Re: [platform-ui-dev] question about ITreeContentProvider

["jml" <jml@xxxxxxxx>]

Thank you Nick, you answered my question.

Maybe I should provide a wrapper for the DAG to get all the tree functions to work

jml

----- Original Message ----- 
From: "Nick Edgar" <Nick_Edgar@xxxxxxx>
To: <platform-ui-dev@xxxxxxxxxxx>
Sent: Thursday, October 17, 2002 9:34 PM
Subject: Re: [platform-ui-dev] question about ITreeContentProvider


> jml,
> 
> ITreeContentProvider.getParent(Object) is used to find the parent for the 
> given model element.  This is used when you ask the viewer to do something 
> to the element, but the viewer does not already know the element (tree 
> viewers are lazily populated, so there is no corresponding TreeItem yet). 
> Methods which use this include: reveal, setExpanded, expandToLevel, and 
> setSelection.
> 
> For example, in your tree structure below, if A had never been expanded, 
> then the viewer would not know about elements B or C.
> If you ask it to reveal(C), then it has to call getParent(C) to determine 
> which item(s) to expand and populate to show C.  In this case, your 
> content provider would return A, so the viewer would populate the children 
> of A, then expand A to reveal C.
> 
> Since you want to show a DAG, getParent can be one-to-many, so you can't 
> always answer this question (i.e. for B, as you point out).
> It's OK to always return null for getParent, as long as you steer clear of 
> using the methods above, or only use them on the elements that are known 
> to the tree.
> 
> Beware that having multiple equal elements in the tree can lead to other 
> confusnig behaviour, since the viewers typically assume a 1-1 mapping 
> between element and SWT item.
> For example, after expanding A and B if you ask the tree to select C, 
> which item should it select?  Currently it will select only the first one 
> found.
> 
> Hope this clarifies,
> Nick
> 
> 
> 
> 
> 
> "jml" <jml@xxxxxxxx>
> Sent by: platform-ui-dev-admin@xxxxxxxxxxx
> 10/17/02 03:08 AM
> Please respond to platform-ui-dev
> 
>  
>         To:     <platform-ui-dev@xxxxxxxxxxx>
>         cc: 
>         Subject:        [platform-ui-dev] question about ITreeContentProvider
> 
> 
> Hi, all
> 
> In ITreeContentProvider, there is a function as getParent(), is it 
> necessary?
> I have a data structure, which is a directed no-cycle graph.
> For example, it has A,B,C, and A->B, A->C and B->C
> 
> Now I want to show it as a tree, as
> 
> A
>  -B
>   -C
>  -C
> 
> and I want to just write a ITreeContentProvider to do that.
> 
> All other thing are very easy and straightforward, but the getParent(). 
> Since now when the parameter for getParent() is C, I don't know what to 
> return.
> 
> I tried just return null in getParent(), and the tree can be displayed. So 
> come my question, is getParent() necessary? Where does it be used in the 
> current system? Also, I would think the underlying TreeItem implementation 
> must already remember the parent relationship in it.
> 
> Thanks
> 
> jml
> 
> 
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