Accessing the RenderingContext.Current.Rendering.Item on controller in Sitecore 9 [duplicate]

Question

I'm trying to get the current item for filter search value. When im trying to access the RenderingContext.Current.Rendering.Item it showing some kind of error. Please find my screen shot below. 1. I'm Getting error because of postback in case if it is, How to resolve this without ajax?

Error Message:

System.InvalidOperationException
  HResult=0x80131509
  Message=Attempt to retrieve context object of type 'Sitecore.Mvc.Presentation.RenderingContext' from empty stack.
  Source=Sitecore.Mvc
  StackTrace:
   at Sitecore.Mvc.Common.ContextService.Peek[T]()
   at Molina.Project.Microsites.Web.Controllers.MicroSites.HopeLocationDropOff.LocationDropOffController.GetLocationInfo(String SearchString) in C:\Molina\Mohamed\Project\Microsites\Molina.Project.Microsites.Web\Controllers\MicroSites\HopeLocationDropOff\LocationDropOffController.cs:line 23
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c.<BeginInvokeSynchronousActionMethod>b__9_0(IAsyncResult asyncResult, ActionInvocation innerInvokeState)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`2.CallEndDelegate(IAsyncResult asyncResult)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<InvokeActionMethodFilterAsynchronouslyRecursive>b__11_0()
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_1.<InvokeActionMethodFilterAsynchronouslyRecursive>b__2()