How to Change the Dropdown list Values

Hi @NageswaraRaoAddanki60 

Hope you are looking for the below solution

If I'm understanding correctly, you 2 dropdown fields, and when you change 1st DropDown value, and based on that you wanted to load the 2nd DropDown values.

 DropDown1
 DropDown2

protected virtual void DAC1_DropDown1_FieldSelecting(PXCache cache, PXFieldSelectingEventArgs e)
        {
            DAC1 row = e.Row as DAC1;
            if (row != null)
            {
                var allowedValues = new List<string>();
                var allowedLabels = new List<string>();
                foreach (INSite site in PXSelect<INSite, Where<INSite.siteID, IsNotNull, And<INSite.siteID, NotEqual<SiteAttribute.transitSiteID>, And<Match<Current<AccessInfo.userName>>>>>>.Select(this))
                {
                    allowedValues.Add(site.SiteID.ToString());
                    allowedLabels.Add(site.SiteCD.Trim());
                }
                e.ReturnState = PXStringState.CreateInstance(e.ReturnState, 500, true, typeof(DAC1.DropDown1).Name, false, -1, string.Empty, allowedValues.ToArray(), allowedLabels.ToArray(), false, null);              
            }
        } 

        // In the Below field selecting you need to add a condition load the values based on the 1st dropdown

protected virtual void DAC1_DropDown2_FieldSelecting(PXCache cache, PXFieldSelectingEventArgs e)
        {
            DAC1 row = e.Row as DAC1;
            if (row != null)
            {
                var allowedValues = new List<string>();
                var allowedLabels = new List<string>();
                foreach (INSite site in PXSelect<INSite, Where<INSite.siteID, IsNotNull, And<INSite.siteID, NotEqual<SiteAttribute.transitSiteID>, 
				And<Match<Current<AccessInfo.userName>>,
				And<Insite.Field1,Equal<Required<Insite.Field1>>>>>>>.Select(this, row.DropDown1)) 
                {
                    allowedValues.Add(site.SiteID.ToString());
                    allowedLabels.Add(site.SiteCD.Trim());
                }
                e.ReturnState = PXStringState.CreateInstance(e.ReturnState, 500, true, typeof(DAC1.DropDown2).Name, false, -1, string.Empty, allowedValues.ToArray(), allowedLabels.ToArray(), false, null);              
            }
        }

Also add one more EVENT to invoke the 2nd Dropdown fieldSelecting event when we change the 1st dropdown
 

protected virtual void DAC1_DropDown1_FieldUpdated(PXCache cache, PXFieldUpdatedEventArgs e)
        {
            DAC1 row = e.Row as DAC1;
            if (row != null)
            {
				ref Val  = row.Dropdown1;
				//The below code will invoke the 2nd DropDown field selecting event to load the values based on the 1st DropDown1
                sender.RaiseFieldSelecting<SOLine.shipDate>(row, ref Validate, true);
			}
		}

Hi @praveenpo , @Naveen Boga In this way I tried. but, couldn't get. 
here dropdown 1 values are fixed , no need to change the these value.

 protected virtual void SSPSetupActive_ValidFor_FieldSelecting(PXCache cache, PXFieldSelectingEventArgs e)

        {

            SSPSetupActive row = e.Row as SSPSetupActive;

            var allowedValues = new List<string>();

            var allowedLabels = new List<string>();

            if (row != null)

            {

                if (row.Feature == "Inspect")

                {

                    allowedValues.Add(SSS.SSP.Helper.Constant.ServiceOrder.ToString());

                    allowedLabels.Add(SSS.SSP.Helper.Messages.ServiceOrder.Trim());

                }

                e.ReturnState = PXStringState.CreateInstance(e.ReturnState, 500, false, typeof(SSPSetupActive.validFor).Name, false, -1, string.Empty, allowedValues.ToArray(), allowedLabels.ToArray(), false, null);

            }

        }

Thank you for your support.

Yes, @praveenpo ValidFor field commitchanges=true

<px:PXGridColumn  Type="DropDownList" CommitChanges="True" DataField="ValidFor" Width="70" ></px:PXGridColumn>