字符个数限制

gistfile1.m

// - (void)viewDidAppear
[[NSNotificationCenter defaultCenter] addObserver:self
                                        selector:@selector(textFieldTextDidChangeNotification:)
                                            name:UITextFieldTextDidChangeNotification
                                          object:nil];

// - (void)viewDidDisappear
[[NSNotificationCenter defaultCenter] removeObserver:self
                                                name:UITextFieldTextDidChangeNotification
                                              object:nil];

#pragma mark - UITextViewTextDidChangeNotification

- (void)textViewTextDidChangeNotification:(NSNotification *)notification
{
    UITextView *textView = (UITextView *)notification.object;
    
    NSString *toBeString = textView.text;
    NSString *lang = [[UITextInputMode currentInputMode] primaryLanguage]; // 键盘输入模式
    if ([lang isEqualToString:@"zh-Hans"]) { // 简体中文输入，包括简体拼音，健体五笔，简体手写
        UITextRange *selectedRange = [textView markedTextRange];
        //获取高亮部分
        // UITextPosition *position = [textView positionFromPosition:selectedRange.start offset:0];
        // 没有高亮选择的字，则对已输入的文字进行字数统计和限制
        if (!selectedRange) {
            
            int length = [StringUtility calculateTextNumber:toBeString];
            
            if (length > MAX_CONTENT) {
                textView.text = [toBeString substringToIndex:[StringUtility calculateSubstringIndex:toBeString
                                                                                              count:MAX_CONTENT]];
            }
        }
        // 有高亮选择的字符串，则暂不对文字进行统计和限制
        else{
            
        }
    }
    // 中文输入法以外的直接对其统计限制即可，不考虑其他语种情况
    else {
        int length = [StringUtility calculateTextNumber:toBeString];
        if (length > MAX_CONTENT) {
            textView.text = [toBeString substringToIndex:[StringUtility calculateSubstringIndex:toBeString
                                                                                          count:MAX_CONTENT]];
        }
    }
}

// StringUtility
+ (int)calculateTextNumber:(NSString *)dataString
{
    float sum = 0.0;
    for(int i=0;i<[dataString length];i++)
    {
        NSString *character = [dataString substringWithRange:NSMakeRange(i, 1)];
        if([character lengthOfBytesUsingEncoding:NSUTF8StringEncoding] == 3)
        {
            sum += 2;
        }
        else
            sum += 1;
    }
    return ceil(sum);
}

+ (int)calculateSubstringIndex:(NSString *)text count:(NSUInteger)count
{
    float number = 0.0;
    for (int index = 0; index < [text length]; index++) {
        
        NSString *character = [text substringWithRange:NSMakeRange(index, 1)];
        
        if ([character lengthOfBytesUsingEncoding:NSUTF8StringEncoding] == 3) {
            number += 2;
        } else {
            number += 1;
        }
        if (number > count) {
            return index;
        }
    }
    return 0;
}