给UITextView加上占位字符代码,ObjC代码库,德仔网

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【ObjC】给UITextView加上占位字符

作者:佳航 / 发布于2014/11/15/ 383

这份代码能够给 UITextView 加上类似 UITextField 那样的占位符（placeholder）。


	//
	// SSTextView.h
	// SSToolkit
	//
	// Created by Sam Soffes on 8/18/10.
	// Copyright 2010-2011 Sam Soffes. All rights reserved.
	//
	
	/**
	UITextView subclass that adds placeholder support like UITextField has.
	*/
	@interface SSTextView : UITextView
	
	/**
	The string that is displayed when there is no other text in the text view.
	
	The default value is `nil`.
	*/
	@property (nonatomic, retain) NSString *placeholder;
	
	/**
	The color of the placeholder.
	
	The default is `[UIColor lightGrayColor]`.
	*/
	@property (nonatomic, retain) UIColor *placeholderColor;
	
	@end
	
	
	//
	// SSTextView.m
	// SSToolkit
	//
	// Created by Sam Soffes on 8/18/10.
	// Copyright 2010-2011 Sam Soffes. All rights reserved.
	//
	
	#import "SSTextView.h"
	
	@interface SSTextView ()
	- (void)_initialize;
	- (void)_updateShouldDrawPlaceholder;
	- (void)_textChanged:(NSNotification *)notification;
	@end
	
	
	@implementation SSTextView {
	 BOOL _shouldDrawPlaceholder;
	}
	
	
	#pragma mark - Accessors
	
	@synthesize placeholder = _placeholder;
	@synthesize placeholderColor = _placeholderColor;
	
	- (void)setText:(NSString *)string {
	 [super setText:string];
	 [self _updateShouldDrawPlaceholder];
	}
	
	
	- (void)setPlaceholder:(NSString *)string {
	 if ([string isEqual:_placeholder]) {
	 return;
	 }
	
	 [_placeholder release];
	 _placeholder = [string retain];
	
	 [self _updateShouldDrawPlaceholder];
	}
	
	
	#pragma mark - NSObject
	
	- (void)dealloc {
	 [[NSNotificationCenter defaultCenter] removeObserver:self name:UITextViewTextDidChangeNotification object:self];
	
	 [_placeholder release];
	 [_placeholderColor release];
	 [super dealloc];
	}
	
	
	#pragma mark - UIView
	
	- (id)initWithCoder:(NSCoder *)aDecoder {
	 if ((self = [super initWithCoder:aDecoder])) {
	 [self _initialize];
	 }
	 return self;
	}
	
	
	- (id)initWithFrame:(CGRect)frame {
	 if ((self = [super initWithFrame:frame])) {
	 [self _initialize];
	 }
	 return self;
	}
	
	
	- (void)drawRect:(CGRect)rect {
	 [super drawRect:rect];
	
	 if (_shouldDrawPlaceholder) {
	 [_placeholderColor set];
	 [_placeholder drawInRect:CGRectMake(8.0f, 8.0f, self.frame.size.width - 16.0f, self.frame.size.height - 16.0f) withFont:self.font];
	 }
	}
	
	
	#pragma mark - Private
	
	- (void)_initialize {
	 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(_textChanged:) name:UITextViewTextDidChangeNotification object:self];
	
	 self.placeholderColor = [UIColor colorWithWhite:0.702f alpha:1.0f];
	 _shouldDrawPlaceholder = NO;
	}
	
	
	- (void)_updateShouldDrawPlaceholder {
	 BOOL prev = _shouldDrawPlaceholder;
	 _shouldDrawPlaceholder = self.placeholder && self.placeholderColor && self.text.length == 0;
	
	 if (prev != _shouldDrawPlaceholder) {
	 [self setNeedsDisplay];
	 }
	}
	
	
	- (void)_textChanged:(NSNotification *)notificaiton {
	 [self _updateShouldDrawPlaceholder];
	}
	
	@end

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　UITextView　　占位字符　

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