How to: Plan tasks with dependencies

Keep the tasks in a Gantt chart in the right order: link tasks, either let dependent tasks follow a change or just report what's broken, and count durations in working time.

Requires WKL Forms Object Library 1.23 or later.

Dependencies come from a table (DependencySource with PredecessorField, SuccessorField, LinkTypeField, and LagField) or from a text field of the successor (PredecessorsField). ScheduleMode determines what a change does: wgsManual doesn't move anything and lists broken dependencies in Violations, while wgsAutomatic moves the dependent tasks. Working time comes from WorkDays, WorkHours, and the nonworking days in HolidaySource; DurationUnit counts in days or hours. Users link and unlink tasks with Ctrl+F2 and Ctrl+Shift+F2, from the shortcut menu, or by dragging from the end of one bar to another.

With Me!Gantt1.Object
    ' Dependencies as text in the task record instead of a table: "3FS+2;5SS"
    ' (FS finish-to-start, SS start-to-start, FF finish-to-finish, SF start-to-finish; lag in DurationUnit).
    .DependencySource = ""
    .PredecessorsField = "Predecessors"
 
    ' Calendar: Monday to Saturday, 7:00-12:00 and 12:30-16:00, nonworking days from a table.
    .WorkDays = 2 + 4 + 8 + 16 + 32 + 64            ' bit 1 = Sunday ... bit 64 = Saturday
    .WorkHours = "07:00-12:00;12:30-16:00"
    .HolidaySource = "tblHolidays": .HolidayField = "Day"
 
    ' Automatic scheduling: link 3 -> 4 with one working day lag; 4 and its successors follow.
    .ScheduleMode = wgsAutomatic
    .LinkTasks 3, 4, wglFinishToStart, 1
    .SetTaskDates 3, #10/8/2026#, #10/12/2026#     ' 4 moves again
 
    ' Manual: nothing moves; broken dependencies are listed and drawn red.
    .ScheduleMode = wgsManual
    Dim item As Variant
    For Each item In .Violations
        Debug.Print item
    Next
    .Reschedule                                     ' "Reschedule project": everything as early as allowed
 
    Debug.Print .TaskDuration(3), .TaskSlack(3), .IsCritical(3)
End With

• A finish is a task's last working day (with DurationUnit = hours, the moment work ends). A task that spans a nonworking day has one working day less; the finish stays where the data puts it.
• Automatic scheduling never moves tasks that have no dependencies or constraints, so the first Reschedule doesn't reshuffle a schedule that was typed in by hand.
• In automatic mode, a task moved by hand gets a “Start No Earlier Than” constraint; map ConstraintTypeField and ConstraintDateField to keep it across sessions.
• LinkTasks rejects a dependency that would create a cycle (wkeCycle) and one between a task and its own summary task (wkeInvalidValue); nothing is written in that case.
• The outline is part of the schedule: IndentTask and OutdentTask (Alt+Shift+Right/Left, or Indent/Outdent on the shortcut menu) make a task a subtask of the task above it or move it out of its summary task; TaskResources and Assign resources … assign resources.
• Changes made in code don't raise events. The same changes made by the user raise BeforeTaskChange, BeforeLinkAdd, or BeforeLinkDelete, where VBA can adjust or cancel them.

• API reference: LinkTasks, ScheduleMode, Violations
• Tutorial: Create a project plan
• WklGantt overview