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    <p>If I understood you right, you only need to change the value displayed in <code>dropDownListCity</code> according to the value selected in <code>dropDownListPostal</code>. To do so, you need to bind both dropdown lists in <code>Page_Load</code> and then handle the selected index when <code>SelectedIndexChanged</code> is triggered.</p> <pre><code>private IEnumerable&lt;KeyValuePair&lt;string, string&gt;&gt; GetData() { using(var dataContext = new DbEntities()) { return dataContext.VW_CustumAddress .ToList() .Select(item =&gt; new KeyValuePair&lt;string, string&gt;(item.Postal, item.City)) .ToArray(); } } protected void Page_Load(object sender, EventArgs e) { if(!IsPostback) { IEnumerable&lt;KeyValuePair&lt;string,string&gt;&gt; data = GetData(); //Bind Postal dropdown list dropDownListPostal.DataSource = data.Select(kvp =&gt; kvp.Key).ToList(); // ^ Select only 'Postal' column in dropdown list. dropDownListPostal.DataBind(); // Bind City dropdown list // We need to bind to a key-value pair to know the correspondence between items dropDownListCity.DataValueField = "Key"; dropDownListCity.DataTextField = "Value"; dropDownListCity.DataSource = data; dropDownListCity.DataBind(); } } </code></pre> <p>Now, after you bound your controls to data you only need to handle <code>SelectedIndexChanged</code> event of <code>dropDownListPostal</code> (don't forget to set <code>AutoPostback="true"</code> in the markup of <code>dropDownListPostal</code>). <strong>EDIT</strong>: Before selecting an item, clear the selection of your dropdown list to make sure only one item is selected.</p> <pre><code>protected void OnDropDownListPostalSelectedIndexChanged(object sender, EventArgs e) { dropDownListCity.ClearSelection(); var postal = dropDownListPostal.SelectedValue; var listItem = dropDownListCity.Items.FindByValue(postal); listItem.Selected = true; } </code></pre> <p>That should do it. Hope it helps.</p>
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    1. COThe soultion was great but i still have some errors, The first one is I cannot have multiplay data in a dropdown, i solved that by saying clearselection(); Now I can see all the City Names on the DropBoxCity but when i choose between others postalt, then the DropBoxCity Does not update and my the DropDownPostal just refresh and keep going back to the first value in dropdown index..
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    2. COthis is the error: Cannot have multiple items selected in a DropDownList
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    3. CO@SaiefAl-Faour, please see the latest edit - it should not give you the error with multiple selection.
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