System.Resources.ResourceReader class

This article provides supplementary remarks to the reference documentation for this API.

The ResourceReader class provides a standard implementation of the IResourceReader interface. A ResourceReader instance represents either a standalone .resources file or a .resources file that is embedded in an assembly. It is used to enumerate the resources in a .resources file and retrieve its name/value pairs. It differs from the ResourceManager class, which is used to retrieve specified named resources from a .resources file that is embedded in an assembly. The ResourceManager class is used to retrieve resources whose names are known in advance, whereas the ResourceReader class is useful for retrieving resources whose number or precise names are not known at compile time. For example, an application may use a resources file to store configuration information that is organized into sections and items in a section, where the number of sections or items in a section is not known in advance. Resources can then be named generically (such as Section1, Section1Item1, Section1Item2, and so on) and retrieved by using a ResourceReader object.

Instantiate a ResourceReader object

A .resources file is a binary file that has been compiled from either a text file or an XML .resx file by Resgen.exe (Resource File Generator). A ResourceReader object can represent either a standalone .resources file or a .resources file that has been embedded in an assembly.

To instantiate a ResourceReader object that reads from a standalone .resources file, use the ResourceReader class constructor with either an input stream or a string that contains the .resources file name. The following example illustrates both approaches. The first instantiates a ResourceReader object that represents a .resources file named Resources1.resources by using its file name. The second instantiates a ResourceReader object that represents a .resources file named Resources2.resources by using a stream created from the file.

// Instantiate a standalone .resources file from its filename.
var rr1 = new System.Resources.ResourceReader("Resources1.resources");

// Instantiate a standalone .resources file from a stream.
var fs = new System.IO.FileStream(@".\Resources2.resources",
                                  System.IO.FileMode.Open);
var rr2 = new System.Resources.ResourceReader(fs);

' Instantiate a standalone .resources file from its filename.
Dim rr1 As New System.Resources.ResourceReader("Resources1.resources")

' Instantiate a standalone .resources file from a stream.
Dim fs As New System.IO.FileStream(".\Resources2.resources",
                                   System.IO.FileMode.Open)
Dim rr2 As New System.Resources.ResourceReader(fs)

To create a ResourceReader object that represents an embedded .resources file, instantiate an Assembly object from the assembly in which the .resources file is embedded. Its Assembly.GetManifestResourceStream method returns a Stream object that can be passed to the ResourceReader(Stream) constructor. The following example instantiates a ResourceReader object that represents an embedded .resources file.

System.Reflection.Assembly assem =
             System.Reflection.Assembly.LoadFrom(@".\MyLibrary.dll");
System.IO.Stream fs =
             assem.GetManifestResourceStream("MyCompany.LibraryResources.resources");
var rr = new System.Resources.ResourceReader(fs);

Dim assem As System.Reflection.Assembly = 
             System.Reflection.Assembly.LoadFrom(".\MyLibrary.dll") 
Dim fs As System.IO.Stream = 
             assem.GetManifestResourceStream("MyCompany.LibraryResources.resources")
Dim rr As New System.Resources.ResourceReader(fs)

Enumerate a ResourceReader object's resources

To enumerate the resources in a .resources file, you call the GetEnumerator method, which returns an System.Collections.IDictionaryEnumerator object. You call the IDictionaryEnumerator.MoveNext method to move from one resource to the next. The method returns false when all the resources in the .resources file have been enumerated.

You can retrieve the individual resources in the collection in two ways:

• You can iterate each resource in the System.Collections.IDictionaryEnumerator collection and use System.Collections.IDictionaryEnumerator properties to retrieve the resource name and value. We recommend this technique when all the resources are of the same type, or you know the data type of each resource.

• You can retrieve the name of each resource when you iterate the System.Collections.IDictionaryEnumerator collection and call the GetResourceData method to retrieve the resource's data. We recommend this approach when you do not know the data type of each resource or if the previous approach throws exceptions.

Retrieve resources by using IDictionaryEnumerator properties

The first method of enumerating the resources in a .resources file involves directly retrieving each resource's name/value pair. After you call the IDictionaryEnumerator.MoveNext method to move to each resource in the collection, you can retrieve the resource name from the IDictionaryEnumerator.Key property and the resource data from the IDictionaryEnumerator.Value property.

The following example shows how to retrieve the name and value of each resource in a .resources file by using the IDictionaryEnumerator.Key and IDictionaryEnumerator.Value properties. To run the example, create the following text file named ApplicationResources.txt to define string resources.

