Infralution Support

[CNET Channel]

Hello!

I would like to refresh data in VirtualTree keeping expanded state of nodes. I mean, those nodes that were expanded before refresh would remain expanded(collapsed remain collapsed).
On refresh DataSource property of the tree is reassigned.
I might need to save expanded state of nodes somewhere before refresh operation and then restore it. But I could not find a way to find out whether a particular node is expanded or collapsed.

Could you help me with this problem?
Thanks.

[Infralution]

Rather than setting the DataSource again on refresh you might want to consider using the UpdateRows() method to force virtual tree to requery and rebuild the children for each row. This will maintain the expand state of the tree.

To do this it relies on being able to find the index of an item within its parents children using the IList.IndexOf(item) method. If you return the same actual items when the children are requeried this will work. If you create new items each time you return the children (ie there may be multiple objects representing the same item) then you need to ensure that you overload the item IsEqual and GetHashCode methods so that object representing the same item (aliases) are recognised as being the same object.

To answer your actual question you can find out whether a particular Row is expanded by its Expand state.
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Infralution Support

[CNET Channel]

Thanks!
Now I understand how it works inside.
The problem is solved.

I've got yet another issue.
Row class has method InsureVisible(). As I understand it should scroll the tree so that the row is visible. Is it right? Do I need to call any other function to refresh the tree after calling InsureVisible() on some row?

[Infralution]

[egl]

hello together,

we have the same problem that the tree collapses when we reload the data. we tried it by not setting the datasource again and use updaterows.
we got the data from a database and don't want to collaps the tree when we refresh the data. so if we don't want to set datasource again, that we have to merge the dataset. but this causes, data that was deleted between the two database calls stayed on the tree. so i tried it by cleaning the dataset before merging the new data back, but this collapsed the tree again. so i thought that the tree may not be able to assign the rows he is showing to one that was just queried from the database.

then i read this:

[Infralution]

Overriding the IsEqual and GetHashCode methods is only a good idea if the underlying objects really are identical (eg two strings may be different objects - but their contents are identical so IsEqual and GetHashCode can be safely overridden).

For objects like DataRows overriding IsEqual to return true if (for instance some primary key is equal) is likely to cause issues. This is because the two objects may well have different contents. Virtual Tree may hold one copy of the DataRow while your DataSet actually now has a different copy. So when you get the SelectedItems you may actually be getting an old DataRow.

Probably the best solution in this case if you want to keep the expansion state is to handle the RowExpand and RowCollapse events and track the currently expanded rows (by adding them to a collection). Then when you reload the DataSet you can iterate through the collection finding the new DataRows that correspond to the old DataRows and expand the correspong Virtual Tree row.
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Infralution Support