为UITextView增加占位文字的封装

1.新建继承UITextView的类

定义可以对外访问用于修改的属性

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

在.m文件定义一个label

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

懒加载把label添加到textView中

 
 
 
  
(UILabel *)placeholderLabel
 {
 if (!_placeholderLabel) {
 // 添加一个用来显示占位文字的label
 UILabel *placeholderLabel = [[UILabel alloc] init];
 placeholderLabel.numberOfLines = 0;
 placeholderLabel.x = 4;
 placeholderLabel.y = 7;
 [self addSubview:placeholderLabel];
 _placeholderLabel = placeholderLabel;
 }
 return _placeholderLabel;
 }
 参考文章：UIView扩展-直接用点语法改变UIView的尺寸http://www.jianshu.com/p/4e00189dea2b
 

初始化一些设置

 
 
 
  
 
(instancetype)initWithFrame:(CGRect)frame
 {
 if (self = [super initWithFrame:frame]) {
 // 垂直方向上永远有弹簧效果
 self.alwaysBounceVertical = YES;
 
  // 默认字体
  self.font = [UIFont systemFontOfSize:15];
  
  // 默认的占位文字颜色
  self.placeholderColor = [UIColor grayColor];
  
  // 监听文字改变
  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:nil];
 
}
 return self;
 }
 
 
  
(void)textDidChange
 {
 // 只要有文字, 就隐藏占位文字label
 self.placeholderLabel.hidden = self.hasText;
 }
 
 
 
 

移除通知

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

更新占位文字的尺寸

 
 
 
  
 
(void)layoutSubviews
 {
 [super layoutSubviews];
 
self.placeholderLabel.width = self.width - 2 * self.placeholderLabel.x;
 [self.placeholderLabel sizeToFit];
 }
 参考文章：UIView扩展-直接用点语法改变UIView的尺寸http://www.jianshu.com/p/4e00189dea2b
 

重写相关的setting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];
 }
 
 
  
 
(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];
 }
 

封装的类的下载地址https://git.oschina.net/qjz.com/TextView_placeholderLabel/tree/master