Resx

Resx is the XML-based resource file format used by the .NET framework to store resources such as strings, images, icons, and other data used by an application. Files use the .resx extension and are intended to be portable between platforms supported by .NET, with tooling in Visual Studio and the .NET SDK to read, write, and compile them.

A resx file contains a root element, followed by metadata in resheader elements and multiple data entries. Each data entry has a name attribute and a value element, and may include optional type and mimetype attributes. The value can be a plain string or a value that represents more complex resources such as images or serialized objects. Resx supports binary data by encoding it in the value element and associating a type, such as System.Drawing.Bitmap, to indicate how to interpret it. The resheader elements carry metadata like version, generator, and language.

Localization and usage in applications are typically handled by culture-specific resx files. A default resource file (e.g., Strings.resx) provides fallback values, while culture-specific files (e.g., Strings.en-US.resx, Strings.fr.resx) supply translations. At runtime, ResourceManager loads the appropriate resource set for the current culture, and resources can be embedded into assemblies as satellite assemblies for localization.

Build tools and access patterns: a resx file is processed by resgen to produce a .resources binary file, which is then embedded in the assembly or loaded at runtime. Visual Studio can generate a strongly-typed resource class from a resx file using a code generator like ResXFileCodeGenerator, enabling access via Properties.Resources. Developers can also read and write resx files programmatically using ResXResourceReader and ResXResourceWriter.

Best practices include keeping keys stable, adding comments for translators, organizing resources by feature, and avoiding large binary data in resx when possible.