ResourceManager Class

When you develop a resource-based app, you store resource information in text files (files that have a .txt or .restext extension) or XML files (files that have a .resx extension). You then compile the text or XML files with the Resource File Generator (Resgen.exe) to create a binary .resources file. You can then embed the resulting .resources file in an executable or library by using a compiler option such as /resources for the C# and Visual Basic compilers, or you can embed it in a satellite assembly by using the Assembly Linker (Al.exe). If you include a .resx file in your Visual Studio project, Visual Studio handles the compilation and embedding of default and localized resources automatically as part of the build process.

Ideally, you should create resources for every language your app supports, or at least for a meaningful subset of each language. The binary .resources file names follow the naming convention basename.cultureName.resources, where basename is the name of the app or the name of a class, depending on the level of detail you want. The CultureInfo::Name property is used to determine cultureName. A resource for the app's default culture should be named basename.resources.

For example, suppose that an assembly has several resources in a resource file that has the base name MyResources. These resource files should have names such as MyResources.ja-JP.resources for the Japan (Japanese) culture, MyResources.de.resources for the German culture, MyResources.zh-CHS.resources for the simplified Chinese culture, and MyResources.fr-BE.resources for the French (Belgium) culture. The default resource file should be named MyResources.resources. The culture-specific resource files are commonly packaged in satellite assemblies for each culture. The default resource file should be embedded in the app's main assembly.

Note that Assembly Linker (Al.exe) allows resources to be marked as private, but you should always mark them as public so they can be accessed by other assemblies. (Because a satellite assembly contains no code, resources that are marked as private are unavailable to your app through any mechanism.)

For more information about creating, packaging, and deploying resources, see the articles Creating Resource Files, Creating Satellite Assemblies, and Packaging and Deploying Resources.

You instantiate a ResourceManager object that retrieves resources from an embedded .resources file by calling one of its class constructor overloads. This tightly couples a ResourceManager object with a particular .resources file and with any associated localized .resources files in satellite assemblies.

The two most commonly called constructors are:

• ResourceManager(String, Assembly) looks up resources based on two pieces of information that you supply: the base name of the .resources file and the assembly in which the default .resources file resides. The base name includes the namespace and root name of the .resources file, without its culture or extension. Note that .resources files that are compiled from the command line typically do not include a namespace name, whereas .resources files that are created in the Visual Studio environment do. For example, if a resource file is named MyCompany.StringResources.resources and the ResourceManager constructor is called from a static method named Example.Main, the following code instantiates a ResourceManager object that can retrieve resources from the .resources file:

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• ResourceManager(Type) looks up resources in satellite assemblies based on information from a type object. The type's fully qualified name corresponds to the base name of the .resources file without its file name extension. In desktop apps that are created by using the Visual Studio Resource Designer, Visual Studio creates a wrapper class whose fully qualified name is the same as the root name of the .resources file. For example, if a resource file is named MyCompany.StringResources.resources and there is a wrapper class named MyCompany.StringResources, the following code instantiates a ResourceManager object that can retrieve resources from the .resources file:

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If the appropriate resources cannot be found, the constructor call creates a valid ResourceManager object. However, the attempt to retrieve a resource throws a MissingManifestResourceException exception. For information about dealing with the exception, see the Handling MissingManifestResourceException and MissingSatelliteAssembly Exceptions section later in this article.

The following example shows how to instantiate a ResourceManager object. It contains the source code for an executable named ShowTime.exe. It also includes the following text file named Strings.txt that contains a single string resource, TimeHeader:

TimeHeader=The current time is

You can use a batch file to generate the resource file and embed it into the executable. Here's the batch file to generate an executable by using the C# compiler:

resgen strings.txt
csc ShowTime.cs /resource:strings.resources

For the Visual Basic compiler, you can use the following batch file:

resgen strings.txt
vbc ShowTime.vb /resource:strings.resources

A localized app requires resources to be deployed as discussed in the article Packaging and Deploying Resources. If the assemblies are properly configured, the resource manager determines which resources to retrieve based on the current thread's Thread::CurrentUICulture property. (That property also returns the current thread's UI culture.) For example, if an app is compiled with default English language resources in the main assembly and with French and Russian language resources in two satellite assemblies, and the Thread::CurrentUICulture property is set to fr-FR, the resource manager retrieves the French resources.

You can set the CurrentUICulture property explicitly or implicitly. The way you set it determines how the ResourceManager object retrieves resources based on culture:

• If you explicitly set the Thread::CurrentUICulture property to a specific culture, the resource manager always retrieves the resources for that culture, regardless of the user's browser or operating system language. Consider an app that is compiled with default English language resources and three satellite assemblies that contain resources for English (United States), French (France), and Russian (Russia). If the CurrentUICulture property is set to fr-FR, the ResourceManager object always retrieves the French (France) resources, even if the user's operating system language is not French. Make sure that this is the desired behavior before you set the property explicitly.

