ProjectScheduler

What it is for

This is the engine behind the GanttChart, the PertChart and the TaskBoard: each chart schedules its plan through it and draws the result, so the three always agree. Call it yourself to work with the same dates without a chart – a report, an export, a check on the server before a plan is saved.

How a plan is scheduled

1. The outline is read: each task finds its parent, and every task gets an outline number (ScheduledTask.Wbs).
2. Each task's own dates are read: its duration in working days, its planned start and any ProjectTask.Constraint.
3. The links are checked, and any that cannot be honoured are reported and left out.
4. The forward pass gives every task its earliest dates: as soon as its links, its summary, its planned start and the project's start allow.
5. The backward pass gives every task its latest dates: as late as it can be without moving the project's finish.
6. Float, the critical path and summaries' progress are worked out from the two.

Bad data is never fatal

A duplicate id, a link to a task that is not there, a loop of links: each is reported in ProjectSchedule.Problems and left out, and everything else is still scheduled. The scheduler does not throw for anything in the plan.

Working days

Durations and lags count working days on the calendar of ScheduleInput.WorkingDays and ScheduleInput.Holidays, so a five-day task that starts on a Thursday finishes on the following Wednesday. Dates have no time of day and no time zone, so a plan schedules to the same dates on every machine.

A website plan of eight tasks, scheduled on a Monday-to-Friday week from Monday 2 November 2026. The comments give the dates the scheduler works out.

using System;
using System.Collections.Generic;

List<ProjectTask> tasks = new List<ProjectTask>
{
    new ProjectTask("design", "Design"),                                   // summary
    new ProjectTask("brief", "Agree the brief", 3) { ParentId = "design" },
    new ProjectTask("wire", "Wireframes", 5) { ParentId = "design" },
    new ProjectTask("build", "Build"),                                     // summary
    new ProjectTask("front", "Front end", 10) { ParentId = "build" },
    new ProjectTask("api", "Order API", 8) { ParentId = "build" },
    new ProjectTask("test", "User testing", 4),
    new ProjectTask("live", "Go live", 0)                                  // milestone
};

List<TaskLink> links = new List<TaskLink>
{
    new TaskLink("brief", "wire"),
    new TaskLink("wire", "front"),
    new TaskLink("wire", "api", TaskLinkType.StartToStart, 2),
    new TaskLink("build", "test"),                                         // after all of Build
    new TaskLink("test", "live")
};

ProjectSchedule schedule = ProjectScheduler.Schedule(tasks, links, new DateTime(2026, 11, 2));

// brief  Mon 2 Nov  - Wed 4 Nov
// wire   Thu 5 Nov  - Wed 11 Nov
// api    Mon 9 Nov  - Wed 18 Nov   (5 working days of float)
// front  Thu 12 Nov - Wed 25 Nov
// test   Thu 26 Nov - Tue 1 Dec
// live   Tue 1 Dec
Console.WriteLine(schedule.ProjectFinish.ToString("yyyy-MM-dd"));      // 2026-12-01
Console.WriteLine(string.Join(" > ", schedule.CriticalPath));         // brief > wire > front > test > live
Console.WriteLine(schedule.Find("api").TotalFloat);                   // 5

foreach (ScheduleProblem problem in schedule.Problems)
{
    Console.WriteLine(problem.Message);                                // none for this plan
}