Prevent an error While adding same key in HashTable

A HashTabe items are key-value pair, so to add the item you should have a unique key and a value. Before adding a pair to hashtable just check if key already exist and if exist do not insert it otherwise it will through a exception.

Suppose you already have a hashtable :-

Hashtable EmpHashTable = new EmpHashTable();
EmpHashTable.Add("Key1", "Akiii");
EmpHashTable.Add("Key2", "Sharad");
EmpHashTable.Add("Key3", "Anirban");

Now in a button click, we will check if that key is already there or not, if it is there then we will increment the value of the key and insert it :-

protected void btnAdd_Click(object sender, EventArgs e)
    {
        if (txtValue.Text.Trim() != "")
        {
            string strKey = "";
            if (txtKey.Text.Trim() == "")
                strKey = "Key" + (EmpHashTable.Keys.Count + 1);
 
            if (!EmpHashTable.ContainsKey(strKey))
            {
                EmpHashTable.Add(strKey, txtValue.Text.Trim());
 
                ListBoxCloths.DataSource = EmpHashTable;
                ListBoxCloths.DataBind();
                lblMessage.Text = "Hashtable Item Added";
            }
            else
            {
                lblMessage.Text = "Key Already Exist, Enter Another Key";
            }
 
        }
        else
        {
            lblMessage.Text = "Please Enter an Item to Add";
        }
 
    }

Thanks and Regards
Akiii