame = self.placeholderLabel.frame;

    frame.size.width = self.frame.size.width - 2 * self.placeholderLabel.frame.origin.x;

    self.placeholderLabel.frame = frame;

 

    // placeholderLabel佔位字符的大小size隨裏面的內容大小而變化

    [self.placeholderLabel sizeToFit];

}

 

// setNeedsDisplay方法 : 會在恰當的時刻自動調用drawRect:方法

// setNeedsLayout方法 : 會在恰當的時刻調用layoutSubviews方法

 

- (void)setPlaceholderColor:(UIColor *)placeholderColor{

    _placeholderColor = placeholderColor;

    self.placeholderLabel.textColor = placeholderColor;

}

 

- (void)setPlaceholder:(NSString *)placeholder{

    _placeholder = [placeholder copy];

    self.placeholderLabel.text = placeholder;

    [self setNeedsLayout]; //會在恰當的時刻調用layoutSubviews方法 這句代碼可不寫

}

 

- (void)setFont:(UIFont *)font{

    [super setFont:font];

    self.placeholderLabel.font = font;

    [self setNeedsLayout];  //會在恰當的時刻調用layoutSubviews方法 這句代碼可不寫

}

 

- (void)setText:(NSString *)text{

    [super setText:text];

    [self textChange];

}

 

- (void)setAttributedText:(NSAttributedString *)attributedText{

    [super setAttributedText:attributedText];

    [self textChange];

}

@end