Title="Contact Information"
Label1="First Name:"
Label2="Middle Name:"
Label3="Last Name:"
Label4="SSN:"
Label5="Street Address:"
Label6="City:"
Label7="State:"
Label8="Zip Code:"
Label9="Home Phone:"
Label10="Business Phone:"
Label11="Mobile Phone:"
Label12="Other Phone:"
Label13="Fax:"
Label14="Email Address:"
Label15="Alternate Email Address:"

You can then convert the text resource file to a binary file named ApplicationResources.resources by using the following command:

resgen ApplicationResources.txt

The following example then uses the ResourceReader class to enumerate each resource in the standalone binary .resources file and to display its key name and corresponding value.

using System;
using System.Collections;
using System.Resources;

public class Example1
{
   public static void Run()
   {
      Console.WriteLine("Resources in ApplicationResources.resources:");
      ResourceReader res = new ResourceReader(@".\ApplicationResources.resources");
      IDictionaryEnumerator dict = res.GetEnumerator();
      while (dict.MoveNext())
         Console.WriteLine("   {0}: '{1}' (Type {2})", 
                           dict.Key, dict.Value, dict.Value.GetType().Name);
      res.Close();
   }
}
// The example displays the following output:
//       Resources in ApplicationResources.resources:
//          Label3: '"Last Name:"' (Type String)
//          Label2: '"Middle Name:"' (Type String)
//          Label1: '"First Name:"' (Type String)
//          Label7: '"State:"' (Type String)
//          Label6: '"City:"' (Type String)
//          Label5: '"Street Address:"' (Type String)
//          Label4: '"SSN:"' (Type String)
//          Label9: '"Home Phone:"' (Type String)
//          Label8: '"Zip Code:"' (Type String)
//          Title: '"Contact Information"' (Type String)
//          Label12: '"Other Phone:"' (Type String)
//          Label13: '"Fax:"' (Type String)
//          Label10: '"Business Phone:"' (Type String)
//          Label11: '"Mobile Phone:"' (Type String)
//          Label14: '"Email Address:"' (Type String)
//          Label15: '"Alternate Email Address:"' (Type String)

Imports System.Collections
Imports System.Resources

Module Example2
    Public Sub Main()
        Console.WriteLine("Resources in ApplicationResources.resources:")
        Dim res As New ResourceReader(".\ApplicationResources.resources")
        Dim dict As IDictionaryEnumerator = res.GetEnumerator()
        Do While dict.MoveNext()
            Console.WriteLine("   {0}: '{1}' (Type {2})", dict.Key, dict.Value, dict.Value.GetType().Name)
        Loop
        res.Close()
    End Sub
End Module
' The example displays output like the following:
'       Resources in ApplicationResources.resources:
'          Label3: '"Last Name:"' (Type String)
'          Label2: '"Middle Name:"' (Type String)
'          Label1: '"First Name:"' (Type String)
'          Label7: '"State:"' (Type String)
'          Label6: '"City:"' (Type String)
'          Label5: '"Street Address:"' (Type String)
'          Label4: '"SSN:"' (Type String)
'          Label9: '"Home Phone:"' (Type String)
'          Label8: '"Zip Code:"' (Type String)
'          Title: '"Contact Information"' (Type String)
'          Label12: '"Other Phone:"' (Type String)
'          Label13: '"Fax:"' (Type String)
'          Label10: '"Business Phone:"' (Type String)
'          Label11: '"Mobile Phone:"' (Type String)
'          Label14: '"Email Address:"' (Type String)
'          Label15: '"Alternate Email Address:"' (Type String)

The attempt to retrieve resource data from the IDictionaryEnumerator.Value property can throw the following exceptions:

• A FormatException if the data is not in the expected format.
• A FileNotFoundException if the assembly that contains the type to which the data belongs cannot be found.
• A TypeLoadException if the type to which the data belongs cannot be cannot be found.

Typically, these exceptions are thrown if the .resources file has been modified manually, if the assembly in which a type is defined has either not been included with an application or has been inadvertently deleted, or if the assembly is an older version that predates a type. If one of these exceptions is thrown, you can retrieve resources by enumerating each resource and calling the GetResourceData method, as the following section shows. This approach provides you with some information about the data type that the IDictionaryEnumerator.Value property attempted to return.

Retrieve resources by name with GetResourceData

The second approach to enumerating resources in a .resources file also involves navigating through the resources in the file by calling the IDictionaryEnumerator.MoveNext method. For each resource, you retrieve the resource's name from the IDictionaryEnumerator.Key property, which is then passed to the GetResourceData(String, String, Byte[]) method to retrieve the resource's data. This is returned as a byte array in the resourceData argument.

This approach is more awkward than retrieving the resource name and value from the IDictionaryEnumerator.Key and IDictionaryEnumerator.Value properties, because it returns the actual bytes that form the resource value. However, if the attempt to retrieve the resource throws an exception, the GetResourceData method can help identify the source of the exception by supplying information about the resource's data type. For more information about the string that indicates the resource's data type, see GetResourceData.

