Edit Box – Line Numbers

One of the things making the development of detecting line changes involving selections difficult is not seeing which lines are being referred to by the line numbers being reported without continuously counting lines on the screen.  Therefore, lines numbers were added to the edit box.  How to do this was discovered in the Code Editor Example in the Qt documentation, which was linked to from the QPlainTextEdit help page.  It can also be found by search for "Code Editor" using the help page search.

This code was utilized in the edit box with several changes (only the code dealing with line numbers was used).  The example contains documentation, but this code essentially adds a widget on the left side of the edit box text area.  The background color of this widget is set to light gray and the line numbers are drawn into this widget.

The example code only made the width of the line number widget wide enough to hold the maximum line number plus three pixels on the left side of the numbers.  This made the line numbers look bunched in, so a full space was added to each side of the numbers.

The example code also started line numbers at one, but the line numbers in the document actually start at zero.  This needs to be taken account when calculating the widget of the line number widget and when drawing the line numbers to the widget.  However, for debugging purposes (the reason line numbers were added), it makes more sense to start the line numbers at zero.  Therefore, a BaseLineNumber definition was added to set the base line number.  For debugging, this will be set to a zero, but once this is no longer needed, this definition will be set to one.

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