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POVirtualStringTree Correct/recommended use
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copied!<p>I have been using virtualstringtree for a while now. I use it for two different things, first a s a normal tree for selecting ,displaying data and secondly as a grid to show outputs from SQL statements.</p> <p>All my data loaded in to the trees is from a database. For the tree example, i have a parentId field to distinguish the heirarchy, and for the grid examples i simply use an SQL statement with a customized record for each tree (that is unique).</p> <p>My questions relates to the preferred/best way to populate the tree. I have read from the VST docs that you should use the onInitNode event along with rootnodecount. However i have found that using the AddChild() method to be very similar, even though it is not encouraged.</p> <p>Let me show some (simplified) examples:</p> <p><strong>1. Heirarchy</strong></p> <pre><code>type PData = ^rData; rData = packed record ID : Integer; ParentID : Integer; Text : WideString; end; procedure Loadtree; var Node : PVirtualNode; Data : PData; begin Q1 := TQuery.Create(Self); try Q1.SQL.Add('SELECT * FROM Table'); Q1.Open; Q1.Filter := 'ParentID = -1'; //to get the root nodes Q1.Filtered := True; while not Q1.Eof do begin Node := VST.AddChild(nil); Data := VST.GetNodeData(Node); Data.ID := Q1.Fields[fldID].AsInteger; Data.ParentID := Q1.Fields[fldParentID].AsInteger; Data.Text := Q1.Fields[fldText].AsString; //now filter the query again to get the children of this node PopulateChildren(Data.ParentID,Node); //add children to this node and do it recursively Q1.Next; end; finally Q1.free; end; end; </code></pre> <p><strong>2. Grid</strong></p> <pre><code>procedure LoadGrid; var Node : PVirtualNode; Data : PData; begin Q1 := TQuery.Create(self); try Q1.SQL.Add('SELECT * FROM Table'); Q1.Open; while not Q1.eof do begin Node := VST.AddChild(nil); Data.ID := Q1.Fields[fldID].AsInteger; Data.Text := Q1.Fields[fldText].AsString; Q1.Next; end; finally Q1.Free; end; end; </code></pre> <p>So essentially i am bypassing the RootNodeCount and OnInitNode methods/property and using the old fashioned way to add nodes to the tree. It seems to work fine. Note in the example i create and destroy my queries at runtime.</p> <p>The reason i started using the tree in this manner is that i could load all the data in the tree once and then free the TQuery after i had finished using it. I was thinking that regardless of keeping the TQuery alive/created i would still need to use my rData record to store the data, hence using up more memory if i did not destroy the TQuery. Currently my application uses about 250+MB when fully loaded, and can increase when i run SQL reports and display them in the VST. I have seen it use about 1GB of ram when i have run a SQL report with 20000+ nodes and 50+ columns. What i would like to know if the way i am using the VST incorrect with regards to minimizing memory usage?</p> <p>Would i be better off creating a query for the lifetime of the tree and using the onInitNode event? So that when data is requested by the tree it fetches it from the TQuery using the onInitNode/OnInitChildren event (i.e. the pure virtual paradigm of the tree)? Thus i would need to keep the TQuery alive for the duration of the form. Would there be any memory benefit/performance benefit in using it this way?</p> <p>In the above situations the i can see the difference for the grid example would be far less (if any) than the heirarchy - due to the fact that all nodes need to be initialized when populated.</p>

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