[SalesForce] Using a Map type attribute in aura:if

UPDATE

I believe this is a bug. If you do not default your Map to empty object default="{}", then lightning appears to not register the existence of the Map declared in the markup.

So, the fix is simple - change your attribute definition to this:

<aura:attribute name="FilesNameMap" type="Map" default="{}"/>

PREVIOUS

You have a typo. In your attribute definition, you have called the Map FilesNameMap but in your getter you have called it FilesObjectMap.

Which means it's going to be null when you try to set something to it.

You can't. I've asked the same question a while ago in a map context:

Using a Map type attribute in aura:if

What you could do though is use an aura:iteration to run over the array, and inside render components with an index/value variable to be passed from the iteration, and have the component do the logic inside based on the index/value passed.

Iteration:

<aura:iteration items="{!v.myarray}" var="someVar" indexVar="someIndex" >
  <c:someComponent aValue="{!someVar}" anIndex="{!someIndex}" />
</aura:iteration>

Inner component:

<aura:component>
  <aura:attribute name="aValue" type="String" />
  <aura:attribute name="anIndex" type="Integer" />
  <div>
    {!v.aValue}
    {!v.anIndex}
  </div>
</aura:component>

Alternatively, you could read the array in an init/change event and set the result in an attribute:

Markup:

<aura:component>
    <aura:attribute name="myArray" type="Object" />
    <aura:attribute name="index" type="Integer" default="0" />
    <aura:attribute name="value" type="String" />
    <aura:handler name="change" value="{!v.index}" action={!c.accessArray}" />
    ...

    {!v.value}
</aura:component>

Controller:

accessArray : function(component) {
    var myArray = component.get('v.myArray');
    var index = component.get('v.index');
    component.set('v.value', myArray[index]);
}