GetObject Function (Visual Basic)

Artikel
11/16/2012

Returns a reference to an object provided by a COM component.

Public Function GetObject( _
    Optional ByVal PathName As String = Nothing, _
    Optional ByVal [Class] As String = Nothing _
) As Object

Parameters

PathName

Optional. String. The full path and name of the file containing the object to retrieve. If PathName is omitted or is a zero-length string (""), Class is required.

Class

Required if PathName is not supplied. String. A string representing the class of the object. The Class argument has the following syntax and parts:

appname.objecttype

Parameter	Description
appname	Required. String. The name of the application providing the object.
objecttype	Required. String. The type or class of object to create.

Exceptions

Exception type	Error number	Condition
Exception	429	No object of the specified class type exists.
FileNotFoundException	432	No object with the specified path and file name exists.

See the "Error number" column if you are upgrading Visual Basic 6.0 applications that use unstructured error handling. (You can compare the error number against the Number Property (Err Object).) However, when possible, you should consider replacing such error control with Structured Exception Handling Overview for Visual Basic.

Remarks

Use the GetObject function to load an instance of a COM component from a file. The following example illustrates this.

Dim CADObject As Object
CADObject = GetObject("C:\CAD\schema.cad")

When this code runs, the application associated with the specified PathName is started and the object in the specified file is activated.

Default Cases

If PathName is a zero-length string (""), GetObject returns a new object instance of the specified class type. If the PathName argument is omitted, GetObject returns a currently active object of the class type specified in Class. If no object of the specified type exists, an error occurs.

Accessing a Subobject

Some applications allow you to activate a subobject associated with a file. To do this, add an exclamation point (!) to the end of the file name and follow it with a string that identifies the part of the file you want to activate. For information on how to create this string, see the documentation for the application that created the object.

For example, in a drawing application you might have multiple layers to a drawing stored in a file. You could use the following code to activate a layer within a drawing called schema.cad.

layerObject = GetObject("C:\CAD\schema.cad!Layer3")

Specifying a Class

If you do not specify the object's Class, Automation determines the application to start and the object to activate, based on the file name you provide. Some files, however, can support more than one class of object. For example, a drawing might support three different types of objects: an Application object, a Drawing object, and a Toolbar object, all of which are part of the same file. To specify which object in a file you want to activate, use the optional Class argument. The following example illustrates this.

Dim drawObj As Object
drawObj = GetObject("C:\Drawings\sample.drw", "Figment.Drawing")

In the preceding example, Figment is the name of a drawing application and Drawing is one of the object types it supports.

Using the Object

Once an object is activated, you refer to it in code using the object variable you declared. In the preceding example, you access properties and methods of the new object using the object variable drawObj. The following example illustrates this.

drawObj.Line(9, 90)
drawObj.InsertText(9, 100, "Hello, world.")
drawObj.SaveAs("C:\Drawings\sample.drw")

Note

Use the GetObject function when there is a current instance of the object or if you want to create the object with a file loaded. If there is no current instance, and you do not want the object started with a file loaded, use the CreateObject Function (Visual Basic).

If an object has registered itself as an ActiveX single-instance object, only one instance of the object is created, no matter how many times CreateObject is called. With a single-instance object, GetObject always returns the same instance when called with the zero-length string ("") syntax, and it causes an error if the PathName argument is omitted. You cannot use GetObject to obtain a reference to a class created with Visual Basic.

Security Note:
The GetObject function requires unmanaged code permission, which might affect its execution in partial-trust situations. For more information, see SecurityPermission and Code Access Permissions.

When you are finished using the object, set all references to the object to Nothing. This allows the runtime to dispose of the COM component.

Example

The following example uses the GetObject function to determine whether Excel is running.

' Test to see if a copy of Excel is already running. 
Private Sub testExcelRunning()
    On Error Resume Next 
    ' GetObject called without the first argument returns a 
    ' reference to an instance of the application. If the 
    ' application is not already running, an error occurs. 
    Dim excelObj As Object = GetObject(, "Excel.Application")
    If Err.Number = 0 Then
        MsgBox("Excel is running")
    Else
        MsgBox("Excel is not running")
    End If
    Err.Clear()
    excelObj = Nothing 
End Sub

The following example uses the GetObject function to obtain a reference to a specific Microsoft Excel worksheet (excelObj). The call to GetObject returns a reference to the worksheet represented by the specified file, test.xls. Next, the example code makes both Excel and the window containing the specified worksheet visible.

This example requires Option Strict Off because it uses late binding, where objects are assigned to variables of type Object. You can specify Option Strict On and declare objects of specific object types if you add a project reference to the Excel type library. To do so, open the Add Reference dialog box from the Project menu in Visual Studio and select the Excel type library on the COM tab.

' Add Option Strict Off to the top of your program. 
Option Strict Off

Private Sub getExcel()
    Dim fileName As String = "c:\vb\test.xls" 

    If Not My.Computer.FileSystem.FileExists(fileName) Then
        MsgBox(fileName & " does not exist")
        Exit Sub 
    End If 

    ' Set the object variable to refer to the file you want to use. 
    Dim excelObj As Object = GetObject(fileName)
    ' Show Excel through its Application property. 
    excelObj.Application.Visible = True 
    ' Show the window containing the file. 
    Dim winCount As Integer = excelObj.Parent.Windows.Count()
    excelObj.Parent.Windows(winCount).Visible = True 

    ' Insert additional code to manipulate the test.xls file here. 
    ' ...

    excelObj = Nothing 
End Sub

Smart Device Developer Notes

This function is not supported.

Requirements

Namespace:Microsoft.VisualBasic

**Module:**Interaction

Assembly: Visual Basic Runtime Library (in Microsoft.VisualBasic.dll)

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