The following example illustrates how to use this approach to retrieve resources and to handle any exceptions that are thrown. It programmatically creates a binary .resources file that contains four strings, one Boolean, one integer, and one bitmap. To run the example, do the following:

1. Compile and execute the following source code, which creates a .resources file named ContactResources.resources.

   using System.Drawing;
   using System.Drawing.Imaging;
   using System.IO;
   using System.Resources;
   using System.Runtime.Versioning;
   
   public class Example5
   {
       [SupportedOSPlatform("windows")]
       public static void Run()
       {
           // Bitmap as stream.
           MemoryStream bitmapStream = new MemoryStream();
           Bitmap bmp = new Bitmap(@".\ContactsIcon.jpg");
           bmp.Save(bitmapStream, ImageFormat.Jpeg);
   
           // Define resources to be written.
           using (ResourceWriter rw = new ResourceWriter(@".\ContactResources.resources"))
           {
               rw.AddResource("Title", "Contact List");
               rw.AddResource("NColumns", 5);
               rw.AddResource("Icon", bitmapStream);
               rw.AddResource("Header1", "Name");
               rw.AddResource("Header2", "City");
               rw.AddResource("Header3", "State");
               rw.AddResource("ClientVersion", true);
               rw.Generate();
           }
       }
   }
   

   The source code file is named CreateResources.cs. You can compile it in C# by using the following command:

   csc CreateResources.cs /r:library.dll
   

2. Compile and run the following code to enumerate the resources in the ContactResources.resources file.

   using System;
   using System.Collections;
   using System.Drawing;
   using System.IO;
   using System.Resources;
   using System.Runtime.Versioning;
   
   public class Example6
   {
       [SupportedOSPlatform("windows")]
       public static void Run()
       {
           ResourceReader rdr = new ResourceReader(@".\ContactResources.resources");
           IDictionaryEnumerator dict = rdr.GetEnumerator();
           while (dict.MoveNext())
           {
               Console.WriteLine("Resource Name: {0}", dict.Key);
               try
               {
                   Console.WriteLine("   Value: {0}", dict.Value);
               }
               catch (FileNotFoundException)
               {
                   Console.WriteLine("   Exception: A file cannot be found.");
                   DisplayResourceInfo(rdr, (string)dict.Key, false);
               }
               catch (FormatException)
               {
                   Console.WriteLine("   Exception: Corrupted data.");
                   DisplayResourceInfo(rdr, (string)dict.Key, true);
               }
               catch (TypeLoadException)
               {
                   Console.WriteLine("   Exception: Cannot load the data type.");
                   DisplayResourceInfo(rdr, (string)dict.Key, false);
               }
           }
       }
   
       [SupportedOSPlatform("windows")]
       private static void DisplayResourceInfo(ResourceReader rr,
                                       string key, bool loaded)
       {
           string dataType = null;
           byte[] data = null;
           rr.GetResourceData(key, out dataType, out data);
   
           // Display the data type.
           Console.WriteLine("   Data Type: {0}", dataType);
           // Display the bytes that form the available data.      
           Console.Write("   Data: ");
           int lines = 0;
           foreach (var dataItem in data)
           {
               lines++;
               Console.Write("{0:X2} ", dataItem);
               if (lines % 25 == 0)
                   Console.Write("\n         ");
           }
           Console.WriteLine();
           // Try to recreate current state of data.
           // Do: Bitmap, DateTimeTZI
           switch (dataType)
           {
               // Handle internally serialized string data (ResourceTypeCode members).
               case "ResourceTypeCode.String":
                   BinaryReader reader = new BinaryReader(new MemoryStream(data));
                   string binData = reader.ReadString();
                   Console.WriteLine("   Recreated Value: {0}", binData);
                   break;
               case "ResourceTypeCode.Int32":
                   Console.WriteLine("   Recreated Value: {0}",
                                     BitConverter.ToInt32(data, 0));
                   break;
               case "ResourceTypeCode.Boolean":
                   Console.WriteLine("   Recreated Value: {0}",
                                     BitConverter.ToBoolean(data, 0));
                   break;
               // .jpeg image stored as a stream.
               case "ResourceTypeCode.Stream":
                   const int OFFSET = 4;
                   int size = BitConverter.ToInt32(data, 0);
                   Bitmap value1 = new Bitmap(new MemoryStream(data, OFFSET, size));
                   Console.WriteLine("   Recreated Value: {0}", value1);
                   break;
               default:
                   break;
           }
           Console.WriteLine();
       }
   }
   

   After modifying the source code (for example, by deliberately throwing a FormatException at the end of the try block), you can run the example to see how calls to GetResourceData enable you to retrieve or recreate some resource information.