Textbox value is empty C#

I am new to C# and I am trying to do something very simple. I want to get the value from a textbox, when I press a button, here is my textboxes and C# code. The strange thing is that the values are empty, I saw that when I tried to debug.

This is my client side code -

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
<asp:Button ID="Button1" runat="server" Text="Cauta" OnClick="Button1_Click"/>

This is my server side code -

protected void Button1_Click(object sender, EventArgs e)

        Label1.Text = "test";
        string var;
        var = TextBox1.Text;

        str = "SELECT * FROM test where id="+TextBox1.Text+" and nume="+"'"+TextBox2.Text+"'";
        da = new OracleDataAdapter(str, conn);

Any help will be appreciated. Thanks!