一、限制字数输入的方法

1.在UITextFieldDelegate的代理方法中可以限制输入

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if (textField == self.TextField) {
        if (string.length == 0) return YES;
        
        NSInteger existedLength = textField.text.length;
        NSInteger selectedLength = range.length;
        NSInteger replaceLength = string.length;
        if (existedLength - selectedLength + replaceLength > 11) {
            return NO;
        }
    }
    }
    return YES;
}

还可以在其中截取请11个字

if (textField == TextFeild) {
        NSInteger existedLength = textField.text.length;
        NSInteger selectedLength = range.length;
        NSInteger replaceLength = string.length;
        NSString *nameString = [NSString stringWithFormat:@"%@%@",textField.text,string];
        
        if (existedLength - selectedLength + replaceLength > 11) {
            textField.text = [nameString substringToIndex:11];            
            return NO;
        }
    }

2.同样的方法，在textview的- (void)textViewDidChange:(UITextView *)textView；中也可以限制字数输入

- (void)textViewDidChange:(UITextView *)textView{    
    if (textField == _phoneNumberTextFeild) {
        CGFloat maxLength = 11;        
        NSString *toBeString = textField.text;        
        //获取高亮部分
        UITextRange *selectedRange = [textField markedTextRange];
        UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];
        if (!position || !selectedRange)
        {
            if (toBeString.length > maxLength)
            {
                NSRange rangeIndex = [toBeString rangeOfComposedCharacterSequenceAtIndex:maxLength];
                 textField.text = [toBeString substringToIndex:11];                
            }
        }
    }
}

这是两种比较简单的方法，大家可以使用

二、对输入框高亮部分的处理

1.避免高亮状态触发限制字数

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text {

    UITextRange *selectedRange = [textView markedTextRange];
    NSString *newText = [textView textInRange:selectedRange]; //获取高亮部分
    if (newText.length>0 && textView == _leaveTextView) {
        return YES;
    }
   
    return YES;
}

2.输入结束后对输入框处理

- (void)textViewDidChange:(UITextView *)textView {
    UITextRange *selectedRange = [textView markedTextRange];
    NSString *newText = [textView textInRange:selectedRange]; //获取高亮部分
    if (newText.length>0 && textView == _TextView) {
        _leavePlaceLabel.hidden = YES;
    } else {
        // 限制最大字数
        if (textView.text.length > 120) {
            textView.text = [string substringToIndex:120];
            [WDAlert showAlertWithMessage:@"最多输入120字" time:1.0];
        }
    }
    if (textView == _leaveTextView) {
        if ([textView.text isEqualToString:@""]) {
            _placeLabel.hidden = NO;
           
        } else {
            _placeLabel.hidden = YES;
           
        }
}

三、截取字符串时，对表情符号截取的处理

  使用substringToIndex进行字符串截取，这样做有一个潜在的问题，那就是当截取的index恰好是一个表情符号的时候，因为一个emoij在字符串的length并不等于1，这样就会把表情符号分割开来，从而造成整个字符串不显示或者最后一个字符是乱码。一半的emoji的时候，把字符串进行UTF8String转码后为NULL。
  所以截取时需要判断表情符号的位置

-(NSString *)subStringWith:(NSString *)string ToIndex:(NSInteger)index{
    NSString *result = string;
    if (result.length > index) {
        NSRange rangeIndex = [result rangeOfComposedCharacterSequenceAtIndex:index];
        result = [result substringToIndex:(rangeIndex.location)];
    }
    return result;
}

此时就可以截取到正确的字符串了。