File Association Properties

Is there an API function that will allow me to retrieve the file association details for a given file extension ? I want to know what type of file is being drag-dropped onto my application and how to launch that file ( including shortcuts).

Any help on this one would be much appreciated.

I don't know of any api that retrieves the properties you are looking for, but should be able to get some information from the registry. In case you don't have the code to get and set regvalues, I post it here. It is a rather long article from Microsoft's site, so I first want to make some notes:

Run the program regedit.exe from your windows folder in order to view the registry. A lot of info is in the registry but beware that changing it can be rather dangerous.

File association info and similar is in "hkey_classes_root\.ext" where ext is the extension. .bat for example has a default value leading to "batfile". "batfile" a good scroll down the list has some keys and values, that you should be able to use.

I haven't tried it myself and I haven't tried the code below, so I can't help you much more than this. Hope it's enough.



HOWTO: Use the Registry API to Save and Retrieve Setting
The information in this article applies to:
Microsoft Visual Basic Professional and Enterprise Editions for Windows, version 5.0
Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 16-bit and 32-bit, for Windows, version 4.0


SUMMARY
Although Visual Basic includes the SaveSetting and GetSetting functions to save and retrieve information from the registry, these functions only operate on a specific section of the registry, the Visual Basic and VBA Program Settings of the HKEY_CURRENT_USER root key.

This article outlines the use of 32-bit Windows API functions, which can be used to set and retrieve values from anywhere in the registry. The topics and function references in this article can be generalized to program the 16-bit registry.

The 32-bit API functions also include support for security, although an overview of security is outside the scope of this article.

NOTE: The SaveSetting and GetSetting functions are not part of the VBA function library. However, the sample code below still applies to 32-bit applications that implement VBA.



MORE INFORMATION


General Registry Information
The registry is used by applications and Windows to store configuration data. It is a replacement for the large numbers of INI files that proliferated on Windows 3.x machines and is also used heavily by OLE.

The registry is organized using a hierarchical series of keys and values resembling a tree. Each key, beginning with one of the six predefined root keys, can have sub-keys and values associated with it. The keys are organizational and naming units and appear in the Windows Registry Editors as file folders. Values are data entries and appear as text entries in the right pane of the Registry Editor window. Keys need not have any associated values, but may have many. Each value has an associated data type. The two most commonly used registry data types are REG_SZ, a null-terminated string; and REG_DWORD, a 32-bit number.

The basic process used to write or read from a location in the registry is the same. To reference any given key or value, you must have a handle to the key. Once this handle is obtained, values and sub-keys of the key that this handle refers to can be read, set, or listed (enumerated).

Given a location in the registry, to obtain a handle to that key, you must begin with one of the six predefined keys (HKEY_CLASSES_ROOT, HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE, HKEY_USERS, HKEY_CURRENT_CONFIG, and HKEY_DYN_DATA) and traverse the registry tree until the desired key is reached. User programs most often read and write from HKEY_CURRENT_USER and HKEY_LOCAL_MACHINE. If the keys being traversed exist already, you can use a series of calls to the RegOpenKey or RegOpenKeyEx functions. If the keys need to be created, the RegCreateKey and RegCreateKeyEx functions do the job.

With the handle to the desired key, the functions used to list, set, and retrieve information can be called. In all cases, the functions with the Ex suffix will work only on 32-bit platforms. Functions without the suffix may work on both 16-bit and 32-bit versions of Windows. Keep in mind that not all registry functions lacking the 'Ex' suffix are functions provided for 16-bit compatibility. The Ex suffix was only added when the capabilities of 16-bit functions were expanded. Functions that are totally new and specific to 32-bit platforms do not possess an Ex extension.

The RegSetValue and RegSetValueEx functions allow the settings of a value to be modified, while RegQueryValue and RegQueryValueEx retrieve the current setting of a value. The limitations of the non-Ex, 16-bit versions of these APIs are very evident here. When using the 16-bit RegSetValue function there is no way to name a value, and because of this, RegSetValue can't be used to associate more than one value with each key. In addition, all values written with RegSetValue have a data type of REG_SZ. These limitations are inherent with the 16-bit Registry. RegSetValueEx allows the creation of a multiple number of values with any available data type.



