[Zope-CMF] Re: Working with Zope 3 skin layers

[Philipp von Weitershausen]

Charlie Clark wrote:
> What I think is still confusing me is:
> 1) I have created my dedicated skin
> 2) I have registered a view for that skin
> 
> I assumed that by registering the view for the skin, the view would 
> automatically use the right layer when called.

Views don't "use" layers. You apply a skin layer to the request, and 
depending on whether the view was registered for this skin layer or any 
of the layers that are contained in that skin layer, the view will be found.

> The effect being much the same as a customised view in a CMF layer:
> higher up the chain takes precedence.

Zope 3 layers and skins work exactly like that.

> But it seems that this is not the case: unless it is set 
> otherwise Zope will use the default skin.

Sure, but that's just like in the CMF where you tell the portal_skins 
tool which skin is the default.

> Is it possible to get individual views to use different skins without using ++skin++ in the URL?

That doesn't make any sense to me and it's not how the CMF works either. 
In the CMF you may put different views in different skin layers (i.e. 
folders), but then you always combine them to a skin (in "Properties" 
page of the portal_skins tool where you enter a list of folders that 
make up the skin). For instance, you may have the following skin 
definition there:

Default = custom
           something_else
           cmf_default

This is very similar to Zope 3, except that we now have interfaces, e.g. 
ICMFDefaultSkin, ISomethingElse and IMyCustomLayer. You'd now register 
views for those layer interfaces (probably just for IMyCustomLayer) and 
then combine those layer interfaces in a skin interface, which is then 
given a name using the <interface /> directive and then registered as 
the default skin:

class IMySkin(ICustom, ISomethingElse, ICMFDefaultSkin):
     pass


<interface interface="...IMyDefaultSkin"
            type="zope.publisher.interfaces.browser.IBrowserSkinType"
            name="MySkin"
            />

<browser:defaultSkin name="MySkin" />

>>> Regarding CMFDefault - all views are registered explicitly for 
>>> ICMFDefaultSkin but I think this isn't necessary as this is 
>>> configured as the default skin.
>>
>> No, it *is* necessary, because the default skin can always change. In 
>> fact, nearly every application (in the Zope 3 world) sets the default 
>> skin (otherwise you'd need those hideous ++skin++ things in all URLs).
>>
>> Also, by explicitly putting all views on the ICMFDefaultSkin layer, 
>> those views are only there if your skin interface inherits from 
>> ICMFDefaultSkin. Which means you can easily "switch off" those CMF 
>> views by not including ICMFDefaultSkin. For some people this is an 
>> important use case.
> 
> 
> Wouldn't that raise an error on startup if ICMFDefaultSkin isn't found? 

Uh, it's an interface... how can it not be found?

> Or how do you "not include" ICMFDefaultSkin? Using overrides?

By having your skin interface not inherit from ICMFDefaultSkin, just 
like in the CMF where you would remove the cmf_default layer from the 
skin definition if you didn't want to have the views from cmf_default 
available.

> PS: in your book the appendix to ZCML browser:defaultSkin says "see 
> browser:skin". This has been deprecated, I think.

Ah, thank you!