iOS UITextView placeholder方法

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#import <UIKit/UIKit.h>

@interface WTextView : UITextView

@property (weak, nonatomic) NSString *placeholder;

@end

#import "WTextView.h"

@implementation WTextView

- (instancetype)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        // 添加监听器，监听自己的文字改变通知
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textDidChange) name:UITextViewTextDidChangeNotification object:nil];
    }
    return self;
}

// 时刻监听文字键盘文字的变化，文字一旦改变便调用setNeedsDisplay方法
- (void)textDidChange {
    // 该方法会调用drawRect:方法，立即重新绘制占位文字
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect {
    
    if (self.hasText) return;
    
    NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
    attrs[NSFontAttributeName] = self.font;
    attrs[NSForegroundColorAttributeName] = [UIColor lightGrayColor];
    // 在textView的矩形框中绘制文字
    [self.placeholder drawInRect:CGRectMake(5, 5, self.frame.size.width, self.frame.size.height) withAttributes:attrs];
    
}

// 占位文字的setter方法
- (void)setPlaceholder:(NSString *)placeholder {
    _placeholder = placeholder;
    // 文字一旦改变，立马重写绘制（内部会调drawRect:方法）
    [self setNeedsDisplay];
    
}
// 字体属性setter方法
- (void)setFont:(UIFont *)font {
    [super setFont:font];
    [self setNeedsDisplay];
}

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

@end

self.noteTextView.editable = YES;   //禁止输入的方法