Button event trigger twice when all methods fail

i remove onclick below and it will not run, when i add back in Oninit it run twice again. Then i try to use viewstate, it also run twice. Then i try to use if!page.ispostback), it do not run code. What can i do?
 
<asp:Button ID="Save_Button" runat="server" Text="Save" onclick="Save_Button_Click" />  
protected void Save_Button_Click(object sender, EventArgs e) { //if (ViewState["save_min"].ToString() == "allow") if (ViewState["save_min"].ToString() == "allow")
        {
            ViewState["save_min"] = "deny"; string _connectionString = ConfigurationManager.ConnectionStrings["ChequeConnectionString"].ConnectionString; bool exist = false; if (RecordNo_TextBox.Text == "????") { ...