Adding Links for Tasks

Tasks linking is a fundamental operation when modeling project dependencies in Microsoft Project (MPP/XML) files. This article demonstrates how to programmatically add and visualize task dependencies using both VSTO and Aspose.Tasks for .NET.

Introduction

In project management, task links define how activities depend on one another. These dependencies — such as Finish-to-Start or Start-to-Start — ensure that tasks follow a logical execution sequence.

When working with Microsoft Project programmatically, you can establish these links using either:

• VSTO and COM interop: tightly coupled with the Microsoft Project desktop application.
• Aspose.Tasks for .NET: a platform-independent, server-safe API for manipulating project files.

Below are examples of both approaches for linking tasks.

Link Tasks Using VSTO

The following example demonstrates how to create a chain of Finish-to-Start dependencies using Microsoft.Office.Interop.MSProject.

⚠ Requires Microsoft Project to be installed and accessible on the machine.

Microsoft.Office.Interop.MSProject.Application projectApplication = new Application();
object missingValue = System.Reflection.Missing.Value;

projectApplication.FileOpenEx(@"D:\Aspose\Migration\SampleProject.mpp",
    missingValue, missingValue, missingValue, missingValue,
    missingValue, missingValue, missingValue, missingValue,
    missingValue, missingValue, PjPoolOpen.pjPoolReadOnly,
    missingValue, missingValue, missingValue, missingValue,
    missingValue);

Microsoft.Office.Interop.MSProject.Project project = projectApplication.ActiveProject;

// Add task dependencies using Finish-to-Start links
project.Tasks.get_UniqueID(2).TaskDependencies.Add(project.Tasks.get_UniqueID(1), PjTaskLinkType.pjFinishToStart);
project.Tasks.get_UniqueID(3).TaskDependencies.Add(project.Tasks.get_UniqueID(2), PjTaskLinkType.pjFinishToStart);
project.Tasks.get_UniqueID(4).TaskDependencies.Add(project.Tasks.get_UniqueID(3), PjTaskLinkType.pjFinishToStart);
project.Tasks.get_UniqueID(5).TaskDependencies.Add(project.Tasks.get_UniqueID(4), PjTaskLinkType.pjFinishToStart);
project.Tasks.get_UniqueID(5).TaskDependencies.Add(project.Tasks.get_UniqueID(2), PjTaskLinkType.pjFinishToStart);

// Print dependencies to console
foreach (Task tsk in project.Tasks)
{
    foreach (TaskDependency dep in project.Tasks.get_UniqueID(tsk.ID).TaskDependencies)
    {
        Console.WriteLine("From ID = " + dep.From.ID + " => To ID = " + dep.To.ID);
    }
    Console.WriteLine("____________________________________________________________");
}

// Save and close the project
projectApplication.FileCloseAll(Microsoft.Office.Interop.MSProject.PjSaveType.pjSave);

Key Notes:

• TaskDependencies.Add() links a predecessor and successor using a defined PjTaskLinkType.
• Interop requires verbose code and careful handling of COM objects.
• The get_UniqueID(taskID) method is used to access specific tasks for linking.

Link Tasks Using Aspose.Tasks for .NET

Aspose.Tasks offers a modern and streamlined way to define task dependencies programmatically without relying on Microsoft Project or COM components.

Project project = new Project("New Project.mpp");

Task task1 = project.RootTask.Children.GetById(1);
Task task2 = project.RootTask.Children.GetById(2);
Task task3 = project.RootTask.Children.GetById(3);
Task task4 = project.RootTask.Children.GetById(4);
Task task5 = project.RootTask.Children.GetById(5);

// Link the tasks
TaskLink taskLink = project.TaskLinks.Add(task1, task2, TaskLinkType.FinishToStart);
taskLink = project.TaskLinks.Add(task2, task3, TaskLinkType.FinishToStart);
taskLink = project.TaskLinks.Add(task3, task4, TaskLinkType.FinishToStart);
taskLink = project.TaskLinks.Add(task4, task5, TaskLinkType.FinishToStart);
taskLink = project.TaskLinks.Add(task2, task5, TaskLinkType.FinishToStart);

// Display links among the tasks
TaskLinkCollection allinks = project.TaskLinks;
foreach (TaskLink link in allinks)
{
    Console.WriteLine("From ID = " + link.PredTask.Get(Tsk.Id) + " => To ID = " + link.SuccTask.Get(Tsk.Id));
    Console.WriteLine("________________________________________");
}
 
project.Save("LinkTasks_out.mpp", SaveFileFormat.MPP);

Highlights:

• project.TaskLinks.Add(task1, task2, TaskLinkType.FinishToStart) adds a direct link between any two tasks.
• All task relationships are stored in the TaskLinkCollection.
• Each link exposes properties like PredTask, SuccTask, LinkType, and Lag.

The API is intuitive, concise, and ready for server-side use in ASP.NET, Azure Functions, or background services.

Comparison Table

Feature	VSTO / Interop	Aspose.Tasks for .NET
Requires MS Project	✅ Yes	❌ No
Supported Environments	🖥 Desktop only	☁ Desktop, Web, Cloud, Containers
Dependency Type	COM Interop	Pure .NET assembly
API Simplicity	⚠ Verbose and boilerplate-heavy	✅ Clean and object-oriented
Task Link Management	TaskDependencies collection	TaskLinks collection
Cross-platform support	❌ No	✅ Yes

Conclusion

Linking tasks is critical for maintaining project logic. While VSTO offers native access to Microsoft Project, its reliance on the desktop environment and COM interop makes it less suitable for modern applications.

Aspose.Tasks for .NET provides a clean and scalable alternative that simplifies task relationship management. Its flexibility and platform independence make it ideal for integrating into CI/CD pipelines, server apps, and web platforms.

To learn more about task relationships or scheduling logic, explore:

• Adding a New Task with Aspose.Tasks vs VSTO
• Create Resources and Link with Tasks
• Reading the Critical Path