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

巴特西

iOS开发小技巧--自定义带有占位文字的TextView(两种方式)

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