DropDownList's SelectedIndexChanged event calls all events - asp.net

Question

i'm using Asp .Net Web Forms. i have 2 dropDown list and 1 input field. I want when i change the item on the dropDown list or the field value to call some event but it calls all the events.
for example if i change size it calls Size_SelectedIndexChanged, then Color_SelectedIndexChanged, and then txtKolicina_TextChanged
if i change color it calls Color_SelectedIndexChanged, than Size_SelectedIndexChanged and then txtKolicina_TextChanged.
Any help?
<asp:DropDownList ID="Colors" runat="server" AutoPostBack="true" CssClass="form-control detal-page-input" Style="height: 30px;" OnSelectedIndexChanged="Colors_SelectedIndexChanged" AppendDataBoundItems="True" DataSourceID="LinqDataSource3" DataTextField="color" DataValueField="color" >
<asp:ListItem Text="" Value=""></asp:ListItem>
</asp:DropDownList>
<asp:DropDownList ID="Size" runat="server" OnSelectedIndexChanged="Size_SelectedIndexChanged" AppendDataBoundItems="true" AutoPostBack="true" CssClass="form-control detal-page-input" Style="height: 30px;" DataSourceID="LinqDataSource2" DataTextField="size" DataValueField="size" EnableViewState="true">
<asp:ListItem Text="" Value=""></asp:ListItem>
</asp:DropDownList>
<asp:TextBox Name="txtKolicina" ID="txtKolicina" runat="server" CssClass="form-control form-numberone detal-page-input" OnTextChanged="txtKolicina_TextChanged" ></asp:TextBox>
this is backEnd
protected void Size_SelectedIndexChanged(object sender, EventArgs e)
{
//do something
}
protected void Colors_SelectedIndexChanged(object sender, EventArgs e)
{
//do something
}
protected void txtKolicina_TextChanged(object sender, EventArgs e)
{
//do something
}
UPDATE
public string[] GetColor()
{
CMS_Shop_ModuleDataContext db = new CMS_Shop_ModuleDataContext();
var color = (from p in db.CMS_Articles
where
p.articleID == int.Parse(HiddenFieldArticalId.Value) ||
p.sameAsArticleID == int.Parse(HiddenFieldArticalId.Value)
//where p.articleID == 10049 || p.sameAsArticleID == 10049
select p.color).Distinct();
return color.ToArray();
}
public int GetColorCount()
{
CMS_Shop_ModuleDataContext db = new CMS_Shop_ModuleDataContext();
var color = (from p in db.CMS_Articles
where (p.articleID == int.Parse(HiddenFieldArticalId.Value)
|| p.sameAsArticleID == int.Parse(HiddenFieldArticalId.Value))
&& p.color != ""
select p.color);
return color.Distinct().Count();
}
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
if (GetColorCount() == 0)
{
Colors.Visible = false;
lblBoja.Visible = false;
}
else
{
Colors.Visible = true;
lblBoja.Visible = true;
}

Answer 1

Looks like you use View State and repopulate your DropDownLists in code behind on Postback. Can you show OnInit and OnLoad ?
Or just try this code:
if (!IsPostBack) {
// populate all drop downs lists
}

Answer 2

Ok i found what was the problem.
a change
EnableViewState="false"
to
EnableViewState="true"