OnDisposeStream

The abstract base class Stream supports reading and writing bytes. All classes that represent streams inherit from the Stream class. The Stream class and its derived classes provide a common view of data sources and repositories, and isolate the programmer from the specific details of the operating system and underlying devices.

OnDisposeStream enables you to wrap a stream and supply an action to be carried out when the underlying stream is closed. This is useful for situations whereby a Stream is created from a resource, and you want to be able to clean up that resource when the Stream is closed.

Use this component

If you have not already added it to your project, install the package from NuGet:

Install-Package NetEx.IO

Use the OnDisposeStream constructor to create a OnDisposeStream instance that wraps another Stream, supplying an action to be invoked when that stream is closed. You can then use the OnDisposeStream instance wherever you can use a Stream.

Example

The following example uses the Windows Forms Button control's Click event handler to create a ZipArchive, which is saved in a MemoryStream, and contains a single text file.

The ZipArchive is then opened in a separate OpenZip method, and the compressed file returned as an OnDisposeStream. The contents of the compressed file are displayed in a MessageBox, and the OnDisposeStream is then closed. When the OnDisposeStream is closed, it will also close the ZipArchive and show a MessageBox.

Note

In the below example, the method to open a compressed file within the zip file (OpenZip) is within the same class as the code that consumes the compressed file. So in this scenario it would be easy to close the zip file directly.

However, in a real-world scenario the method to return the compressed file may be contained in a library, and as a maintainer of the library you may wish to ensure that all resources you use are cleaned up. To do so you could return an OnDisposeStream instance, which would ensure that, when the consumer of your library is finished with the compressed file, you are able to clean up any resources you used.

using NetEx.IO;
using System;
using System.IO;
using System.IO.Compression;
using System.Windows.Forms;

public class OnDisposeStreamForm : Form
{
    [STAThread]
    public static void Main()
    {
        Application.SetCompatibleTextRenderingDefault(false);
        Application.EnableVisualStyles();
        Application.Run(new OnDisposeStreamForm());
    }

    private Button selectButton;

    public OnDisposeStreamForm()
    {
        selectButton = new Button
        {
            Size = new Size(100, 20),
            Location = new Point(15, 15),
            Text = "Read OnDisposeStream"
        };
        selectButton.Click += new EventHandler(SelectButton_Click);
        ClientSize = new Size(330, 360);
        Controls.Add(selectButton);
    }

    private void SelectButton_Click(object sender, EventArgs e)
    {
        // Store data in a byte array instead of creating temporary files
        var data = new byte[256];

        // Create a zip file containing a "Hello World!" text file
        using (var zipFileStream = new MemoryStream(data))
        {
            using (var zipFile = new ZipArchive(zipFileStream, ZipArchiveMode.Create))
            {
                var compressedFile = zipFile.CreateEntry("TextFile.txt");
                using (var compressedFileStream = compressedFile.Open())
                {
                    using (var compressedFileStreamWriter = new StreamWriter(compressedFileStream))
                    {
                        compressedFileStreamWriter.Write("Hello World!");
                    }
                }
            }
        }

        // Now open the zip file and read the text file
        using (var zipFileStream = new MemoryStream(data))
        {
            using (var streamReader = new StreamReader(OpenZip(zipFileStream)))
            {
                MessageBox.Show(streamReader.ReadLine());
            }
        }
    }

    private Stream OpenZip(Stream zipFileStream)
    {
        var zipFile = new ZipArchive(zipFileStream, ZipArchiveMode.Read);
        var compressedFile = zipFile.GetEntry("TextFile.txt");
        return new OnDisposeStream(compressedFile!.Open(), b =>
        {
            zipFile.Dispose();
            MessageBox.Show("Zip file disposed!");
        });
    }
}

Applies to

Product	Versions
.NET	5, 6, 7, 8, 9
.NET Framework	2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard	2.0, 2.1

See also

Files and Stream I/O

Acknowledgements

Credit goes to craftworkgames for the original idea and implementation of OnDisposeStream.