Infralution Support

[jkempner]

I have a very large List that I'm using as the data source for a VirtualTree. I'm using VirtualTree 3.14.

The problem that I'm having is that it doesn't seem to create the row cache after I add a number of rows to the List and call UpdateRows. The result is that scrolling is painfully slow (many seconds to scroll down by a single page) until each row has been displayed once. Once all the rows have been displayed, and presumably the row cache has been build, scrolling is reasonably quick.

The long delay in adding to the row cache is because the backing data comes from a database hosted over the LAN, and accessing large numbers of records from that database can be slow.

Is there a way to force all the rows to be cached when the data are loaded so the scrolling performance will be usable? The VirtualTree control is in a dialog where the data are loaded when the dialog itself loads, with suitable feedback to the user about the load time progress, so if caching the data adds to the dialog load time, that's perfectly acceptable.

[Infralution]

Normally you would to make use of the virtual paging capability in this sort of scenario - otherwise your customer will have to wait much longer for all the data to load. However it you really want to force loading upfront you should be able to do this. Depending on your data source you can either do this yourself (ie fetch all the data into local memory before binding the data to Virtual Tree). Alternatively you could force Virtual Tree to enumerate all the rows by calling:

[jkempner]

The good news is that calling GetRows(), even on the main thread, doesn't add appreciably to the dialog's load time. The bad news is that it doesn't seem to help - scrolling through the tree the first time is still painfully slow. For whatever reason, GetRows() doesn't appear to build the row cache.

[Infralution]

What is the value of the LastRowIndex property when call GetRows. You need to call GetRows after the DataSource has been set so that this has been evaluated. Calling GetRows like this forces VirtualTree to create the Row objects and call IList[index] to get the item at each index of the bound data source. How this affects your application depends on how you have implemented the datasource. Have you build a custom datasource that implements IList to get virtual loading?
_________________
Infralution Support

[jkempner]

LastRowIndex is equal to the number of rows that should be loaded into the control at the time GetRows is called. I made sure of that before posting my follow-up question.

Unfortunately, the data source doesn't implement IList. It might be possible to tweak it so that it does - would this be expected to solve the problem?

[Infralution]

Virtual Tree requires the DataSource to implement the IList interface so I'm pretty sure it already does - but it just depends on how this is implemented. What is the data source you are binding to? How does the data get marshalled over the network?
_________________
Infralution Support

[jkempner]

I've simplified the programmatic data binding to be more efficient. There were two columns with CheckBox editors where OnGetCellData wasn't using the DataSource, and that's now fixed. So yes, DataSource implements IList - it's just a List<T>, where the data type is a custom type that's database-backed.

It seems that the best solution is to force the local cached copy of the backing database to be used instead of trying to marshal the data over the network. Doing this seems to solve the problem for all intents and purposes.