  In ASP.NET apps, you must set the Thread::CurrentUICulture property explicitly, because it is unlikely that the setting on the server will match incoming client requests. An ASP.NET app can set the Thread::CurrentUICulture property explicitly to the user's browser accept language.

  Explicitly setting the Thread::CurrentUICulture property defines the current UI culture for that thread. It does not affect the current UI culture of any other threads in an app.

• You can set the UI culture of all threads in an app domain by assigning a CultureInfo object that represents that culture to the static CultureInfoDefaultThreadCurrentUICulture() property.

• If you do not explicitly set the current UI culture and you do not define a default culture for the current app domain, the CultureInfo::CurrentUICulture property is set implicitly by the Windows GetUserDefaultUILanguage function. This function is provided by the Multilingual User Interface (MUI), which enables the user to set the default language. If the UI language is not set by the user, it defaults to the system-installed language, which is the language of operating system resources.

The following simple "Hello world" example sets the current UI culture explicitly. It contains resources for three cultures: English (United States) or en-US, French (France) or fr-FR, and Russian (Russia) or ru-RU. The en-US resources are contained in a text file named Greetings.txt:

HelloString=Hello world!

The fr-FR resources are contained in a text file named Greetings.fr-FR.txt:

HelloString=Salut tout le monde!

The ru-RU resources are contained in a text file named Greetings.ru-RU.txt:

HelloString=Всем привет!

Here's the source code for the example (Example.vb for the Visual Basic version or Example.cs for the C# version):

To compile this example, create a batch (.bat) file that contains the following commands and run it from the command prompt. If you're using C#, specify csc instead of vbc and Example.cs instead of Example.vb.

resgen Greetings.txt 
vbc Example.vb /resource:Greetings.resources

resgen Greetings.fr-FR.txt
Md fr-FR
al /embed:Greetings.fr-FR.resources /culture:fr-FR /out:fr-FR\Example.resources.dll

resgen Greetings.ru-RU.txt
Md ru-RU
al /embed:Greetings.ru-RU.resources /culture:ru-RU /out:ru-RU\Example.resources.dll

You call the GetObject(String) and GetString(String) methods to access a specific resource. You can also call the GetStream method to retrieve non-string resources as a byte array. By default, in an app that has localized resources, these methods return the resource for the culture determined by the current UI culture of the thread that made the call. See the previous section, ResourceManager and Culture-Specific Resources, for more information about how the current UI culture of a thread is defined. If the resource manager cannot find the resource for the current thread's UI culture, it uses a fallback process to retrieve the specified resource. If the resource manager cannot find any localized resources, it uses the resources of the default culture. For more information about resource fallback rules, see the "Resource Fallback Process" section of the article Packaging and Deploying Resources.

Note

If the .resources file specified in the ResourceManager class constructor cannot be found, the attempt to retrieve a resource by calling a specific resource retrieval method throws a MissingManifestResourceException exception. For information about dealing with the exception, see the Handling MissingManifestResourceException and MissingSatelliteAssemblyException Exceptions section later in this topic.

The following example uses the GetString method to retrieve culture-specific resources. It consists of resources compiled from .txt files for the English (en), French (France) (fr-FR), and Russian (Russia) (ru-RU) cultures. The example changes the current culture and current UI culture to English (United States), French (France), Russian (Russia), and Swedish (Sweden). It then calls the GetString method to retrieve the localized string, which it displays along with the current day and month. Notice that the output displays the appropriate localized string except when the current UI culture is Swedish (Sweden). Because Swedish language resources are unavailable, the app instead uses the resources of the default culture, which is English.

The example requires the text-based resource files listed in following table. Each has a single string resource named DateStart.

Here's the source code for the example (ShowDate.vb for the Visual Basic version or ShowDate.cs for the C# version of the code).

To compile this example, create a batch file that contains the following commands and run it from the command prompt. If you're using C#, specify csc instead of vbc and showdate.cs instead of showdate.vb.

resgen DateStrings.txt
vbc showdate.vb /resource:DateStrings.resources

md fr-FR
resgen DateStrings.fr-FR.txt
al /out:fr-FR\Showdate.resources.dll /culture:fr-FR /embed:DateStrings.fr-FR.resources 

md ru-RU
resgen DateStrings.ru-RU.txt
al /out:ru-RU\Showdate.resources.dll /culture:ru-RU /embed:DateStrings.ru-RU.resources

There are two ways to retrieve the resources of a specific culture other than the current UI culture:

• You can call the GetString(String, CultureInfo), GetObject(String, CultureInfo), or GetStream(String, CultureInfo) method to retrieve a resource for a specific culture. If a localized resource cannot be found, the resource manager uses the resource fallback process to locate an appropriate resource.

