UITextView+Placeholder.h

//
//  UITextView+Placeholder.h
//  DongXi
//
//  Created by Gong Hao on 3/6/14.
//  Copyright (c) 2014 Douban Inc. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface UITextView (Placeholder) <UITextViewDelegate>

@property (nonatomic, strong) NSString *placeholderText;
@property (nonatomic, strong) UIColor *placeholderColor;

@end

UITextView+Placeholder.m

//
//  UITextView+Placeholder.m
//  DongXi
//
//  Created by Gong Hao on 3/6/14.
//  Copyright (c) 2014 Douban Inc. All rights reserved.
//

#import <objc/runtime.h>

#import "UITextView+Placeholder.h"

static char const * const kKeyPlaceholderText = "Key+placeholderText";
static char const * const kKeyPlaceholderColor = "Key+placeholderColor";
static char const * const kKeyPalceholderView = "Key+placeholderView";

@implementation UITextField (Placeholder)

@dynamic placeholderText;
@dynamic placeholderColor;

- (NSString *)placeholderText
{
  return objc_getAssociatedObject(self, kKeyPlaceholderText);
}

- (void)setPlaceholderText:(NSString *)placeholderText
{
  objc_setAssociatedObject(self, kKeyPlaceholderText, placeholderText, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
  self.delegate = self;
  [self updatePlaceholder];
}

- (UIColor *)placeholderColor
{
  return objc_getAssociatedObject(self, kKeyPlaceholderColor);
}

- (void)setPlaceholderColor:(UIColor *)placeholderColor
{
  objc_setAssociatedObject(self, kKeyPlaceholderColor, placeholderColor, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
  [self updatePlaceholder];
}

- (void)textViewDidBeginEditing:(UITextView *)textView
{
  [self togglePlaceholder:NO];
  [self becomeFirstResponder];
}

- (void)textViewDidEndEditing:(UITextView *)textView
{
  if ([textView.text isEqualToString:@""]) {
    [self togglePlaceholder:YES];
  }
  [self resignFirstResponder];
}

- (void)updatePlaceholder
{
  UILabel *placeholderView = objc_getAssociatedObject(self, kKeyPalceholderView);

  if (!placeholderView) {
    placeholderView = [[UILabel alloc] initWithFrame:CGRectMake(4, 4, self.frame.size.width, self.font.lineHeight)];
    [self addSubview:placeholderView];
    objc_setAssociatedObject(self, kKeyPalceholderView, placeholderView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
  }

  placeholderView.font = self.font;
  placeholderView.textColor = self.placeholderColor ? self.placeholderColor : [UIColor lightGrayColor];
  if (self.placeholderText) {
    placeholderView.text = self.placeholderText;
    placeholderView.hidden = NO;
  } else {
    placeholderView.hidden = YES;
  }
}

- (void)togglePlaceholder:(BOOL)on
{
  UILabel *placeholderView = objc_getAssociatedObject(self, kKeyPalceholderView);
  if (placeholderView) {
    placeholderView.hidden = !on;
  }
}

@end