This code will cause it to update the size together with the form size:
B4X:
Sub Process_Globals
Private fx As JFX
Private MainForm As Form
Private HTMLEditor1 As HTMLEditor
Private wvEditor As WebView
End Sub
Sub AppStart (Form1 As Form, Args() As String)
MainForm = Form1
MainForm.Show
MainForm.RootPane.LoadLayout("1")
Dim jo As JavaObject = HTMLEditor1
wvEditor = jo.RunMethod("lookup", Array("WebView"))
End Sub
Sub MainForm_Resize (Width As Double, Height As Double)
wvEditor.SetSize(Width, Height)
End Sub