• You can call the GetResourceSet method to obtain a ResourceSet object that represents the resources for a particular culture. In the method call, you can determine whether the resource manager probes for parent cultures if it is unable to find localized resources, or whether it simply falls back to the resources of the default culture. You can then use the ResourceSet methods to access the resources (localized for that culture) by name, or to enumerate the resources in the set.

If you try to retrieve a specific resource, but the resource manager cannot find that resource and either no default culture has been defined or the resources of the default culture cannot be located, the resource manager throws a MissingManifestResourceException exception if it expects to find the resources in the main assembly or a MissingSatelliteAssemblyException if it expects to find the resources in a satellite assembly. Note that the exception is thrown when you call a resource retrieval method such as GetString or GetObject, and not when you instantiate a ResourceManager object.

The exception is typically thrown under the following conditions:

• The appropriate resource file or satellite assembly does not exist. If the resource manager expects the app's default resources to be embedded in the main app assembly, they are absent. If the NeutralResourcesLanguageAttribute attribute indicates that the app's default resources reside in a satellite assembly, that assembly cannot be found. When you compile your app, make sure that resources are embedded in the main assembly or that the necessary satellite assembly is generated and is named appropriately. Its name should take the form appName.resources.dll, and it should be located in a directory named after the culture whose resources it contains.

• Your app doesn't have a default or neutral culture defined. Add the NeutralResourcesLanguageAttribute attribute to a source code file or to the project information file (AssemblyInfo.vb for a Visual Basic app or AssemblyInfo.cs for a C# app) file.

• The baseName parameter in the ResourceManager constructor does not specify the name of a .resources file. The name should include the resource file's fully qualified namespace but not its file name extension. Typically, resource files that are created in Visual Studio include namespace names, but resource files that are created and compiled at the command prompt do not. You can determine the names of embedded .resources files by compiling and running the following utility. This is a console app that accepts the name of a main assembly or satellite assembly as a command-line parameter. It displays the strings that should be provided as the baseName parameter so that the resource manager can correctly identify the resource.

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If you are changing the current culture of your application explicitly, you should also remember that the resource manager retrieves a resource set based on the value of the CultureInfo::CurrentUICulture property, and not the CultureInfo::CurrentCulture property. Typically, if you change one value, you should also change the other.

Because the main assembly that contains an app's default resources is separate from the app's satellite assemblies, you can release a new version of your main assembly without redeploying the satellite assemblies. You use the SatelliteContractVersionAttribute attribute to use existing satellite assemblies and instruct the resource manager not to redeploy them with a new version of your main assembly,

For more information about versioning support for satellite assemblies, see the article Retrieving Resources in Satellite Assemblies.

For executables deployed and run from a Web site (HREF .exe files), the ResourceManager class may probe for satellite assemblies over the Web, which can hurt your application's performance. You can limit this probing to the satellite assemblies that you have deployed with your application, which eliminates the performance problem. To do this, you create a <satelliteassemblies> node in the application configuration file to specify that you have deployed a specific set of cultures for your application, and that the ResourceManager class should not attempt to probe for any culture that is not listed in that node.

Note
The preferred alternative to creating a <satelliteassemblies> node is to use the ClickOnce Deployment Manifest feature.

Create a configuration file section similar to the following code example:

<?xml version ="1.0"?>
<configuration>
    <satelliteassemblies>
        <assembly name="MainAssemblyName, Version=versionNumber, Culture=neutral, PublicKeyToken=null|yourPublicKeyToken">
            <culture>cultureName1</culture>
            <culture>cultureName2</culture>
            <culture>cultureName3</culture>
        </assembly>
    </satelliteassemblies>
</configuration>

In your configuration file, do the following:

• Specify one or more <assembly> nodes for each main assembly that you deploy, where the <assembly> node attribute specifies a fully qualified assembly name. Specify the name of your main assembly in place of MainAssemblyName, and specify the Version, PublicKeyToken, and Culture attribute values that correspond to your main assembly.

  For the Version attribute, specify the version number of your assembly. For example, the first release of your assembly might be version number 1.0.0.0.

  For the PublicKeyToken attribute, specify the keyword "null" if you have not signed your assembly with a strong name, or specify your public key token if you have signed your assembly.

  For the Culture attribute, specify the keyword "neutral" to designate the main assembly and cause the ResourceManager class to probe only for the cultures listed in the <culture> nodes.

  For more information about fully qualified assembly names, see Assembly Names. For more information about strong-named assemblies, see Creating and Using Strong-Named Assemblies.

• Specify one or more <culture> nodes with a specific culture name, such as "fr-FR", or a neutral culture name, such as "fr".

If resources are needed for any assembly not listed under the <satelliteassemblies> node, the ResourceManager class probes for cultures using standard probing rules.