Cascading DropDownList on GridView

Cascading DropDownLists on GridView

Cascading DropDownLists on GridView


In this Blog, we will learn how to get the current Row of GridView inside the SelectedIndexChanged Event of a DropDownList present on the GridView itself and then find the other DropDownList and bind that.

Background

The requirement came up in one of my projects to Bind one DropDownList present on a Column based on the selection of DropDownList present on another Column. So, it was like the Cascading DropDownLists, where both the DropDownLists are present on the same GridView.

So, steps to get the solution would be like…

  1. Attach the SelectedIndexChanged Event for the first DropDownList on GridView
  2. Inside the Event, first get the GridView Row, from which the first DropDownList is selected
  3. Then from the current GridView Row, find the second DropDownList and bind it with a DataTable or something

The step which is bold is very important. Let’s go step by step.

GridView Markup

In the Markup, you can see that I have two DropDownLists Declared inside the GridView. One is for Country and another one for City. Just for demo purpose, I have hard coded the Items for Country. You can dynamically populate that using code.

Note: According to Step – 1, I have attached the OnSelectedIndexChanged Event to the Country DropDownList.
Goal: Our goal is to populate the City DropDownList for the particular row, when Country is selected in that row.

<asp:GridView ID="gvWithCascadingDropDownList" runat="server" AutoGenerateColumns="false">
	<Columns>
		<asp:BoundField DataField="RowNumber" />
		<asp:TemplateField HeaderText="Country">
			<ItemTemplate>
				<asp:DropDownList 
                        ID="ddlCountry" runat="server" 
                        AutoPostBack="true" 
                        OnSelectedIndexChanged="ddlCountry_SelectedIndexChanged">
					<asp:ListItem Text="-1">Select Country</asp:ListItem>
					<asp:ListItem Text="India">India</asp:ListItem>
					<asp:ListItem Text="Nepal">Nepal</asp:ListItem>
					<asp:ListItem Text="Bangladesh">Bangladesh</asp:ListItem>
					<asp:ListItem Text="Sri lanka">Sri lanka</asp:ListItem>
				</asp:DropDownList>
			</ItemTemplate>
		</asp:TemplateField>
		<asp:TemplateField HeaderText="City">
			<ItemTemplate>
				<asp:DropDownList ID="ddlCity" runat="server">
				</asp:DropDownList>
			</ItemTemplate>
		</asp:TemplateField>
	</Columns>
</asp:GridView>

What’s Next?

Let’s write code inside the Country Change Event and populate the City DropDownList.
So, according to the Step – 2

Inside the Event, first get the GridView Row, from which the first DropDownList is selected

For the above, we have to get the current Country DropDownList first, which we can easily get by.

// Get the Country DropDownList first.
DropDownList ddlCountry = (DropDownList)sender;

Now the important Step – 3.

Then from the current GridView Row, find the second DropDownList and bind it with a DataTable or something

In order to get the Containing Row for the DropDownList, we have to use the Control.NamingContainer Property.

The naming container for a given control is the parent control above it in the hierarchy that implements the INamingContainer interface. A server control that implements this interface creates a unique namespace for the ID property values of its child server controls. You can use the NamingContainer property of a naming container’s child control to get a reference to its parent container.

So, after getting the current GridView Row, now it is just a matter of finding the City DropDownList on that particular row and bind that with appropriate Data.

Below is the full code. I have used one Service to get the Cities Data. To use the Service, add Service Reference to your Project by right clicking on the Project in Visual Studio.

Service Reference Dialog

Service Reference Dialog


Service URL is – http://www.webservicex.net/globalweather.asmx?WSDL

protected void ddlCountry_SelectedIndexChanged(object sender, EventArgs e)
{
	// Get the Country DropDownList first.
	DropDownList ddlCountry = (DropDownList)sender;

	// Get the current GridView Row, from which the DropDownList is selected.
	GridViewRow currentRow = (GridViewRow)ddlCountry.NamingContainer;

	// Now let's find the City DropDownList on the same GridView Row.
	DropDownList ddlCity = (DropDownList)currentRow.FindControl("ddlCity");

	if (ddlCountry != null && ddlCountry.SelectedIndex > 0 && ddlCity != null)
	{
		string selectedCountry = ddlCountry.SelectedValue;

		// Get the Cities from the Service.
		string xmlCities = GetCitiesByCountry(selectedCountry);

		// Let's parse the XML into DataTable.
		XmlTextReader citiesReader = new XmlTextReader(new System.IO.StringReader(xmlCities));
		DataSet dsCities = new DataSet();
		dsCities.ReadXml(citiesReader);

		// Bind the City DropDownList.
		if (dsCities != null && dsCities.Tables.Count > 0 && dsCities.Tables[0].Rows.Count > 0)
		{
			ddlCity.DataSource = dsCities.Tables[0];
			ddlCity.DataTextField = "City";
			ddlCity.DataValueField = "City";
			ddlCity.DataBind();
		}
	}
	else if (ddlCity != null)
	{
		ddlCity.Items.Clear();
	}
}

private string GetCitiesByCountry(string selectedCountry)
{
	GlobalWeatherServiceReference.GlobalWeatherSoapClient client = new GlobalWeatherSoapClient();
	return client.GetCitiesByCountry(selectedCountry);
}

Hope You Enjoyed Reading

If you have any queries, please comment below. I will come back to you. Feel free to Like and Share the Blog in Social Sites.

