iOS:键盘中文限制

 [textField addTarget:self action:@selector(textFieldDidChange:) forControlEvents:(UIControlEventEditingChanged)];

- (void)textFieldDidChange:(UITextField *)textField
{
    if(_maxLength <= 0){
        return;
    }
    
    NSString *text = textField.text;
    UITextRange *selectedRange = [textField markedTextRange];
    UITextPosition *position = [textField 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,防止中文/emoj被截断
    if (!position){
        if (text.length > _maxLength){
            NSRange rangeIndex = [text rangeOfComposedCharacterSequenceAtIndex:_maxLength];
            if (rangeIndex.length == 1){
                textField.text = [text substringToIndex:_maxLength];
            }else{
                if(_maxLength == 1){
                    textField.text = @"";
                }else{
                    NSRange rangeRange = [text rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, _maxLength - 1 )];
                    textField.text = [text substringWithRange:rangeRange];
                }
            }
            
        }
    }
}