How to embed and access resources by using Visual Basic .NET or Visual Basic 2005

For a Microsoft C# .NET version of this article, see
319292 .
For a Microsoft Visual Basic 6.0 version of this article, see
205332 .

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Summary

This step-by-step article describes how to use Microsoft Visual Basic .NET or Microsoft Visual Basic 2005 to embed resources as part of the assembly, and then access the resources at run time.

Overview

The .NET Framework can encapsulate files as part of a compiled assembly. These files are known as embedded resources. These resources are completely separate from the .resources and .resx files that are associated with the assembly. You can access these resources at run time through the Assembly class of the System.Reflection namespace.

A major advantage of embedding resources to the Manifest is that because the files are part of your compiled assembly, the user cannot accidentally delete or misplace files that are critical to your application, which in some cases may prevent the execution of your program. One limitation of this approach is that you cannot save any changes to this file to the assembly without recompiling the program. Because of this, only include files that will not change during the lifetime of your application as an embedded resource.

Step-by-step demonstration

To add embedded resources to your project, you must first add the files as part of your project. After you have added the files to your project, you can access and display the resources through the System.Reflection namespace.

Add embedded resources

To add a text file and an image file to your project as embedded resources, follow these steps:
  1. Create a new Windows Application project for this demonstration. This form is used to display the resources that are accessed from the executing assembly during run time.
  2. Right-click your project name, click Add, and then click Add New Item.
  3. In the New Item dialog box, select Text File from the menu, and name the file MyTextFile.txt. When the file opens in the integrated development environment (IDE), add some text, and then close the file.
  4. Repeat steps 1 and 2 to add a bitmap image to your project, but instead of selecting Text File as the new item type, select Bitmap File, and then change the file name to MyImage.bmp. When the new image is opened in the IDE, draw something on the image, and then close the file.
  5. Right-click either the text file or the bitmap, and then select Properties.
  6. In the Properties dialog box, locate the Build Action property. By default, this property is set to Content. Click the property and change the Build Action property to Embedded Resource.
  7. Repeat steps 4 and 5 for the other file.
The next time you build the project, the compiler adds these files to your assembly. The compiler adds the root namespace of the project to the name of the resource when it is included in the project. For example, if the root namespace of your project is MyNamespace, the resources are named MyNamespace.MyTextFile.txt and MyNamespace.MyImage.bmp.

Note The resource file names are case-sensitive. When you access the resources, you must use the exact spelling and case of the file name. If you do not use the exact spelling and case of the file name, the method call to access the ManifestResourceStream returns Nothing, and the system does not raise an exception.

Note If you want to verify the resource names, you can use the Microsoft Intermediate Language Disassembler (ILDASM) to view the Manifest data, which lists the included resources.

Access resources

To access the resources that you have embedded in the Manifest of your assembly, import the System.IO and the System.Reflection namespaces, as follows:
   Imports System.IO
Imports System.Reflection
The System.IO namespace provides the definition of a stream and the System.Reflection namespace defines the Assembly class that provides methods to access the resources that are embedded in your assembly.

When you declare the following in the general declaration area, the resources from the assembly are read when the form is loaded:
   Dim _imageStream As Stream
Dim _textStreamReader As StreamReader
Dim _assembly As [Assembly]
Note To access the Load event for the form in the Code Editor, double-click the form in the Design Editor.

To read the resource from the assembly that is executing the current code, you must obtain an instance of that assembly. To do this, use the GetExecutingAssembly method of the assembly, as follows:
   _assembly = [Assembly].GetExecutingAssembly()
Reading the information from the resource to a stream is performed with a method call to GetManifestResourceStream. The parameter that is passed to this method is the name of the resource that is to be accessed. The two resources are then read to their corresponding streams as the Load event of the form is executed.
   _imageStream =  _assembly.GetManifestResourceStream("MyNameSpace.MyImage.bmp")
_textStreamReader = new StreamReader(_assembly.GetManifestResourceStream("MyNameSpace.MyTextFile.txt"))
The code in the Load event for the form resembles the following:
   Try
_assembly = [Assembly].GetExecutingAssembly()
_imageStream = _assembly.GetManifestResourceStream("MyNameSpace.MyImage.bmp")
_textStreamReader = New StreamReader(_assembly.GetManifestResourceStream("MyNamespace.MyTextFile.txt"))
Catch ex As Exception
MessageBox.Show("Resource wasn't found!", "Error")
End Try
The Try-Catch statement, known as structured error handling in .NET, is used to catch any errors that may have occurred while the instance of the Assembly class accesses the resources.

Display resources

This example uses two buttons to display the embedded resources. When you click the first button, a bitmap image that is based on the resource that is read from the assembly is created and displayed in the PictureBox control of the form. The second button reads from a text resource and displays the text in a text box.

To display the embedded resources, follow these steps:
  1. Add a PictureBox control to the form.
  2. Add a new Button control to the form, and then change its Text property to Show Image.
  3. Double-click the button to open its Click event in the code viewer, and then paste the following code in this event:
       Try
    PictureBox1.Image = New Bitmap(_imageStream)
    Catch ex As Exception
    MessageBox.Show("Image Couldn't be created !")
    End Try
    This code generates a new instance of a bitmap that is based on the resource stream that was read in the Load event of the form.