How to Write to a Specific Registry Location
After determining what functions you will need to use for your project, copy the relevant declares from the code at the end of this article to a basic module. The two Visual Basic procedures included (SetValueEx and QueryValueEx) are wrappers for the RegSetValueEx and RegQueryValueEx API functions and greatly simplify their use. The notes below make use of these Visual Basic functions; however, you are free to make calls directly to the API if you wish.

Creating/Modifying Keys and Values:

With the declarations and procedures available, you can create and open keys, and add, modify, and read values. The three following sections explain how to create a key, set or modify a value, and query a value.

Creating a New Key:

Creating a new key is as simple as using the following procedure. CreateNewKey takes the name of the key to create, and the constant representing the predefined key to create the key under. The call to RegCreateKeyEx doesn't take advantage of the security mechanisms allowed, but could be modified to do so. A discussion of Registry security is outside the scope of this article.

Code:

---

  Private Sub CreateNewKey (sNewKeyName As String, lPredefinedKey As Long)
      Dim hNewKey As Long        'handle to the new key
      Dim lRetVal As Long        'result of the RegCreateKeyEx function

      lRetVal = RegCreateKeyEx(lPredefinedKey, sNewKeyName, 0&, _
                vbNullString, REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, _
                0&, hNewKey, lRetVal)
      RegCloseKey (hNewKey)
  End Sub

With this procedure a call of:

  CreateNewKey "TestKey", HKEY_CURRENT_USER

---

will create a key called TestKey immediately under HKEY_CURRENT_USER.
Calling CreateNewKey like this:

Code:

---

      CreateNewKey "TestKey\SubKey1\SubKey2", HKEY_LOCAL_MACHINE

---

will create three-nested keys beginning with TestKey immediately under HKEY_LOCAL_MACHINE, SubKey1 subordinate to TestKey, and SubKey3 under SubKey2.
Setting/Modifying a Value:

Creating and setting a value of a specified key can be accomplished with the following short procedure. SetKeyValue takes the key that the value will be associated with, the name of the value, the setting of the value, and the type of the value (the SetValueEx function only supports REG_SZ and REG_DWORD, but this can be modified if necessary). Specifying a new value for an existing sValueName will modify the current setting of that value.

Code:

---

  Private Sub SetKeyValue (sKeyName As String, sValueName As String, _
  vValueSetting As Variant, lValueType As Long)
      Dim lRetVal As Long        'result of the SetValueEx function
      Dim hKey As Long        'handle of open key

      'open the specified key
      lRetVal = RegOpenKeyEx(HKEY_CURRENT_USER, sKeyName, 0, _
                              KEY_ALL_ACCESS, hKey)
      lRetVal = SetValueEx(hKey, sValueName, lValueType, vValueSetting)
      RegCloseKey (hKey)
  End Sub

A call of:

  SetKeyValue "TestKey\SubKey1", "StringValue", "Hello", REG_SZ

---

will create a value of type REG_SZ called "SubKey1" with the setting of "Hello." This value will be associated with the key SubKey1 of "TestKey."
In this case, "TestKey" is a subkey of HKEY_CURRENT_USER, but this can be modified by changing the call to RegOpenKeyEx. This call will fail if "TestKey\SubKey1" does not exist. To avoid this problem, use a call to RegCreateKeyEx instead of a call to RegOpenKeyEx. RegCreateKeyEx will open a specified key if it already exists.

Querying a Value:

The next procedure can be used to ascertain the setting of an existing value. QueryValue takes the name of the key and the name of a value associated with that key and displays a message box with the corresponding value. It uses a call to the QueryValueEx wrapper function defined below, that only supports REG_SZ and REG_DWORD types.

Code:

---

  Private Sub QueryValue (sKeyName As String, sValueName As String)
      Dim lRetVal As Long        'result of the API functions
      Dim hKey As Long        'handle of opened key
      Dim vValue As Variant      'setting of queried value

      lRetVal = RegOpenKeyEx(HKEY_CURRENT_USER, sKeyName, 0, _
  KEY_ALL_ACCESS, hKey)
      lRetVal = QueryValueEx(hKey, sValueName, vValue)
      MsgBox vValue
      RegCloseKey (hKey)
  End Sub

With this procedure, a call of:

  QueryValue "TestKey\SubKey1", "StringValue"

---

will display a message box with the current setting of the "StringValue" value, and assumes that "StringValue" exists in the "TestKey\SubKey1" key.
If the Value that you query does not exist then QueryValue will return an error code of 2 - 'ERROR_BADKEY'.

