CODEWITHSUNDEEP
c#asp.netdrop-down-menu
Justen
Justen

Reputation: 4869

Best way to check if a drop down list contains a value?

When the user navigates to a new page, this ddl's selected index is determined by a cookie, but if the ddl doesn't contain that cookie's value, then I'd like it to be set the 0. What method would I use for the ddl? Is a loop the best way, or is there a simply if statement I can perform?

This is what I've attempted, but it doesn't return a bool.

if ( !ddlCustomerNumber.Items.FindByText( GetCustomerNumberCookie().ToString() ) )
    ddlCustomerNumber.SelectedIndex = 0;

Upvotes: 67

Views: 185838

Answers (10)

estinamir
estinamir

Reputation: 503

Sometimes the value needs to be trimmed of whitespace or it won't be matched, in such case this additional step can be used (source):

if(((DropDownList) myControl1).Items.Cast<ListItem>().Select(i => i.Value.Trim() == ctrl.value.Trim()).FirstOrDefault() != null){}

Upvotes: 0

Mia Zhang
Mia Zhang

Reputation: 1

If the function return Nothing, you can try this below

if (ddlCustomerNumber.Items.FindByText(
    GetCustomerNumberCookie().ToString()) != Nothing)
{
...
}

Upvotes: 0

Vijaya Krishna Tummala
Vijaya Krishna Tummala

Reputation: 11

ListItem item = ddlComputedliat1.Items.FindByText("Amt D");
if (item == null) {
    ddlComputedliat1.Items.Insert(1, lblnewamountamt.Text);
}

Upvotes: 1

Alejandro Haro
Alejandro Haro

Reputation: 1394

//you can use the ? operator instead of if

ddlCustomerNumber.SelectedValue = ddlType.Items.FindByValue(GetCustomerNumberCookie().ToString()) != null ? GetCustomerNumberCookie().ToString() : "0";

Upvotes: 0

Tobias
Tobias

Reputation: 2139

If 0 is your default value, you can just use a simple assignment:

ddlCustomerNumber.SelectedValue = GetCustomerNumberCookie().ToString();

This automatically selects the proper list item, if the DDL contains the value of the cookie. If it doesn't contain it, this call won't change the selection, so it stays at the default selection. If the latter one is the same as value 0, then it's the perfect solution for you.

I use this mechanism quite a lot and find it very handy.

Upvotes: 5

Nathan
Nathan

Reputation: 2775

On C# this works:

        if (DDLAlmacen.Items.Count > 0)
        {
            if (DDLAlmacen.Items.FindByValue("AlmacenDefectoAndes").Value == "AlmacenDefectoAndes")
            {
                DDLAlmacen.SelectedValue = "AlmacenDefectoAndes";
            }
        }

Update:

Translating the code above to Visual Basic doesn't work. It throws "System.NullReferenceException: Object reference not set to an instance of an object.."

So. for this to work on Visual Basic, I had to change the code like this:

        If DDLAlmacen.Items.Count > 0 Then
            If DDLAlmacen.Items.Contains(New ListItem("AlmacenDefectoAndes")) Then
                DDLAlmacen.SelectedValue = "AlmacenDefectoAndes"
            End If
        End If

Upvotes: 1

Andy Rose
Andy Rose

Reputation: 16984

You could try checking to see if this method returns a null: 

if (ddlCustomerNumber.Items.FindByText(GetCustomerNumberCookie().ToString()) != null)
    ddlCustomerNumber.SelectedIndex = 0;

Upvotes: 0

Scott Arrington
Scott Arrington

Reputation: 12503

There are two methods that come to mind:

You could use Contains like so:

if (ddlCustomerNumber.Items.Contains(new 
    ListItem(GetCustomerNumberCookie().ToString())))
{
    // ... code here
}

or modifying your current strategy:

if (ddlCustomerNumber.Items.FindByText(
    GetCustomerNumberCookie().ToString()) != null)
{
    // ... code here
}

EDIT: There's also a DropDownList.Items.FindByValue that works the same way as FindByText, except it searches based on values instead.

Upvotes: 142

Rubens Farias
Rubens Farias

Reputation: 57956

What about this:

ListItem match = ddlCustomerNumber.Items.FindByText(
    GetCustomerNumberCookie().ToString());
if (match == null)
    ddlCustomerNumber.SelectedIndex = 0;
//else
//    match.Selected = true; // you'll probably select that cookie value

Upvotes: 1

Nathan Wheeler
Nathan Wheeler

Reputation: 5932

That will return an item. Simply change to:

if (ddlCustomerNumber.Items.FindByText( GetCustomerNumberCookie().ToString()) != null)
    ddlCustomerNumber.SelectedIndex = 0;

Upvotes: 9

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