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Sheets

Every displayed screen is an instance of Sheet, which manages its rows, columns, cursor, and display.

These will each be described in detail below. See the API reference for the full API.

Sheet Example Code

Here is the complete code for a simple DictSheet.

# rowdef: source key
class DictSheet(Sheet):
    rowtype = 'items'
    columns = [
        Column('key'),
        Column('value', getter=lambda col,row: col.sheet.source[row])
    ]
    def reload(self):
        self.rows = list(self.source.keys())

globalCommand('1', 'vd.push(DictSheet("globals", source=globals()))', 'push globals dict')

If this code is loaded, pressing 1 will push a fresh instance of DictSheet, showing each key in the globals() dict with its corresponding value.

The Essential Steps to Create a Sheet

1. Gather the name and sources for the constructor

Sheet(name, **kwargs)

The constructor of a sheet should always take a name (str). Additional Sheet parameters are passed via kwargs, and will be made available as attributes on the Sheet instance.

The source of a Sheet is usually passed into the constructor. For a sheet loaded from a file, the source will be a Path object.

Derived sheets will have other Sheet instances as their source.

But really, the source needed is dependent on that Sheet's reload() which collects the data.

2. Collect rows in Sheet.reload()

The reload() member on a Sheet must populate the

3. Enumerate the columns

Columns can either be specified in the class scope (as per the example), populated in the constructor (if dependent on the sources), or if necessary, populated by reload if dependent on the data itself.

4. Instantiate the sheet in a globalCommand

5. Enjoy your new sheet!

viewport

Here is a diagram of the screen layout:

[img]

row layout

  • topRowIndex index of row just below header row
  • nScreenRows: simply based on terminal height, the number of rows that can be displayed.
  • visibleRows: the contiguous slice of rows which is visible onscreen

Column layout is more involved:

  1. the first nKeys columns are 'key' columns, which are pinned to the left and always visible.
  2. columns are variable width.
  3. if a column's width is 0, it is not visible (hidden).

Invisible columns make it more difficult to move the column cursor sensibly. So Sheet has a computed property visibleCols, which is the better choice for most tasks. hidden columns still exist (go to the Columns sheet to unhide them), but they should remain invisible in most cases.

  • visibleCols: (O(ncols), cached between frames): list of all non-hidden columns
  • leftVisibleColIndex is the first non-key column on the left.
  • rightVisibleColIndex (computed by Sheet.calcColLayout(), assignment will be ignored)

the Row and Column Cursor [name=cursor]

The primary (settable) row cursor is cursorRowIndex, which is an index into rows.

The primary (settable) column cursor is cursorVisibleColIndex, which is an index into visibleCols.

The other cursor properties are computed:

  • cursorColIndex (O(ncols)); index into .columns
  • cursorRow: equivalent to rows[cursorRowIndex]
  • cursorCol: equivalent to columns[cursorColIndex] (and visibleCols[cursorVisibleColIndex])

the value at the cursor (the current cell)

  • cursorCell:
  • `

DisplayWrapper [name=display]

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