Additional Notes:

The above examples use the extended 32-bit versions of the registry functions exclusively. These functions allow more than one value to be associated with each key. As discussed above, the 16-bit RegSetValue and RegQueryValue act on a single value associated with the current key (which is always of the type REG_SZ). These functions appear in the 32-bit Registry Editor with a name of <NO NAME>. To set, modify, or query this special associated value, one must use the 16-bit registry functions. Reading and writing from the registry in a 16-bit environment is much simpler than in a 32-bit environment. The same basic procedure is followed: open a key and get a handle and then call your modification function with that handle, but no consideration needs to be made for multiple associated values or for different value data types. A 16-bit application can create and modify keys and values with the declarations of the RegCreateKey, RegOpenKey, RegQueryValue, RegSetValue, and RegCloseKey functions.

In some cases, there is no need for any values to be associated with a key. An application may only need to know if a certain key or value exists, and not care about the nature of the key's values. In a situation like this, the RegEnumKey, RegEnumKeyEx, and RegEnumValue functions can be used to determine whether a certain key or value exists. For more information on these functions refer to the API Text Viewer and/or Windows API reference.

Code:

---

API Function and Constant Declarations

  Option Explicit

  Public Const REG_SZ As Long = 1
  Public Const REG_DWORD As Long = 4

  Public Const HKEY_CLASSES_ROOT = &H80000000
  Public Const HKEY_CURRENT_USER = &H80000001
  Public Const HKEY_LOCAL_MACHINE = &H80000002
  Public Const HKEY_USERS = &H80000003

  Public Const ERROR_NONE = 0
  Public Const ERROR_BADDB = 1
  Public Const ERROR_BADKEY = 2
  Public Const ERROR_CANTOPEN = 3
  Public Const ERROR_CANTREAD = 4
  Public Const ERROR_CANTWRITE = 5
  Public Const ERROR_OUTOFMEMORY = 6
  Public Const ERROR_ARENA_TRASHED = 7
  Public Const ERROR_ACCESS_DENIED = 8
  Public Const ERROR_INVALID_PARAMETERS = 87
  Public Const ERROR_NO_MORE_ITEMS = 259

  Public Const KEY_ALL_ACCESS = &H3F

  Public Const REG_OPTION_NON_VOLATILE = 0

  Declare Function RegCloseKey Lib "advapi32.dll" _
  (ByVal hKey As Long) As Long
  Declare Function RegCreateKeyEx Lib "advapi32.dll" Alias _
  "RegCreateKeyExA" (ByVal hKey As Long, ByVal lpSubKey As String, _
  ByVal Reserved As Long, ByVal lpClass As String, ByVal dwOptions _
  As Long, ByVal samDesired As Long, ByVal lpSecurityAttributes _
  As Long, phkResult As Long, lpdwDisposition As Long) As Long
  Declare Function RegOpenKeyEx Lib "advapi32.dll" Alias _
  "RegOpenKeyExA" (ByVal hKey As Long, ByVal lpSubKey As String, _
  ByVal ulOptions As Long, ByVal samDesired As Long, phkResult As _
  Long) As Long
  Declare Function RegQueryValueExString Lib "advapi32.dll" Alias _
  "RegQueryValueExA" (ByVal hKey As Long, ByVal lpValueName As _
  String, ByVal lpReserved As Long, lpType As Long, ByVal lpData _
  As String, lpcbData As Long) As Long
  Declare Function RegQueryValueExLong Lib "advapi32.dll" Alias _
  "RegQueryValueExA" (ByVal hKey As Long, ByVal lpValueName As _
  String, ByVal lpReserved As Long, lpType As Long, lpData As _
  Long, lpcbData As Long) As Long
  Declare Function RegQueryValueExNULL Lib "advapi32.dll" Alias _
  "RegQueryValueExA" (ByVal hKey As Long, ByVal lpValueName As _
  String, ByVal lpReserved As Long, lpType As Long, ByVal lpData _
  As Long, lpcbData As Long) As Long
  Declare Function RegSetValueExString Lib "advapi32.dll" Alias _
  "RegSetValueExA" (ByVal hKey As Long, ByVal lpValueName As String, _
  ByVal Reserved As Long, ByVal dwType As Long, ByVal lpValue As _
  String, ByVal cbData As Long) As Long
  Declare Function RegSetValueExLong Lib "advapi32.dll" Alias _
  "RegSetValueExA" (ByVal hKey As Long, ByVal lpValueName As String, _
  ByVal Reserved As Long, ByVal dwType As Long, lpValue As Long, _
  ByVal cbData As Long) As Long

