Call COM object method with optional parameters.

  • Thread starter Thread starter Yong Jiang
  • Start date Start date
Y

Yong Jiang

I am trying to convert some vb code calling COM oboject
methods to C#. Example shown as follows

Dim Stream As New ADODB.Stream
Call Stream.Open()

Stream.Open has three optional parameters. I am trying to
convert it to C# as shown as follows

ADODB.Stream Stream = null;
Stream = new ADODB.Stream();
Stream.Open();

Somehow, C# does not like leaving paramters blank. I don't
know how to get around of it. Any help will be
appreciated.
 
Yong,

C# does not support optional parameters, so you are going to have to
pass in a value of Missing for all of the parameters that you do not want to
pass in. In order to do that, you will want to do the following:

// Get a missing value.
object pobjMissing = System.Reflection.Missing.Value;

// Make the call.
ADODB.Stream pobjStream = new ADODB.Stream();
pobjStream.Open(pobjMissing, pobjMissing, pobjMissing, pobjMissing,
pobjMissing);

Hope this helps.
 
I appreciate your help.

Now I got the following error messages.

Argument '2': convert from 'object'
to 'ADODB.ConnectModeEnum'
Argument '3': convert from 'object'
to 'ADODB.StreamOpenOptionEnum
Argumetn '4': connot convert from 'object' to 'string'
Argumetn '5': connot convert from 'object' to 'string'

After I changed it to the following to make complier happy

Stream.Open(objMissing, (ADODB.ConnectModeEnum)
objMissing, (ADODB.StreamOpenOptionsEnum) objMissing,
(string) objMissing, (string) objMissing);

I got runtime errors: Specified cast is not valid.

Once again. Thank you for the help.
-----Original Message-----
Yong,

C# does not support optional parameters, so you are going to have to
pass in a value of Missing for all of the parameters that you do not want to
pass in. In order to do that, you will want to do the following:

// Get a missing value.
object pobjMissing = System.Reflection.Missing.Value;

// Make the call.
ADODB.Stream pobjStream = new ADODB.Stream();
pobjStream.Open(pobjMissing, pobjMissing, pobjMissing, pobjMissing,
pobjMissing);

Hope this helps.


--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)

Yong Jiang said:
I am trying to convert some vb code calling COM oboject
methods to C#. Example shown as follows

Dim Stream As New ADODB.Stream
Call Stream.Open()

Stream.Open has three optional parameters. I am trying to
convert it to C# as shown as follows

ADODB.Stream Stream = null;
Stream = new ADODB.Stream();
Stream.Open();

Somehow, C# does not like leaving paramters blank. I don't
know how to get around of it. Any help will be
appreciated.
Click to expand...


.
Click to expand...
 
These parameter are optional params but not variants. You will need to pass in an empty string (string.Empty i think) for params 4
and 5 and use the correct enum for 2 and 3. Only param 1 is a variant.

--
Michael Culley


Yong Jiang said:
I appreciate your help.

Now I got the following error messages.

Argument '2': convert from 'object'
to 'ADODB.ConnectModeEnum'
Argument '3': convert from 'object'
to 'ADODB.StreamOpenOptionEnum
Argumetn '4': connot convert from 'object' to 'string'
Argumetn '5': connot convert from 'object' to 'string'

After I changed it to the following to make complier happy

Stream.Open(objMissing, (ADODB.ConnectModeEnum)
objMissing, (ADODB.StreamOpenOptionsEnum) objMissing,
(string) objMissing, (string) objMissing);

I got runtime errors: Specified cast is not valid.

Once again. Thank you for the help.
-----Original Message-----
Yong,

C# does not support optional parameters, so you are going to have to
pass in a value of Missing for all of the parameters that you do not want to
pass in. In order to do that, you will want to do the following:

// Get a missing value.
object pobjMissing = System.Reflection.Missing.Value;

// Make the call.
ADODB.Stream pobjStream = new ADODB.Stream();
pobjStream.Open(pobjMissing, pobjMissing, pobjMissing, pobjMissing,
pobjMissing);

Hope this helps.


--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)

Yong Jiang said:
I am trying to convert some vb code calling COM oboject
methods to C#. Example shown as follows

Dim Stream As New ADODB.Stream
Call Stream.Open()

Stream.Open has three optional parameters. I am trying to
convert it to C# as shown as follows

ADODB.Stream Stream = null;
Stream = new ADODB.Stream();
Stream.Open();

Somehow, C# does not like leaving paramters blank. I don't
know how to get around of it. Any help will be
appreciated.
Click to expand...


.
Click to expand...
Click to expand...
 
After I used the following statement

Stream.Open(objMissing,
ADODB.ConnectModeEnum.adModeUnknown,
ADODB.StreamOpenOptionsEnum.adOpenStreamUnspecified,
string.Empty, string.Empty)

it seems to work fine. I can not use empty string for the
second parameter and third parameter.

Thank you for the help. It is very helpful. Have a very
nice thanks giving.

Yong
-----Original Message-----
These parameter are optional params but not variants. You
Click to expand...
will need to pass in an empty string (string.Empty i
think) for params 4
and 5 and use the correct enum for 2 and 3. Only param 1 is a variant.

--
Michael Culley


I appreciate your help.

Now I got the following error messages.

Argument '2': convert from 'object'
to 'ADODB.ConnectModeEnum'
Argument '3': convert from 'object'
to 'ADODB.StreamOpenOptionEnum
Argumetn '4': connot convert from 'object' to 'string'
Argumetn '5': connot convert from 'object' to 'string'

After I changed it to the following to make complier happy

Stream.Open(objMissing, (ADODB.ConnectModeEnum)
objMissing, (ADODB.StreamOpenOptionsEnum) objMissing,
(string) objMissing, (string) objMissing);

I got runtime errors: Specified cast is not valid.

Once again. Thank you for the help.
-----Original Message-----
Yong,

C# does not support optional parameters, so you are going to have to
pass in a value of Missing for all of the parameters
Click to expand...
that
you do not want to
pass in. In order to do that, you will want to do the following:

// Get a missing value.
object pobjMissing = System.Reflection.Missing.Value;

// Make the call.
ADODB.Stream pobjStream = new ADODB.Stream();
pobjStream.Open(pobjMissing, pobjMissing, pobjMissing, pobjMissing,
pobjMissing);

Hope this helps.


--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)

I am trying to convert some vb code calling COM oboject
methods to C#. Example shown as follows

Dim Stream As New ADODB.Stream
Call Stream.Open()

Stream.Open has three optional parameters. I am
Click to expand...
trying
to
convert it to C# as shown as follows

ADODB.Stream Stream = null;
Stream = new ADODB.Stream();
Stream.Open();

Somehow, C# does not like leaving paramters blank. I don't
know how to get around of it. Any help will be
appreciated.



.
Click to expand...
Click to expand...


.
Click to expand...
 
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