I used lightning:select like this:
<lightning:select label="op:" aura:id="opid" name="fop"
onchange="{!c.onchangeev}"
disabled="{!v.dis}" required="true">
<option selected="" value="">--Select operator--</option>
<aura:iteration items="{!v.oplist}" var="item" indexVar="key">
option value="{!item.key}">{!item.value}</option>
</aura:iteration>
</lightning:select>
My issue: on change event is fired after i select option after second time. Anyone have idea why?