Defining the program array for tree-views

The program array containing the tree-view nodes must use a specific record structure.

In the program code, define a dynamic array of records with the DEFINE instruction. The DISPLAY ARRAY dialog will use that program array as the model for the tree-view list. A tree of nodes will be automatically built based on the data found in the program array. The front-end can then render the tree of nodes in a tree-view widget.

The members of the program array must correspond to the elements of the screen-array bound to the TREE container, by number and data types.

The name of the array members does not matter; the purpose of each member is defined by the name of the corresponding screen-array members declared in the form file. Program array members and screen-array members are bound by position.

The next code example defines a program array with a member structure corresponding to the screen-array defined in the form example of the previous section.

DEFINE tree_arr DYNAMIC ARRAY OF RECORD
       name STRING,       -- text to be displayed for the node 
       pid STRING,        -- id of the parent node 
       id STRING,         -- id of the current node 
       image STRING,      -- name of the image file for the node (can be null)
       expanded BOOLEAN,  -- node expansion flag (TRUE/FALSE) (optional)
       isnode BOOLEAN,    -- children indicator flag (TRUE/FALSE) (optional)
       description STRING -- user field describing the node 
END RECORD

The name, pid, id members are mandatory. These hold respectively the node text, parent and current node identifiers that define the structure of the tree.

The image member will hold the name of the little icon to be displayed for each node and leaf. You can omit this member, if you do not want to display images, or when then tree defines default images with the IMAGEEXPANDED, IMAGECOLLAPSED and the IMAGELEAF attributes.

The expanded member can be used to handle node expansion by program. You can query this member to check whether a node is expanded, or set the value to expand a specific node.

The isnode member can be used to indicate whether a given node has children, without filling the array with rows defining the child nodes. This information will be used by front-ends to decorate a node as a parent, even if no children are present. it is recommended that the program then fill the array with child nodes when an expand action is invoked, to implement dynamic tree-views).

The program array can hold more columns (like the description field), which can be displayed in regular table columns as part of a node's data.

Remember the order of the program array members must match the screen-array members in the form file, but this order can be different from the column order used in the layout, with the exception of the first column defining the text of nodes (i.e. name field in example).