DropDownList and Update Panel
I develop address control, which contains 2 DropDownLists (for cities and countries) and several TextBoxes. The second DropDownList DataSource depends on the first DropDownList DataSource.
<fieldset>
<legend><%=Title%></legend>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<div>
<label for="<%=ddlCountry.ClientID %>">Country</label>
开发者_StackOverflow中文版 <asp:DropDownList runat="server" ID="ddlCountry"
DataTextField="Name" DataValueField="Id"
DataSource="<%#Facade.Addresses.GetCountries() %>"
AutoPostBack="true"
OnSelectedIndexChanged="ddlCountry_SelectedIndexChanged"
/>
</div>
<div>
<label for="<%=ddlCity.ClientID %>">City</label>
<asp:DropDownList runat="server" ID="ddlCity"
DataTextField="Name" DataValueField="Name" />
</div>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="ddlCountry" EventName="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel>
<div>
<label for="<%=txtStreet.ClientID %>">Street</label>
<uc:TextBox ID="txtStreet" Text="<%#Address.Street %>" runat="server" />
</div>
<div>
<label for="<%=txtBlock.ClientID %>">Block</label>
<uc:TextBox ID="txtBlock" Text="<%#Address.Block %>" runat="server" />
</div>
<div>
</fieldset>
Code Behind
protected void Page_Init(object sender, EventArgs e)
{
ddlCountry.DataBind();
if (!IsPostBack)
{
ddlCity.DataSource = Facade.Addresses.GetCities(countryId);
ddlCity.DataBind();
}
}
protected void ddlCountry_SelectedIndexChanged(object sender, EventArgs e)
{
ddlCity.DataSource = Facade.Addresses.GetCities(countryId);
ddlCity.DataBind();
}
It works good. But if other control on the page causes PostBack, when the SelectedValue in ddlCity sets to the first (default) value.
How do I avoid it?
Move the code on Page_Init
to Page_Load
and put it inside !IsPostBack
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
ddlCountry.DataBind();
ddlCity.DataSource = Facade.Addresses.GetCities(countryId);
ddlCity.DataBind();
}
}
put ddlCountry.DataBind(); inside if condition
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