SetValueEx and QueryValueEx Wrapper Functions:

  Public Function SetValueEx(ByVal hKey As Long, sValueName As String, _
  lType As Long, vValue As Variant) As Long
      Dim lValue As Long
      Dim sValue As String
      Select Case lType
          Case REG_SZ
              sValue = vValue & Chr$(0)
              SetValueEx = RegSetValueExString(hKey, sValueName, 0&, _
                                              lType, sValue, Len(sValue))
          Case REG_DWORD
              lValue = vValue
              SetValueEx = RegSetValueExLong(hKey, sValueName, 0&, _
  lType, lValue, 4)
          End Select
  End Function

  Function QueryValueEx(ByVal lhKey As Long, ByVal szValueName As _
  String, vValue As Variant) As Long
      Dim cch As Long
      Dim lrc As Long
      Dim lType As Long
      Dim lValue As Long
      Dim sValue As String

      On Error GoTo QueryValueExError

      ' Determine the size and type of data to be read
      lrc = RegQueryValueExNULL(lhKey, szValueName, 0&, lType, 0&, cch)
      If lrc <> ERROR_NONE Then Error 5

      Select Case lType
          ' For strings
          Case REG_SZ:
              sValue = String(cch, 0)
  lrc = RegQueryValueExString(lhKey, szValueName, 0&, lType, _
  sValue, cch)
              If lrc = ERROR_NONE Then
                  vValue = Left$(sValue, cch-1)
              Else
                  vValue = Empty
              End If
          ' For DWORDS
          Case REG_DWORD:
  lrc = RegQueryValueExLong(lhKey, szValueName, 0&, lType, _
  lValue, cch)
              If lrc = ERROR_NONE Then vValue = lValue
          Case Else
              'all other data types not supported
              lrc = -1
      End Select

  QueryValueExExit:
      QueryValueEx = lrc
      Exit Function
  QueryValueExError:
      Resume QueryValueExExit
  End Function

---

REFERENCES
Programming the Windows 95 User Interface, Chapter 10 - "Using the Registry"

For function references: Any guide to the Win16 or Win32 API.

Additional query words: registry kbVBp500 kbVBp400 kbWinOS98 kbVBp kbNoKeyWord kbDSupport kbdse

Keywords : kbcode
Technology : kbvba
Version : WINDOWS:4.0,5.0
Platform : WINDOWS
Issue type : kbhowto

Thanks for the info. Martin but I was rather hoping I wouldn't have to search about in the registry for the details. However, if that's what needs to be done then I'll have to do it and the article will be useful. Worth one more plea for help though -

Please, please, please does anyone else know of a nice API which will pull back the information into a structure ? this is my sanity on the line. Registry - brrr.

If you use the Shell API with a filename specified rather than the program, Windows will run the associated program automatically. If you want to know what type of file it is, try the File System Object. If you need to draw the icon in a picture box, try these functions...

Private Declare Function ExtractAssociatedIcon Lib "shell32.dll" Alias "ExtractAssociatedIconA" (ByVal hInst As Long, ByVal lpIconPath As String, lpiIcon As Long) As Long
Private Declare Function DrawIcon Lib "user32" (ByVal hdc As Long, ByVal X As Long, ByVal Y As Long, ByVal hIcon As Long) As Long

Function ShowIcon(ByVal Fnm As String, obj As Object)As Boolean
hIcon = ExtractAssociatedIcon(0, Fnm, 1)
If IsNull(hIcon) Then
ShowIcon = False
Else
DrawIcon obj.hdc, 0, 0, hIcon
ShowIcon = True
End If
End Function

Hope this helps

Big smiles ! Thanks for saving my sanity.