TaskLink

What it is for

Links are what turn a list of tasks into a schedule: the charts put each task as early as its links, its planned start and the project's start allow, and the chain of links with no room to spare is the critical path. Keep them in a collection beside the tasks and give it to each chart's Links property. A link the reader draws on the Gantt chart, or types into its Predecessors cell, is added to that collection; one the reader deletes is removed from it.

Links and summaries

A link into a summary task holds back every subtask in it, and a link out of one waits for all of them. Because a summary's dates belong to its subtasks, only TaskLinkType.FinishToStart and TaskLinkType.StartToStart can lead into a summary, and only TaskLinkType.FinishToStart and TaskLinkType.FinishToFinish can lead out of one.

Links that cannot be used

Nothing about a link ever stops a chart drawing. A link that names a missing task, joins a task to itself, repeats another link of the same type between the same tasks, joins a summary to one of its own subtasks, uses a type a summary cannot honour, or closes a loop of tasks waiting for each other is left out of the schedule and reported in ProjectSchedule.Problems.

using System.Collections.ObjectModel;

ObservableCollection<TaskLink> links = new ObservableCollection<TaskLink>
{
    new TaskLink("brief", "wire"),                                // wireframes after the brief
    new TaskLink("wire", "front"),                                // front end after the wireframes
    new TaskLink("wire", "api", TaskLinkType.StartToStart, 2),    // the API two working days into the wireframes
    new TaskLink("build", "test"),                                // testing after the whole Build phase
    new TaskLink("test", "live")                                  // go live once testing is done
};