Friday, February 06, 2015

PySide Tree Tutorial IIID: Creating the tree with setupModelData()

Part of a series on treebuilding in PySide: see Table of Contents
Recall that TreeModel uses setupModelData() to set up the initial tree structure. We provide a very brief description of its behavior here, and refer the reader to the code itself for more details (the code is in post IIIA). We begin with a text file (default.txt) that contains all the data for our tree:
Getting Started            How to familiarize yourself with Qt Designer
Launching Designer         Running the Qt Designer application
The User Interface         How to interact with Qt Designer
Connection Editing Mode    Connecting widgets together
Connecting Objects         Making connections in Qt Designer
Editing Connections        Changing existing connections
The entire text file is extracted in main, and sent to setupModelData() within TreeModel. Two tab-delimited strings are extracted from each line (the title and summary), and form the basis for a new TreeItem. The location of each node in the hierarchy is determined by the pattern of indentation in the file. We construct the tree exactly as discussed in Part II, using the following rules:
  • For each line, create a TreeItem in which the two tab-delimited strings on that line are assigned to TreeItem.itemData (Figure 4, post IIB).
  • If line N+1 is indented relative to line N, then make the (N+1)th item a child of item N.
  • If line N+1 is unindented relative to line N, then make the (N+1)th item a sibling of item N's parent.
The implementation details in setupModelData() look a bit complicated, but most of the code is there for recordkeeping (e.g., keeping track of the current level of indentation). I found it helpful to work through how it handles the very first line of the input file, and then keep iterating through the code by hand until everything is clear.

No comments: