What are the most important parts of the .NET framework for a beginner?

Question

You often see, on sites like The Daily WTF, examples of overengineered code that should have just been a call to a built-in method within the .NET framework.

What namespaces/classes should be considered essential knowledge for a developer starting his/her first .NET job?

As per Joel Spolsky's instruction for these types of questions, please limit your answers to individual items for voting purposes.

Answer 1

System.String

and learn how to use regular expressions that are exposed via the System.Text.RegularExpressions namespace.

This will save you a huge amount of time if you end up re-writing text parsers or other string related tasks that have built in functions for them already.

http://www.regular-expressions.info/dotnet.html

And the daily WTF is awesome :D

Answer 2

http://msdn.microsoft.com/en-us/library/system.xml.aspx

System.Xml is also very good. Learn how to use these classes/methods so that you can manipulate XML files very quickly and easily without reinventing the wheel. Even if you never use XML yourself, you will come across it everywhere. Put some time into learning:

XML

XSLT

Schemes

RSS

SOAP

As all of these are used extensively in .net applications. You can find good information for almost all of these at:

http://www.w3schools.com/

And also; when you learn how to use it - please don't abuse it :D

Answer 3

using System;

System is probably the most important namespace as it contains the core features such as Object and Array as well as the GC (Garbage Collector).

Answer 4

System.Data, particularly Datatable,

Answer 5

System;
System.Collections;
System.Collections.Generic;

Answer 6

System.IO is very important.

Understanding how Streams and the various implementations work (FileStream, MemoryStream, CompressionStream) when combined with binary data or text from a TextReader/TextWriter instance is an essential skill.

Answer 7

You should thoroughly look over this application. It contains many patterns and best practices that you should follow.

patterns & practices Guidance Explorer

Answer 8

If you're working in VB.NET I'd say the My namespace is very important. It contains shortcuts to a lot of areas of the framework that used to be spread all over the place in the framework. It's also quite intuitive. You can write things like:
For Each Printer in My.Computer.Printers
or
My.Computer.FileSystem.OpenFile(Filename)
My.Computer.Info.AvailablePhysicalMemory
My.Computer.Screen.PrimaryScreen.WorkingArea

Answer 9

System.IDisposable

Not properly disposing objects that implement it (streams, database connections, sockets, etc) leads to locked file errors, open database connections and a whole lot of other unpleasant and hard to find bugs in your software.

http://www.codeproject.com/KB/cs/idispose.aspx

Answer 10

• System.IO for file operations
• System.Collections & System.Collections.Generic - learn how to manipulate / use Lists, Dictionary, etc.

Answer 11

There should be some line to be drawn between a Windows Developer and a Web Developer, where either can be using the .NET Framework. System.Web is very useful if you are doing Web Development as well as knowing how .NET interacts with IIS, while this may be irrelevant for a Developer who does Windows and Console Applications.

These are starting to blur at times so a developer should try to see where they want to be in the stack, e.g. do they want to do it all like in a small business environment or focus mainly on development like bigger shops can do.

Answer 12

System.Brains and System.CommonSense