C# Snippet Tutorial - Editing the Windows Registry

In this tutorial, I'm going to go through the code required to edit the Windows registry using C#. This will include creating new keys and values as well as modifying existing ones.

The registry is a great way to save information between application launches. Many applications use the registry to save information about dialog sizes and placements. That way the user doesn't have to resize and move dialogs every time the program starts.

Let's start by creating a new registry key. The first thing we need to decide is where to put our new key. If you bring up the Registry Editor - type "regedit" in the run bar, you'll notice the registry looks a lot like a file explorer. "Computer" is the root node with several child folders branching from it.

Most software packages will have a registry key inside

HKEY\_LOCAL\_MACHINE-\>SOFTWARE

These keys are available no matter who is logged in and is a good place to stick general application values. Let's put a key in this folder called "My Registry Key".

Registry.LocalMachine.CreateSubKey("SOFTWARE\\My Registry Key");

Registry is a class located in theMicrosoft.Win32 namespace. Registry.LocalMachine means where going to be modifying the HKEY_LOCAL_MACHINE registry key. We passed in "SOFTWARE\\My Registry Key" to CreateSubKey because we wanted our new key created inside the "SOFTWARE" key. CreateSubKey has the option to take more arguments - mostly dealing with access and security, but they're not important for this tutorial.

If you open the Registry Editor again, you'll now see you're new key. A key without any values is pretty useless, so let's add a string value to it.

RegistryKey myKey = Registry.LocalMachine.OpenSubKey("SOFTWARE\\My Registry Key", true);

myKey.SetValue("My String Value", "Test Value", RegistryValueKind.String);

The OpenSubKey method is called to get a reference to our newly created key. It takes the path to the key, which is the same as when creating it, and it takes a boolean indicating whether or not we want to open it writable. Since we want to add a new value to this key, we want to set this to true.

Next, we simply call SetValue to create our new value. The SetValue function takes the name of the value as the first argument, the actual value as the second, and the type of value as the third. The RegistryValueKind enumeration has lots of different kinds of data, so most primitive types can be stored in the registry. If the value you're trying to set doesn't exist yet (like in this case), SetValue will create it for you.

Now let's look at how to get values back out of the registry. It's very similar to setting values and equally as easy.

RegistryKey myKey = Registry.LocalMachine.OpenSubKey("SOFTWARE\\My Registry Key", false);

string myValue = (string)myKey.GetValue("My String Value");
//myValue now equals "Test Value"

We get a reference to our key exactly like we did before except this time we pass false for the writable argument. A call to GetValue is then made to retrieve the value from the registry. This function returns an object, so it must first be cast to your desired type - in this case string. It's always wise to check that the return value is not null before casting it since it is possible that the registry value you're trying to read doesn't exist.

That's all the code required to read and write to the Windows registry using .NET and C#.