how to get the input value in dialog which create by xmlfragment in fiori

Dear friends,

     I used this code in my controller to create a dialog though xmlfragment, now I want to get the input value in the dialog how do I make it ? I try to use the same way to get the value just like this in my controller,but it didn't work.

var iordering = this.getView().byId("ApprovalInput");

SearchHelp: function() {

  if (!this._oViewsearchDialog) {

  this._oViewsearchDialog = sap.ui.xmlfragment("Demo.view.SearchHelpDialog", this);

  this.getView().addDependent(this._oViewsearchDialog);

  this._oViewsearchDialog.addStyleClass(this.getOwnerComponent().getContentDensityClass());

  }

  this._oViewsearchDialog.open();

  },

some of my xmlfragment code:

<Label design="Bold" id="VSDThemeLabel" text="Approval Status"/>

  <Input id="ApprovalInput" placeholder="Enter Product ..." showSuggestion="true" suggestionItems="{/PurchaseOrderCollection}" type="Text">

  <suggestionItems>

  <core:Item text="{ApprovalStatus}"/>

  </suggestionItems>

  </Input>

Thanks for your sincerely answer!

Zhang