  4. Add a TextBox control to the form.
  5. Add another Button control to the form, and then change its Text property to Get Text.
  6. Double-click the button in the Design Editor to open the Click_Event for the button, and then paste the following code in the event:
       Try
    If _textStreamReader.Peek() <> -1 Then
    TextBox1.Text = _textStreamReader.ReadLine()
    End If
    Catch ex As Exception
    MessageBox.Show("Error reading stream!")
    End Try
    This code determines whether characters to be read still exist in the stream. If characters are found, a line is read to the text box.
  7. Press F5 to run the application.

Full code

   Imports System.IO
Imports System.Reflection

Public Class Form1
Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

Public Sub New()
MyBase.New()

'This call is required by the Windows Form Designer.
InitializeComponent()

'Add any initialization after the InitializeComponent() call.
End Sub

'Form overrides dispose to clean up the component list.
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Dispose()
End If
End If
MyBase.Dispose(disposing)
End Sub

'Required by the Windows Form Designer.
Private components As System.ComponentModel.IContainer

'NOTE: The following procedure is required by the Windows Form Designer.
'It can be modified using the Windows Form Designer.
'Do not modify it using the code editor.
Friend WithEvents Button1 As System.Windows.Forms.Button
Friend WithEvents PictureBox1 As System.Windows.Forms.PictureBox
Friend WithEvents Button2 As System.Windows.Forms.Button
Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
Me.Button1 = New System.Windows.Forms.Button()
Me.PictureBox1 = New System.Windows.Forms.PictureBox()
Me.Button2 = New System.Windows.Forms.Button()
Me.TextBox1 = New System.Windows.Forms.TextBox()
Me.SuspendLayout()
'
'Button1
'
Me.Button1.Location = New System.Drawing.Point(16, 196)
Me.Button1.Name = "Button1"
Me.Button1.TabIndex = 0
Me.Button1.Text = "Show Image"
'
'PictureBox1
'
Me.PictureBox1.Location = New System.Drawing.Point(8, 8)
Me.PictureBox1.Name = "PictureBox1"
Me.PictureBox1.Size = New System.Drawing.Size(280, 184)
Me.PictureBox1.TabIndex = 1
Me.PictureBox1.TabStop = False
'
'Button2
'
Me.Button2.Location = New System.Drawing.Point(16, 232)
Me.Button2.Name = "Button2"
Me.Button2.TabIndex = 2
Me.Button2.Text = "Get Text"
'
'TextBox1
'
Me.TextBox1.Location = New System.Drawing.Point(100, 232)
Me.TextBox1.Name = "TextBox1"
Me.TextBox1.Size = New System.Drawing.Size(176, 20)
Me.TextBox1.TabIndex = 3
Me.TextBox1.Text = "TextBox1"
'
'Form1
'
Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
Me.ClientSize = New System.Drawing.Size(292, 266)
Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.TextBox1, Me.Button2, Me.PictureBox1, Me.Button1})
Me.Name = "Form1"
Me.Text = "Form1"
Me.ResumeLayout(False)

End Sub

#End Region

Dim _imageStream As Stream
Dim _textStreamReader As StreamReader
Dim _assembly As [Assembly]

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Try
_assembly = [Assembly].GetExecutingAssembly()
_imageStream = _assembly.GetManifestResourceStream("MyNamespace.MyImage.bmp")
_textStreamReader = New StreamReader(_assembly.GetManifestResourceStream("MyNamespace.MyTextFile.txt"))
Catch ex As Exception
MessageBox.Show("Resource wasn't found!", "Error")
End Try
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Try
PictureBox1.Image = New Bitmap(_imageStream)
Catch ex As Exception
MessageBox.Show("Image Couldn't be created !")
End Try
End Sub

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
Try
If _textStreamReader.Peek() <> -1 Then
TextBox1.Text = _textStreamReader.ReadLine()
End If
Catch ex As Exception
MessageBox.Show("Error reading stream!")
End Try
End Sub
End Class
Note The code should be changed in Visual Basic 2005. If you create a new form that is named Form1 in Visual Basic 2005, a Form1.vb file is created for your code and a Form1.Designer.vb file is created that contains the automatically generated part. The Windows Forms Designer uses the partial keyword to divide the implementation of Form1 into two separate files. This prevents the designer-emitted code from being interspersed with your code.



For more information about the new Visual Basic 2005 language enhancements, visit the following Microsoft Developer Network (MSDN) Web site:


For more information about partial classes and the Windows Forms Designer, visit the following MSDN Web site:

Troubleshooting

Because resource names are case-sensitive, verify that you are using the correct spelling and case of the resources that are accessed. You can use ILDASM to read the Manifest data to verify the exact spelling of the resources.

References

Propiedades

Id. de artículo: 319291 - Última revisión: 16 may. 2007 - Revisión: 1

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