Thanks for reading. 🙂

Why GridView RowUpdating Event is not giving the updated values?

Debugger Inside GridView RowUpdating Event

Debugger Inside GridView RowUpdating Event


This is a most common question in Forums. We will find the actual cause, for which the RowUpdating Event behaves abnormal.

Walk Through

  1. Add a GridView in aspx page and define all its required properties and Events.
    <asp:GridView ID="gvTestGrid" runat="server" AutoGenerateColumns="false" 
                  OnRowCancelingEdit="gvTestGrid_RowCancelingEdit"
                  OnRowEditing="gvTestGrid_RowEditing" 
                  OnRowUpdating="gvTestGrid_RowUpdating">
        <Columns>
            <asp:BoundField DataField="Column1" HeaderText="Some Column"/>
            <asp:CommandField ShowEditButton="true" />
        </Columns>
    </asp:GridView>
    
  2. Bind the GridView from back end. For our example, we will bind one DataTable.
    private void BindGrid()
    {
        // Add Column for the DataTable.
        DataTable dt = new DataTable();
        dt.Columns.Add(new DataColumn("Column1"));
    
        // Add Rows to DataTable.
        for (int i = 1; i < 5; i++)
        {
    	    DataRow dr = dt.NewRow();
    	    dr["Column1"] = "Old Value" + i;
    	    dt.Rows.Add(dr);
        }
    
        gvTestGrid.DataSource = dt;
        gvTestGrid.DataBind();
    }
  3. Define the GridView Events for Edit and Update operation.
    protected void gvTestGrid_RowEditing(object sender, GridViewEditEventArgs e)
    {
        //Set the edit index.
        gvTestGrid.EditIndex = e.NewEditIndex;
    
        //Bind data to the GridView control.
        BindGrid();
    }
    
    protected void gvTestGrid_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        //Get the new Values.
        GridViewRow row = gvTestGrid.Rows[e.RowIndex];
        string column1Value = ((TextBox)row.Cells[0].Controls[0]).Text;
    
        // Code to update the DataSource.
        //.....
    
        //Reset the edit index.
        gvTestGrid.EditIndex = -1;
    
        //Bind data to the GridView control.
        BindGrid();
    }
    
    protected void gvTestGrid_RowCancelingEdit(object sender, 
                                               GridViewCancelEditEventArgs e)
    {
        //Reset the edit index.
        gvTestGrid.EditIndex = -1;
    
        //Bind data to the GridView control.
        BindGrid();
    }
    
  4. GridView on Browser would look like…

    GridView on Browser

    GridView on Browser

    Now, Let’s Test

    To test the Edit and Update features, let’s click on Edit Button in any Row. We can see that GridView adds TextBoxes in all the cells of that Row immediately. It also shows you Update and Cancel Buttons where it was previously showing Edit Button.
    Let’s do some editing in the cells and click Update Button.

    GridView Cell Showing Updated Value

    GridView Cell Showing Updated Value


    It hits the breakpoint, we have set inside the RowUpdating Event. If we move our mouse on to the variables, which hold the cell values, we can see the old value instead of new updated value (Refer the debugging Screen Shot at the Top). So, we are stuck now, this is the bug.

    What to do now?

    Don’t panic. We need to find out what exactly in code is helping RowUpdating Event to give old values. So, the most wild guess is that, something is causing the Grid to bind again before RowUpdating Event, as we initially did during load.

    If you remember, in Step-2, we did bind the Grid, which is actually called on the Page Load like…

    protected void Page_Load(object sender, EventArgs e)
    {
        BindGrid();
    }
    

    According to the Event Life Cycle, when any Control Event is fired (here Grid RowUpdating), it first goes to Page Load. As it is coming to Page Load, so it calls the Bind method again and re-binds the Grid. Now, it goes to RowUpdating Event, but the updated values are lost because Grid is already reset in Page Load.

    So, How to Resolve?

    IsPostBack() is the answer. We have to check if the Page is posted back or not. If not, then we will bind the Grid.

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindGrid();
        }
    }
    

    Go and Share this with your friends

    This issue sometimes kills time. So, don’t wait, just share with everybody you know, who can understand this. Also provide your valuable feedback here. Thanks for reading.