本文主要是介绍[iOS]UITextView+Placeholder，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
以前为UITextView的占位符纠结过很多次,使用过多种方式处理过,最近找到了一种别人处理的方式,比较完美.
资源下载,自己下载使用的,会control+c的同学没必要下载,哈哈
// The MIT License (MIT)
//
// Copyright (c) 2014 Suyeol Jeon (http:xoul.kr)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.@import UIKit;FOUNDATION_EXPORT double UITextView_PlaceholderVersionNumber;
FOUNDATION_EXPORT const unsigned char UITextView_PlaceholderVersionString[];@interface UITextView (Placeholder)/* 占位文字 */
@property (nonatomic, copy) NSString *placeholder;
/* 占位文字颜色 */
@property (nonatomic, strong) UIColor *placeholderColor;@end// The MIT License (MIT)
//
// Copyright (c) 2014 Suyeol Jeon (http:xoul.kr)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.#import <objc/runtime.h>
#import "UITextView+Placeholder.h"// 占位文字
static const void *PlaceholderViewKey = &PlaceholderViewKey;
// 占位文字颜色
static const void *PlaceholderColorKey = &PlaceholderColorKey;@implementation UITextView (Placeholder)#pragma mark - Swizzle Dealloc#pragma mark - Swizzle Dealloc
+ (void)load {// 交换dealocMethod dealoc = class_getInstanceMethod(self.class, NSSelectorFromString(@"dealloc"));Method myDealoc = class_getInstanceMethod(self.class, @selector(myDealoc));method_exchangeImplementations(dealoc, myDealoc);
}- (void)myDealoc {// 移除监听[[NSNotificationCenter defaultCenter] removeObserver:self];UITextView *placeholderView = objc_getAssociatedObject(self, PlaceholderViewKey);// 如果有值才去调用，这步很重要if (placeholderView) {NSArray *propertys = @[@"frame", @"bounds", @"font", @"text", @"textAlignment", @"textContainerInset"];for (NSString *property in propertys) {@try {[self removeObserver:self forKeyPath:property];} @catch (NSException *exception) {}}}[self myDealoc];
}#pragma mark - set && get
- (UITextView *)placeholderView {// 为了让占位文字和textView的实际文字位置能够完全一致，这里用UITextViewUITextView *placeholderView = objc_getAssociatedObject(self, PlaceholderViewKey);if (!placeholderView) {placeholderView = [[UITextView alloc] init];placeholderView.hidden = (self.text.length > 0 && self.text);// 动态添加属性的本质是: 让对象的某个属性与值产生关联objc_setAssociatedObject(self, PlaceholderViewKey, placeholderView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);placeholderView = placeholderView;// 设置基本属性self.scrollEnabled = placeholderView.scrollEnabled = placeholderView.showsHorizontalScrollIndicator = placeholderView.showsVerticalScrollIndicator = placeholderView.userInteractionEnabled = NO;placeholderView.textColor = [UIColor lightGrayColor];placeholderView.backgroundColor = [UIColor clearColor];[self refreshPlaceholderView];[self addSubview:placeholderView];// 监听文字改变[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textViewTextChange) name:UITextViewTextDidChangeNotification object:self];// 这些属性改变时，都要作出一定的改变，尽管已经监听了TextDidChange的通知，也要监听text属性，因为通知监听不到setText：NSArray *propertys = @[@"frame", @"bounds", @"font", @"text", @"textAlignment", @"textContainerInset"];// 监听属性for (NSString *property in propertys) {[self addObserver:self forKeyPath:property options:NSKeyValueObservingOptionNew context:nil];}}return placeholderView;
}
- (void)setPlaceholder:(NSString *)placeholder
{// 为placeholder赋值[self placeholderView].text = placeholder;
}- (NSString *)placeholder
{// 如果有placeholder值才去调用，这步很重要if (self.placeholderExist) {return [self placeholderView].text;}return nil;
}- (void)setPlaceholderColor:(UIColor *)placeholderColor
{self.placeholderView.textColor = placeholderColor;}- (UIColor *)placeholderColor {return self.placeholderView.textColor;
}
#pragma mark - KVO监听属性改变
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {[self refreshPlaceholderView];if ([keyPath isEqualToString:@"text"]) [self textViewTextChange];
}- (void)refreshPlaceholderView {UITextView *placeholderView = objc_getAssociatedObject(self, PlaceholderViewKey);// 如果有值才去调用，这步很重要if (placeholderView) {self.placeholderView.frame = self.bounds;self.placeholderView.font = self.font;self.placeholderView.textAlignment = self.textAlignment;self.placeholderView.textContainerInset = self.textContainerInset;}
}- (void)textViewTextChange {UITextView *placeholderView = objc_getAssociatedObject(self, PlaceholderViewKey);// 如果有值才去调用，这步很重要if (placeholderView) {self.placeholderView.hidden = (self.text.length > 0 && self.text);}if (!self.isFirstResponder) [self becomeFirstResponder];
}// 判断是否有placeholder值，这步很重要
- (BOOL)placeholderExist {// 获取对应属性的值UITextView *placeholderView = objc_getAssociatedObject(self, PlaceholderViewKey);// 如果有placeholder值if (placeholderView) return YES;return NO;
}@end
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