How to combine two NameValueCollections?

Question

I have two NameValueCollections:

NameValueCollection customTag = (NameValueCollection)System.Configuration.ConfigurationManager.GetSection("secureAppSettings");
NameValueCollection appSetting = (NameValueCollection)System.Configuration.ConfigurationManager.GetSection("appSettings");

I tried customTag.Add(appSetting); method but I get this error: Collection is read-only.

How would I combine them to one, so i can access all the elements from both?

Answer 1

To combine the collections, try something like the following:

var secureSettings = (NameValueCollection)System.Configuration.ConfigurationManager.GetSection("secureAppSettings");
var appSettings = (NameValueCollection)System.Configuration.ConfigurationManager.AppSettings;

// Initialise a new NameValueCollection with the contents of the secureAppSettings section
var allSettings = new NameValueCollection(secureSettings);
// Add the values from the appSettings section
foreach (string key in appSettings)
{
    // Overwrite any entry already there
    allSettings[key] = appSettings[key];
}

Use the new allSettings collection to access the combined settings.

Answer 2

I tried customTag.Add(appSetting); method but I get this error: Collection is read-only.

This means the customTag object is read only, and can't be written to. .Add attempts to modify the original NameValueCollection. System.Configuration contains a ReadOnlyNameValueCollection that extends NameValueCollection to make it read only, and so despite casting to the generic NameValueCollection, the object is still read only.

How would I combine them to one, so i can access all the elements from both?

All you need is to add both collections to a third writable NameValueCollection.

Given:

var customTag = (NameValueCollection)System.Configuration.ConfigurationManager.GetSection("secureAppSettings");
var appSetting = (NameValueCollection)System.Configuration.ConfigurationManager.GetSection("appSettings");

You could .Add both:

var collection = new NameValueCollection();
collection.Add(customTag);
collection.Add(appSettings);

However, the NameValueCollection constructor has a shorthand that calls Add internally:

var collection = new NameValueCollection(customTag);
collection.Add(appSettings);

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Be aware, that in both cases, using Add will allow multiple values to be added to each key.

For example, if you were to merge {foo: "bar"} and {foo: "baz"} the result would be {foo: ["bar", "baz"]} (JSON syntax used for brevity).