.NET 1.1+

Recycling Files and Folders Part 2

The second part of this two-part article revisits sending files and folders to the Windows Recycle Bin. In the first part we used the VisualBasic namespace to perform this task. In the second part we will make use of the Windows API through P/Invoke.

P/Invoke

The first instalment of this article examined the methods available for sending files and folders to the Recycle Bin using the FileSystem class in the Microsoft.VisualBasic.FileIO namespace. This provided a method of recycling files, rather than deleting them, using purely managed code.

In this part of the article we will look at a second method for using the Recycle Bin. This will utilise Platform Invocation Services (P/Invoke) to call functions in the Windows API. This provides a more complex manner of recycling files and folders that can be used when the more limited functionality of the FileSystem class is not suitable.

As we are using P/Invoke, it is useful to include the following using directive in the code:

SHFileOperation Function

The Windows API function that is used for file operations such as deleting files and folders, or for sending them to the Recycle Bin, is named "SHFileOperation". The function is found in the shell32 dynamic linked library (DLL). To declare a reference to this function so that you may call it from managed code, include the following inside the code block of your class:

[DllImport("Shell32.dll")]
static extern int SHFileOperation([In] ref SHFILEOPSTRUCT lpFileOp);

The function accepts a single parameter containing the details of the operation to be carried out. This parameter is a structure containing eight fields, some of which are required and others that we will not use. The fields that we will utilise in this article are:

• wFunc. This field determines the type of operation that will be executed. Various operations are available to allow copying, renaming, moving and deleting files. We will use the function name "FO_DELETE", which allows files and folders to be deleted or recycled.
• pFrom. This field specifies the name of the file or folder to be deleted. It is a double null-terminated string that should contain the full path of the file or folder.
• fFlags. This field specifies a set of flags that modify the behaviour of the file operation. There are several flags that can be combined with logical bitwise operators when recycling files and folders. We can define some of them as constants, as well as declaring the structure itself, using the following code within the class:

[StructLayout(LayoutKind.Sequential)]
public struct SHFILEOPSTRUCT
{
    public IntPtr hwnd;
    public uint wFunc;
    public string pFrom;
    public string pTo;
    public ushort fFlags;
    public int fAnyOperationsAborted;
    public IntPtr hNameMappings;
    [MarshalAs(UnmanagedType.LPWStr)]
    public string lpszProgressTitle; 
}

private const int FO_DELETE = 0x0003;
private const int FOF_SILENT = 0x0004;
private const int FOF_ALLOWUNDO = 0x0040;
private const int FOF_NOCONFIRMATION = 0x0010;
private const int FOF_WANTNUKEWARNING = 0x4000;

In addition to the parameters, the SHFileOperation function returns an integer value. If the value is zero, the operation was successful. If it is any other value, an error occurred during the operation. The value returned is the error code that describes the problem. For more details about error codes, review the documentation provided by MSDN.