I am trying to disable the disable the button on filefield at runtime from viewcontroller but I am getting the error.

**Error in Component.js** 

me.ariaEl.dom.setAttribute('aria-disabled', false); // Cannot read property 'setAttribute' of null [ Seems me.ariaEl.domis coming as null]

**Error stack trace .........**

```
Uncaught TypeError: Cannot read property 'setAttribute' of null
at constructor.onEnable (Component.js?version=20170809094755:4378)
at constructor.callParent (Base.js?version=20170809094755:1288)
at constructor.onEnable (Button.js?version=20170809094755:1786)
at constructor.callParent (Base.js?version=20170809094755:1288)
at constructor.onEnable (FileButton.js?version=20170809094755:165)
at constructor.enable (Component.js?version=20170809094755:3033)
at constructor.setDisabled (Component.js?version=20170809094755:4863)

```

I have a simple file field,

```
           {
                xtype: 'filefield',
                fieldLabel: 'Attach Items',
                buttonText: 'Browse Items',
                itemId : 'buttonid',
                buttonConfig: {
                    id : 'uploadmailwidget0Btn'

                },
           }

```

Trying to disable in viewcontroller as -
Code:

```
 Ext.getCmp('uploadmailwidget0Btn').setDisabled(true);

```

Can someone please help? Ask is simple, I want to disable the button on filefield from viewcontroller.