Python add-in: pass selected layer of combo box to a button

I want to list layer names in a combo box and pass the selected layer name to onclick of a button.
I could list the layer names in combobox but i don’t know how to pass the name to a button. How can i solve the issue?

import arcpy
import pythonaddins

class ButtonClass2(object):
    """Implementation for test_addin.button (Button)"""
    def __init__(self):
        self.enabled = True
        self.checked = False
    def onClick(self):
            
        pass
        

class ComboBoxClass1(object):
    """Implementation for test_addin.combobox (ComboBox)"""
    def __init__(self):
        self.items = ["item1", "item2"]
        self.editable = True
        self.enabled = True
        self.dropdownWidth = 'WWWWWW'
        self.width = 'WWWWWW'
    def onSelChange(self, selection):
        pass
    def onEditChange(self, text):
        pass
    def onFocus(self, focused):
         # When the combo box has focus, update the combo box with the list of layer names.
    if focused:
        self.mxd = arcpy.mapping.MapDocument('current')
        layers = arcpy.mapping.ListLayers(self.mxd)
        self.items = []
        for layer in layers:
            self.items.append(layer.name)
    def onEnter(self):
        pass
    def refresh(self):
        pass