給TextView添加占位符

//
//  HYBTextView.h
//
//  Created by huangyibiao on 14-6-3.
//  Copyright (c) 2014年 huangyibiao. All rights reserved.
//

#import <UIKit/UIKit.h>

/*!
 * @brief 繼承于UITextView，添加了placeholder支援，就像UITextField一樣的擁有placeholder功能
 * @author huangyibiao
 */
@interface HYBTextView : UITextView

/*!
 * @brief 占位符文本,與UITextField的placeholder功能一緻
 */
@property (nonatomic, strong) NSString *placeholder;

/*!
 * @brief 占位符文本顔色
 */
@property (nonatomic, strong) UIColor *placeholderTextColor;

@end
           

//
//  HYBTextView.m
//  HomeLinkProject
//
//  Created by huangyibiao on 14-6-3.
//  Copyright (c) 2014年 huangyibiao. All rights reserved.
//

#import "HYBTextView.h"

@interface HYBTextView () {
    BOOL _shouldDrawPlaceholder;
}

@end

@implementation HYBTextView

#pragma mark - 重寫父類方法
- (void)setText:(NSString *)text {
    [super setText:text];
    [self drawPlaceholder];
    return;
}

- (void)setPlaceholder:(NSString *)placeholder {
    if (![placeholder isEqual:_placeholder]) {
        _placeholder = placeholder;
        [self drawPlaceholder];
    }
    return;
}

#pragma mark - 父類方法
- (id)initWithCoder:(NSCoder *)aDecoder {
    if (self = [super initWithCoder:aDecoder]) {
        [self configureBase];
    }
    return self;
}

- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        [self configureBase];
    }
    return self;
}

- (void)drawRect:(CGRect)rect {
    [super drawRect:rect];
    if (_shouldDrawPlaceholder) {
        [_placeholderTextColor set];
        [_placeholder drawInRect:CGRectMake(8.0f, 8.0f, self.frame.size.width - 16.0f,
                                            self.frame.size.height - 16.0f) withFont:self.font];
    }
    return;
}

- (void)configureBase {
    [kNotificationCenter addObserver:self
                            selector:@selector(textChanged:)
                                name:UITextViewTextDidChangeNotification
                              object:self];
	
	self.placeholderTextColor = [UIColor colorWithWhite:0.702f alpha:1.0f];
	_shouldDrawPlaceholder = NO;
    return;
}

- (void)drawPlaceholder {
    BOOL prev = _shouldDrawPlaceholder;
	_shouldDrawPlaceholder = self.placeholder && self.placeholderTextColor && self.text.length == 0;
	
	if (prev != _shouldDrawPlaceholder) {
		[self setNeedsDisplay];
	}
    return;
}

- (void)textChanged:(NSNotification *)notification {
    [self drawPlaceholder];
    return;
}

- (void)dealloc {
    [kNotificationCenter removeObserver:self name:UITextViewTextDidChangeNotification object:nil];
    return;
}

@end