warmlight/LimitTextView · GitHub

 //限制输入的字数（以中文为单位），不赋值就是不限制字数
@property (assign, nonatomic) NSInteger limteNum; 
	
　 　//根据输入文本自适应行高，默认不自适应    
@property (assign, nonatomic) BOOL autoHeight; 
	
//placehold的文字，不设置就不显示       
@property (strong, nonatomic) NSString *placeHold;
	
//placehold的font，如果用到placehold才设置
//因为placehold自适应行高需要知道字号 
@property (strong, nonatomic) UIFont *placeHoldFont;
    }];

	- (void)textViewDidChange:(UITextView *)textView
	{
    if (self.placeHold.length > 0) {
        //textview没有placeholder，模仿placeholder的状态来控制placeholderLabel的显示和消失
        //textview长度为0
        if (self.text.length==0){
           	 self.placeHoldLabel.hidden = NO;
        }
        else{
            self.placeHoldLabel.hidden=YES;
        }
    }
    
    UITextRange *selectedRange = [textView markedTextRange];
    //获取高亮部分
    UITextPosition *pos = [textView positionFromPosition:selectedRange.start offset:0];
    
    //如果在变化中是高亮部分在变，就不计算字符
    if (selectedRange && pos) {
        return;
    }
    
    //超过规定的字数时
    //charNumber这个方法是NSString的一个catetory
    //因为是以中文两个字节，英文一个字节处理，所以把字数×２
    if ([textView.text charNumber] > self.limteNum * 2) {
        //判断是否是普通的字符或asc码，我就是拿来判断是不是纯英文
        BOOL asc = [textView.text canBeConvertedToEncoding:NSASCIIStringEncoding];
        if (asc){
            //是纯英文就好办，可以直接截取相应的字符数用来显示
            NSString *str = [textView.text substringToIndex:self.limteNum * 2];
            if ([self.limitdelegate respondsToSelector:@selector(beyondLimitNum)]) {
                [self.limitdelegate beyondLimitNum];
            }
            [textView setText:str];
        }else{
            //如果是中英文混合输入，那么就不能单纯用substringToIndex截取，因为它一视同仁
            //不管中英文都当做一个单位来截断
            __block NSString *str = [[NSString alloc] init];
            __block NSInteger num = 0;
            __weak LimitTextView * bSelf = self;
            //逐字遍历，不管是中文英文，中文就按照字，英文就是按字母
            [textView.text enumerateSubstringsInRange:NSMakeRange(0, [textView.text length])
                                              options:NSStringEnumerationByComposedCharacterSequences
                                           usingBlock: ^(NSString* substring, NSRange substringRange, NSRange enclosingRange, BOOL* stop) {
                                               NSInteger subLen = [substring charNumber];
                                               num += subLen;
                                               NSLog(@"%d", num);
                                               if (num <= self.limteNum * 2) {
                                                   str  = [str stringByAppendingString:substring];
                                               }else{
                                                   if ([bSelf.limitdelegate respondsToSelector:@selector(beyondLimitNum)]) {
                                                       [bSelf.limitdelegate beyondLimitNum];
                                                   }
                                                   return;
                                               }
                                           }];
            [textView setText:str];
        }
    }
    
    //滚动到一个特定区域
    [self textViewIndicateMoveToCurrentPosition];
    //随着输入越多字数，textview不断变高
    if (self.autoHeight) {
        if (self.contentSize.height > self.frame.size.height){
            CGRect frame = self.frame;
            frame.size.height = self.contentSize.height;
            self.frame = frame;
        }
    }
	}

	#import "ViewController.h"
	#import "LimitTextView.h"
	@interface ViewController ()<LimitTextViewDelegate>

	@end

	@implementation ViewController

	- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    
    LimitTextView *tx = [[LimitTextView alloc]initWithFrame:CGRectMake(0, 60, self.view.frame.size.width, 80)];
    tx.backgroundColor = [UIColor lightGrayColor];
    tx.limteNum = 5;
    tx.autoHeight = YES;
    tx.placeHoldFont = [UIFont systemFontOfSize:13];
    tx.placeHold = @"我是placeholder,我的行高可以改变！！！！";
    tx.limitdelegate = self;
    [self.view addSubview:tx];
	}

	//如果超出了限制字数会走这个delegate，可以把提示的逻辑写到这个里面
	- (void)beyondLimitNum {
	    NSLog(@"超过了限制字数( ⊙ o ⊙ )啊！");
	}