Although the window object for the visual presentation of tree-like data structures (tree view) is somewhat apart from other list views, I nevertheless decided to place it in the place that it usually occupies on the component bar - after the general list view.

I note right away that the performance of the system tree view when working with a large number of elements leaves much to be desired. In addition, there is a system limit on the maximum number of nodes in a tree (65536). As more nodes are added, the window cannot even show the scroll bars, and tree viewing becomes problematic.

 

There are a number of recommendations (in terms of speed optimization) for programmers who use this visual element in their interfaces. Namely:

 

•avoid loading the whole tree. Nodes should be loaded as needed, when plowing up their parents;

•when constructing tree-organized data, one should prevent each individual node from containing too many slave nodes. Unfortunately, this very recommendation is rarely enforceable: the data is usually organized not by the programmer, but by the user. Example: file structure on disk.

•do not use this object for viewing trees, if you need a really high speed of work (or the total number of nodes cannot be limited to 65536). It is quite possible to display data in the form of a tree using the same general list from the previous chapter. This work can be done especially efficiently if you use a shared list in virtual list mode. At the same time, node data can be stored in memory using a simple TTree object (described above, in the section on simple, non-visual objects).

 

Nevertheless, a specially designed object for visual work with trees works well if the first two of these requirements are met, or in the case of small trees. Constructor:

 

NewTreeView(Parent, Options, IL_Normal, IL_State);

 

The following set of flags can be specified in the options:

 

tvoNoLines - do not show lines connecting nodes in the tree;

tvoLinesRoot - do not show lines for top-level nodes;

tvoNoButtons - do not show the buttons ("+" and "-") used to expand and collapse nodes;

tvoEditLabels - allows you to edit the text of nodes "in place" (F2 key or one more left-click when the mouse cursor is positioned on the text of the node;

tvoHideSel - hide the selection of the current node when the tree is not in the focus of keyboard input;

tvoDragDrop - automatically start the operation of "dragging" nodes with the mouse (by pressing the mouse button on the node and moving the cursor while the mouse is held down);

tvoNoTooltips - automatic display of the full text of nodes in a pop-up window when hovering over them with the mouse, if the text of the node does not completely fit into the client part of the window;

tvoCheckBoxes - system switches are automatically used as status icons for nodes;

tvoTrackSelect - visual tracking of mouse movement over nodes in the tree;

tvoSingleExpand - to expand only one node in the tree (all other nodes automatically collapse when another node is expanded, unless you clicked the mouse while pressing the Control key;

tvoInfoTip - sends a request to the object to get the text to show in the pop-up window for each node in the tree;

tvoFullRowSelect - full line selection;

tvoNoScroll - lack of scrolling in the window;

tvoNonEvenHeight - odd height for elements (by default, the line height must be an even number).

 

The main way to identify nodes in a tree is not their index, but node descriptors, i.e. integers that are one-to-one assignments to elements when they are added. Unlike the TTreeView component in the VCL, the tree view object in KOL does not create an in-memory object for each node in the tree, similar to the VCL's TTreeNode.

 

The general properties of the list window objects also work for the tree:

 

Count - returns the number of nodes in the tree (however, if the number of nodes exceeds 65536, the system always returns 0, and cannot show the scroll bar);

ImageListNormal - a list of images for storing thumbnails of the main images for elements;

ImageListState - a list of images for storing state icons;

OnSelChange - an event that is triggered when another node becomes selected in the tree;

 

Properties, events, and methods that can be considered specific to the treeview object begin with the TV prefix.