iOS开发小技巧--自定义带有占位文字的TextView(两种方式)

自定义控件注意或框架注意:自己暴露在外面的属性,一定要重写setter,保证外界与内部的交互性

一.方案一:通过drawRect:方法将文字画到textView中,监听文字改变用的是通知中心(代理也可以监听文字改变,但是这种方式就成了自己作为自己的代理了,不推荐这种方法)发出的消息

UITextViewTextDidChangeNotification.自己监听通知.

• 对外界提供两个属性

• 内部实现

 #import "ChaosPlaceholdTextView.h"

 @implementation ChaosPlaceholdTextView

 - (instancetype)initWithFrame:(CGRect)frame
 {
     if (self = [super initWithFrame:frame]) {

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

         // 外界文字颜色不设置,默认为灰色
         self.placeholdColor = [UIColor grayColor];
     }
     return self;
 }

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

 - (void)textChange
 {
     [self setNeedsDisplay];
 }

 // 调用drawRect时,会将之前的图像擦除掉,重新绘制
 - (void)drawRect:(CGRect)rect {

     if ([self hasText]) return;

     rect.origin.y += ( + );
     rect.origin.x += ;
     rect.size.width -=  * rect.origin.x;

     NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
     attrs[NSForegroundColorAttributeName] = self.placeholdColor;
     attrs[NSFontAttributeName] = [UIFont systemFontOfSize:];
     [self.placehold drawInRect:rect withAttributes:attrs];
 }

 // 设计框架需注意,给外界提供了属性后,一定重写出行的setter,这样既可以时时监听使用者对属性的更改,还可以跟好的与外界代码进行交互
 - (void)setPlacehold:(NSString *)placehold
 {
     _placehold = placehold;
     // 设置了站位文字后,需要重绘一遍
     [self setNeedsDisplay];
 }

 - (void)setPlaceholdColor:(UIColor *)placeholdColor
 {
     _placeholdColor = placeholdColor;
     [self setNeedsDisplay];
 }

 // 同时,也要考虑到
 - (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];
 }

 @end

• 缺点:由于是画上去的,当设置了textView的alwaysBounceHorizontal属性后,不能跟随着scrollView的滑动而滑动,如下图

方案二:通过给TextView添加一个Label,也是通过监听文字改变的通知,修改label的hidden属性.

 #import "ChaosPlaceholdTextView.h"

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

 @implementation ChaosPlaceholdTextView

 - (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 = ;
         placeholderLabel.x = ;
         placeholderLabel.y = ;
         [self addSubview:placeholderLabel];
         _placeholderLabel = placeholderLabel;
     }
     return _placeholderLabel;
 }

 - (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:];

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

 /**
  * 监听文字改变
  */
 - (void)textDidChange
 {
     // 只要有文字, 就隐藏占位文字label
     self.placeholderLabel.hidden = self.hasText;
 }

 /**
  * 更新占位文字的尺寸
  */
 - (void)updatePlaceholderLabelSize
 {
     CGSize maxSize = CGSizeMake(ChaosScreenW -  * self.placeholderLabel.x, MAXFLOAT);
     self.placeholderLabel.size = [self.placeholder boundingRectWithSize:maxSize options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName : self.font} context:nil].size;
 }

 #pragma mark - 重写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];
 }

 @end