Multiselect Blank Values

[Jeff]

I have a multi-select Visible report parameter with AllowBlank set to True. When the user de-selects all values in the multi-select, they get a validation error indicating that the parameter is required. Why is this?

Note, if I select AllowNull for the parameter, I get a "NULL" checkbox next to the parameter in the UI, which looks completely ridiculous. I don't want to set it to NULL, I just want to not select any values...

How can I fix this?

[Peter]

Hello Jeff,

The Report Parameter area provides out of the box UI support for the parameters that covers most of the user cases and for that reason it is not highly customizable. Keep in mind however that the NULL text may be changed to some more appropriate term from your application domain (see Report Viewer Localization).

If still that does not fit your UI requirement, you should create custom UI for the parameters (for example using our Controls) and hook it up to the parameters via the Reporting API as shown in the following code snippet: 

protected void Page_Load(object sender, EventArgs e)
{
    var instanceReportSource = new InstanceReportSource
    {
        ReportDocument = new Invoice()
    };
    instanceReportSource.Parameters.Add("MultiValueParameter", new object[] { 1, 2 });
    instanceReportSource.Parameters.Add("SingleValueParameter", "my value");
    ReportViewer1.ReportSource = instanceReportSource;
}

Protected Sub Page_Load(sender As Object, e As EventArgs)
    Dim instanceReportSource = New InstanceReportSource() With { _
        .ReportDocument = New Invoice() _
    }
    instanceReportSource.Parameters.Add("MultiValueParameter", New Object() {1, 2})
    instanceReportSource.Parameters.Add("SingleValueParameter", "my value")
    ReportViewer1.ReportSource = instanceReportSource
End Sub

Regards,
Peter
the Telerik team