which event to be fired for check box check

[bee]

Hi I have check box and when I checked it. I want to get message box, , but I am not able to guess which event to be used. in extjs 3.3.1 I used check event
I tried activate event, but it doesn't work I am using extjs 4.0.7
My checkbox definition is :

{
xtype : 'checkboxfield',
fieldLabel : 'Label',
id : 'chkid',
labelSeparator : '',
labelWidth : 80,
boxLabel : '',
ref: 'chkid',
name : 'chkid',
anchor : '100%'
}

and my event call is as below :

Ext.getCmp('chkid').on('activate', function(){    
    if (this.checked) {
        console.log('testing');
    }  
});

[tvanzoelen]

it is 'change' in ExtJs 4

[bee]

This is fixed by change event. Thanks a Mill.