sharepoint App Model: Not able to fetch the app part's custom properties

I have a provider hosted app for which I have created a clientwebpart item. In this clientWebPart I have added some custom properties:

<Content Type="html" Src="~remoteAppUrl/Pages/Default.aspx?strProp=_strProp_" />
<Properties>
  <Property
           Name="strProp"
           Type="string"
           RequiresDesignerPermission="true"
           DefaultValue="String default value"
           WebCategory="Basic app part category"
           WebDisplayName="A property of type string.">
  </Property>
</Properties>

But the problem is that on code behind file when I does below operation in page_Load() I always got NULL. Even thou I have remove {StandardToken} I am still getting the values of those

 string s = Request.QueryString["strProp"]; //always give null