Re: [Help-smalltalk] How to use trees with OrderedCollections etc

[Stefan Schmiedl]

On Tue, 10 Nov 2009 08:46:10 +0200
Bèrto ëd Sèra <address@hidden> wrote:

> Hi all,
> 
> one more stupid question. I've been building a UI mockup happily
> quoting the sample that reads
> 
>       tree := (Iliad.Tree new)
>                  item: Object;
>                  childrenBlock: [:class | class subclasses];
>                  contentsBlock: [:e :class | e text: class name]

I guess the main problem is that the above combination of Object and
#subclasses leads to a tree of objects implementing the message #subclasses,
while you have a collection (responding to #contents) and symbols (not
responding to #contents).

One way to get around this is to wrap your different objects into a thin
decorator providing a common interface, so that the following would work:

tree := (Iliad.Tree new)
           item: myTreeViewableCollectionOfLocalizableSymbols
           childrenBlock: [:item | item children ]
           contentsBlock: [:e :item | e text: item displayString ]

I apologize for that looong name :-)

Object subclass: TreeNodeHolder [
  | model getter |
  class [
    on: anObject getter: aBlock [
      ^ self basicNew model: anObject; getter: aBlock; yourself
    ]
  ]
  children [ ^ getter value: model ]
]

treeModel := TreeNodeHolder
               on: myTVCOLS 
               getter: [:coll | coll collect: [:elt | 
                          TreeNodeHolder on: elt getter: [:sym | 
OrderedCollection new ]
                       ].
tree := (Iliad.Tree new)
           item: treeModel
           childrenBlock: [:item | item children ]
           contentsBlock: [:e :item | e text: item displayString ]

Mind you, this snippet was written with dangerously low blood sugar levels,
so beware :-)

You can also avoid a lot of the uglyness if your application classes implement
a consistent interface for this purpose from the start.

HTH
s.