Refresh Generic List in ASP.NET after page is postback or refreshed
<p>I have other trouble and I cannot solve it.</p>

<p>In ASP.NET I have DropDownList object which takes data from a Generic List. In ASP.NET page</p>

<pre><code>&lt;tr&gt;&lt;td&gt;Choose category&lt;/td&gt;
&lt;td&gt;&lt;asp:DropDownList id="list_categories" runat="server"&gt;&lt;/asp:DropDownList&gt;&lt;/td&gt;
&lt;td&gt;
&lt;asp:RequiredFieldValidator ControlToValidate="list_categories" runat="server" Display="Static" ErrorMessage="Select category" ID="verify_category" ValidationGroup="add_link_group"&gt;
&lt;/asp:RequiredFieldValidator&gt;&lt;/td&gt;&lt;/tr&gt;
</code></pre>

<p>and the behind code :</p>

<pre><code>private void generate_select( DropDownList select ) {

         BusinessLayerArcht layer = LoadDataFromBL();

         foreach ( CategoriesCtrlDto cto in layer.Categories ) {          
            select.Items.Add( cto.Name );
         }
      }
</code></pre>

<p>and the Page_Load</p>

<pre><code>generate_select( list_categories );
</code></pre>

<p>I tried with Clear() but when I added a new link to a selected category , it will be inserted at first category
If I don't call .Clear() function then the inseration it's ok but after page refreshing, the list contains duplicate categories</p>

<p>Initial I had
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<p>after inserting a new link or other event which refresh page, the list will shows as :
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<p>If I refresh four times the page then the list has 
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<p>Repeats four times, so it duplciates at each page postback or refresh.
I tried also to clear cache if <code>(Page.isPostBack)</code></p>
