c# Setting new registry value only if registry value name already exists

Question

My problem is that when I am using the Registry.SetValue I only want it to update an existing value. If a value name is entered that does not exist, I do not want to create it. I have variable data that the user enters, so I can not hardcode paths within my code.

My Code for my Set

    public class SetRegistryValue : CodeActivity
{
    [RequiredArgument]
    public InArgument<string> kpath { get; set; }

    public InArgument<string> txtName { get; set; }

    [RequiredArgument]
    public InArgument<string> kvaluename { get; set; }

    [RequiredArgument]
    public InArgument<string> kvalue { get; set; }

    //This will set the value of an key that is defined by user
    protected override void Execute(CodeActivityContext context)
    {

        string KeyPath = this.kpath.Get(context);
        string KeyValueName = this.kvaluename.Get(context);
        string KeyValue = this.kvalue.Get(context);
        string KeyName = Path.GetDirectoryName(KeyPath);
        string KeyFileName = Path.GetFileName(KeyPath);
        string fullKeyPath = KeyName + "\\" +  KeyFileName;

        Registry.SetValue(fullKeyPath, KeyValueName, KeyValue, RegistryValueKind.String);
    }
}

Answer 1

Use the Registry.GetValue() method:

Retrieves the value associated with the specified name, in the specified registry key. If the name is not found in the specified key, returns a default value that you provide, or null if the specified key does not exist.

If you want to test whether the keyName exists, test for null:

var myValue
  = Registry.GetValue(@"HKEY_CURRENT_USER\missing_key", "missing_value", "hi");

// myValue = null (because that's just what GetValue returns)

If you want to test whether the valueName exists, test for your default value:

var myValue
  = Registry.GetValue(@"HKEY_CURRENT_USER\valid_key", "missing_value", null);

// myValue = null (because that's what you specified as the defaultValue)

---

If the path could be invalid, you could try surrounding it with a try/catch block:

try
{
    var myValue = Registry.GetValue( ... );  // throws exception on invalid keyName

    if (myValue != null)
        Registry.SetValue( ... );
}
catch (ArgumentException ex)
{
    // do something like tell user that path is invalid
}