A custom view class instance is not a view by itself. This means that you cannot cast a view to a custom view class.
You can use a custom type to store all the information needed.
1. Add to class_globals
B4X:
Type AutoTextSizeLabelTag (Name As String, Instance As AutoTextSizeLabel)
2. Add to DesignerCreateView:
B4X:
Dim tag As AutoTextSizeLabelTag
tag.Initialize
tag.Name = Base.Tag
tag.Instance = Me
lbl.Tag = tag
3. Add to activity code:
B4X:
Sub GetAutoTextSizeLabelFromTag(tag As String) As AutoTextSizeLabel
Dim res As AutoTextSizeLabel
For Each v As View In Activity.GetAllViewsRecursive
If v.Tag Is AutoTextSizeLabelTag Then
Dim atag As AutoTextSizeLabelTag = v.Tag
If atag.Name = tag Then Return atag.Instance
End If
Next
Return res
End Sub