How to Prevent Users from Creating Empty POs in Dynamics 365 Finance and Supply Chain

[FormControlEventHandler(formControlStr(PurchTable, TabPageDetails), FormControlEventType::AllowPageDeactivate)]
public static void TabPageDetails_AllowPageDeactivate(FormControl sender, FormControlEventArgs e)
{
 
    // Cast sender to FormTabControl
    FormTabControl tabControl = sender as FormTabControl;

    // Use known tab page control names to check visibility
    FormRun formRun = sender.formRun();
    FormControl tabPageDetails = formRun.design().controlName(formControlStr(PurchTable, TabPageDetails));

    if (tabPageDetails.visible())
    {
        FormDataSource purchLineDS = formRun.dataSource(formDataSourceStr(PurchTable, PurchLine));
        PurchLine purchLineRecord = purchLineDS.getFirst();

        if (!purchLineRecord)
        {
            // Get the PurchTable datasource
            FormDataSource purchTableDS = formRun.dataSource(formDataSourceStr(PurchTable, PurchTable));
       
            PurchTable purchTable = purchTableDS.cursor() as PurchTable;
           
            // Show a confirmation dialog
            if (Box::yesNo("This PO has no lines. Delete it?", DialogButton::No) == DialogButton::Yes)
            {
                ttsBegin;
                purchTable.delete();
                ttsCommit;

                // Refresh the datasource to reflect the deletion
                purchTableDS.research(true);
            }

        }
    }
}// Another possibility is to hook into tab change event.
  [FormControlEventHandler(
      formControlStr(PurchTable, MainTab),
      FormControlEventType::TabChanged)]
  public static void MainTab_OnTabChanged(FormControl sender, FormControlEventArgs e)
  {
      FormRun formRun = sender ? sender.formRun() : null;
      if (!formRun)
          return;

      // Optional: if the form was opened via deep link (no caller), do nothing.
      // TabChanged normally doesn't fire on initial load, but this avoids edge cases.
      Args a = formRun.args();
      // if (!a || !a.caller()) return;

      FormTabControl tab = sender as FormTabControl;
      FormTabControlTabChangedEventArgs tce = e as FormTabControlTabChangedEventArgs;
      if (!tab || !tce)
          return;
     
      // Resolve the Details page control
      FormTabPageControl detailsPage =
          formRun.design().controlName(formControlStr(PurchTable, TabPageDetails)) as FormTabPageControl;
      if (!detailsPage)
          return;
     
      // oldTab/newTab are INDEXES, not control IDs
      int oldIdx = tce.oldTab();

      // Map index -> page control
      FormTabPageControl oldPage = tab.controlNum(oldIdx) as FormTabPageControl;

      // Only when LEAVING the Details page back to the grid view
      if (oldPage && oldPage.id() == detailsPage.id())
      {
          FormDataSource purchTableDS = formRun.dataSource(formDataSourceStr(PurchTable, PurchTable));
          FormDataSource purchLineDS  = formRun.dataSource(formDataSourceStr(PurchTable, PurchLine));

          PurchTable purchTable = purchTableDS ? (purchTableDS.cursor() as PurchTable) : null;
          PurchLine  lineFirst  = purchLineDS ? purchLineDS.getFirst() : null;

          if (purchTable && !lineFirst && !PurchLine::exist(purchTable.PurchId))
          {
         if (Box::yesNo("This PO has no lines. Delete it?", DialogButton::No) == DialogButton::Yes)
              {
                  ttsBegin;
                  purchTable.delete();
                  ttsCommit;

                  purchTableDS.research(true);
              }
          }
      }
  }