意见反馈最常用到的字数限制

-(BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text{
    
    NSString *new = [textView.text stringByReplacingCharactersInRange:range withString:text];
    NSInteger res = kLimitNumber-[new length];
    if(res >= 0){
        _limitLabel.text = [NSString stringWithFormat:@"%ld/%d", (unsigned long)new.length, kLimitNumber];
        return YES;
    }
    else{
        NSRange rg = {0,[text length]+res};
        if (rg.length>0) {
            NSString *s = [text substringWithRange:rg];
            [textView setText:[textView.text stringByReplacingCharactersInRange:range withString:s]];
        }
        // 超过500个的时候
        _limitLabel.text = [NSString stringWithFormat:@"%ld/%d", (unsigned long)kLimitNumber, kLimitNumber];
        return NO;
    }
}