思路：
1、通过runtime添加两个字符串属性，供外接访问。一个为设置占位字符串（placeholder）使用，一个为设置最大文字个数（limitLength）使用。
2、通过runtime将UITextView和两个UILabel关联起来，一个用做显示占位字符串（placeholderLabel）使用，一个用做显示最大文字个数（wordCountLabel）使用。
3、在占位字符串（placeholder）和最大文字个数（limitLength）的set方法中分别调用第二步中两个UILabel的初始化方法。
4、注册两个通知（通知的名字都叫：UITextViewTextDidChangeNotification，但监听方法不一样）：一个用作监听UITextView输入字数，有则不显示占位文字，没有就显示占位文字。另一个用作监听是否超过最大输入字数使用，没有超过可继续使用，超过则截取到最大字数，后面的不显示，也无法输入。（倘若提示用户超出最大字数，可以在通知的监听方法中判断提示）
效果图如下：
效果图
此分类使用的时候，只是在正常创建UITextView时多了两个属性设置：
self.addessalDetailTextView.placeholder = @"请填写详细地址，不少于120个字";
self.addessalDetailTextView.limitLength = @120;
具体使用代码如下（是不是代码很少）：
UITextView *textView = [[UITextView alloc] init];
textView.frame = CGRectMake(10, 10, 300, 150);
textView.center = self.view.center;
textView.placeholder = @"请填写详细地址，不多于120个字";
textView.limitLength = @120;
[self.view addSubview:textView];
也可以使用xib关联，简单方便。
下面就看分类（UITextView+CLTextView）的具体实现：
1、UITextView+CLTextView.h的实现，这也就是思路中的第一步
@property (nonatomic,strong) NSString *placeholder;//占位符
@property (copy, nonatomic) NSNumber *limitLength;//字数限制
2、UITextView+CLTextView.m的实现
引入#import <objc/runtime.h>头文件
@interface UITextView ()
@property (nonatomic,strong) UILabel *placeholderLabel;//占位符
@property (nonatomic,strong) UILabel *wordCountLabel;//计算字数
@end
@implementation UITextView (YLTextView)
static NSString *PLACEHOLDLABEL = @"placelabel";
static NSString *PLACEHOLD = @"placehold";
static NSString *WORDCOUNTLABEL = @"wordcount";
static const void *limitLengthKey = &limitLengthKey;
#pragma mark -- setter/getter方法
//显示占位符label的setter/getter方法
-(void)setPlaceholderLabel:(UILabel *)placeholderLabel {
objc_setAssociatedObject(self, &PLACEHOLDLABEL, placeholderLabel, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (UILabel *)placeholderLabel {
return objc_getAssociatedObject(self, &PLACEHOLDLABEL);
}
//显示字数label的setter/getter方法
- (void)setWordCountLabel:(UILabel *)wordCountLabel {
objc_setAssociatedObject(self, &WORDCOUNTLABEL, wordCountLabel, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (UILabel *)wordCountLabel {
return objc_getAssociatedObject(self, &WORDCOUNTLABEL);
}
//供外接访问的占位字符串，以便设置占位文字的setter/getter方法
- (void)setPlaceholder:(NSString *)placeholder {
objc_setAssociatedObject(self, &PLACEHOLD, placeholder, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
[self setPlaceHolderLabel:placeholder];
}
- (NSString *)placeholder {
return objc_getAssociatedObject(self, &PLACEHOLD);
}
//供外接访问的最大输入字数，设置最大文字个数的setter/getter方法
- (NSNumber *)limitLength {
return objc_getAssociatedObject(self, limitLengthKey);
}
- (void)setLimitLength:(NSNumber *)limitLength {
objc_setAssociatedObject(self, limitLengthKey, limitLength, OBJC_ASSOCIATION_COPY_NONATOMIC);
[self addLimitLengthObserver:[limitLength intValue]];
[self setWordcountLable:limitLength];
}
#pragma mark -- 配置占位符标签
- (void)setPlaceHolderLabel:(NSString *)placeholder {
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textFieldChanged:) name:UITextViewTextDidChangeNotification object:self];
// 占位字符
self.placeholderLabel = [[UILabel alloc] init];
self.placeholderLabel.font = [UIFont systemFontOfSize:13.];
self.placeholderLabel.text = placeholder;
self.placeholderLabel.numberOfLines = 0;
self.placeholderLabel.lineBreakMode = NSLineBreakByWordWrapping;
self.placeholderLabel.textColor = [UIColor lightGrayColor];
CGRect rect = [placeholder boundingRectWithSize:CGSizeMake(CGRectGetWidth(self.frame)-7, CGFLOAT_MAX) options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName: [UIFont systemFontOfSize:13.]} context:nil];
self.placeholderLabel.frame = CGRectMake(7, 7, rect.size.width, rect.size.height);
[self addSubview:self.placeholderLabel];
self.placeholderLabel.hidden = self.text.length > 0 ? YES : NO;
}
#pragma mark -- 设置字数限制标签
- (void)setWordcountLable:(NSNumber *)limitLength {
//字数限制
self.wordCountLabel = [[UILabel alloc] initWithFrame:CGRectMake(CGRectGetWidth(self.frame) - 65, CGRectGetHeight(self.frame) - 20, 60, 20)];
self.wordCountLabel.textAlignment = NSTextAlignmentRight;
self.wordCountLabel.textColor = [UIColor lightGrayColor];
self.wordCountLabel.font = [UIFont systemFontOfSize:13.];
if (self.text.length > [limitLength integerValue]) {
self.text = [self.text substringToIndex:[self.limitLength intValue]];
}
self.wordCountLabel.text = [NSString stringWithFormat:@"%lu/%@",(unsigned long)self.text.length,limitLength];
[self addSubview:self.wordCountLabel];
}
#pragma mark -- 注册限制位数的通知
- (void)addLimitLengthObserver:(int)length {
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(limitLengthEvent) name:UITextViewTextDidChangeNotification object:self];
}
#pragma mark -- 限制输入的位数
- (void)limitLengthEvent {
if ([self.text length] > [self.limitLength intValue]) {
self.text = [self.text substringToIndex:[self.limitLength intValue]];
}
}
#pragma mark -- NSNotification
- (void)textFieldChanged:(NSNotification *)notification {
if (self.placeholder) {
self.placeholderLabel.hidden = YES;
if (self.text.length == 0) {
self.placeholderLabel.hidden = NO;
}
}
if (self.limitLength) {
NSInteger wordCount = self.text.length;
if (wordCount > [self.limitLength integerValue]) {
wordCount = [self.limitLength integerValue];
#pragma mark -- 想提示用户输入已经超出最大字数可以打开此行代码
// UIAlertView *view = [[UIAlertView alloc] initWithTitle:@"超过最大字数" message:@"您已经超出了最大字数,超出部分将无法显示" delegate:self cancelButtonTitle:@"取消" otherButtonTitles:@"确定", nil];
// [view show];
}
self.wordCountLabel.text = [NSString stringWithFormat:@"%ld/%@",wordCount,self.limitLength];
}
}
