iOS中用UILabel实现UITextView的占位文字
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@interface BSPublishTextView : UITextView
/** 对外属性占位字符 placeholder */
@property (nonatomic, copy) NSString *placeholder;
/** 对外属性占位符颜色 */
@property (nonatomic, strong) UIColor *placeholderColor;
@end
@interface BSPublishTextView ()
/** 占位字符 label */
@property (nonatomic, weak) UILabel *placeholderLabel;
@end
@implementation BSPublishTextView
- (UILabel *)placeholderLabel{
if (!_placeholderLabel) {
UILabel *placeholderLabel = [[UILabel alloc]init];
placeholderLabel.backgroundColor = [UIColor greenColor];
placeholderLabel.numberOfLines = 0;
placeholderLabel.x = 4;
placeholderLabel.y = 7;
[self addSubview:placeholderLabel];
_placeholderLabel = placeholderLabel;
}
return _placeholderLabel;
}
- (instancetype)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
// 永久垂直有弹簧效果
self.alwaysBounceVertical = YES;
self.font = [UIFont systemFontOfSize:15];
self.placeholderColor = [UIColor grayColor];
// 注册通知 当收到 UITextViewTextDidChangeNotification textView文字改变时
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChange) name:UITextViewTextDidChangeNotification object:nil];
}
return self;
}
//通知调用方法
- (void)textChange{
self.placeholderLabel.hidden = self.hasText;
}
- (void)dealloc{
[[NSNotificationCenter defaultCenter]removeObserver:self];
}
- (void)layoutSubviews{
[super layoutSubviews];
//在 layoutSubviews 拿到 UITextView的宽度一定是正确的 ，这里如果外界即使更改了UITextView的宽度这里也是能算正确的
//先设置placeholderLabel占位字符的宽度
self.placeholderLabel.width = self.width - 2 * self.placeholderLabel.x;
// placeholderLabel占位字符的大小size随里面的内容大小而变化
[self.placeholderLabel sizeToFit];
}
// 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
- (void)setPlaceholderColor:(UIColor *)placeholderColor{
_placeholderColor = placeholderColor;
self.placeholderLabel.textColor = placeholderColor;
}
- (void)setPlaceholder:(NSString *)placeholder{
_placeholder = [placeholder copy];
self.placeholderLabel.text = placeholder;
[self setNeedsLayout]; //会在恰当的时刻调用layoutSubviews方法 这句代码可不写
}
- (void)setFont:(UIFont *)font{
[super setFont:font];
self.placeholderLabel.font = font;
[self setNeedsLayout]; //会在恰当的时刻调用layoutSubviews方法 这句代码可不写
}
- (void)setText:(NSString *)text{
[super setText:text];
[self textChange];
}
- (void)setAttributedText:(NSAttributedString *)attributedText{
[super setAttributedText:attributedText];
[self textChange];
}
@end
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