Getting a private variable through Reflection?

[David Veeneman]

I need to get a parent's private variable from within a control. Here's what
I'm doing: I have a control that I want to be able to detect the presence of
a particular (System.Compone ntModel) component on the same form. Components
aren't contained in the Form.Controls collection--they are contained in a
private Designer variable called 'components'. So, to detect the component,
I'm going to need to get to that private variable from the control's parent
form.

Does anyone have any sample code to get a private variable from a parent?
I'm new to Reflection, and I'm struggling a bit to sort it out. Thanks.

--
David Veeneman
Foresight Systems

[Marina Levit [MVP]]

Yes, the way it declares 'components' as a local variable is a major pain. I
have no idea why this was done - it makes inheritance a big pain when you
want the base class to do something with the components.

I don't know of a way to get the private variable using reflection.

What I had to do, was define an overridable property, and then the developer
of the inherited class has to override it, and return 'components'. That
way the base class can call the property, and polymorphically , the overriden
version will get called, thus getting the components.

"David Veeneman" <da****@nospam. com (domain is my last name)wrote in
message news:%2******** ********@TK2MSF TNGP03.phx.gbl. ..

>I need to get a parent's private variable from within a control. Here's
what I'm doing: I have a control that I want to be able to detect the
presence of a particular (System.Compone ntModel) component on the same
form. Components aren't contained in the Form.Controls collection--they are
contained in a private Designer variable called 'components'. So, to detect
the component, I'm going to need to get to that private variable from the
control's parent form.

Does anyone have any sample code to get a private variable from a parent?
I'm new to Reflection, and I'm struggling a bit to sort it out. Thanks.

--
David Veeneman
Foresight Systems

[Alan Pretre]

"David Veeneman" <da****@nospam. com (domain is my last name)wrote in
message news:%2******** ********@TK2MSF TNGP03.phx.gbl. ..

>I need to get a parent's private variable from within a control.

You use GetField().

http://msdn.microsoft.com/library/de...fieldtopic.asp

-- Alan

[David Veeneman]

get a parent's private variable from within a control.

>
You use GetField().

Thanks, Alan-- Here's what I've got.

Type parentForm = this.Parent.Get Type();
FieldInfo fieldInfo = parentForm.GetF ield("component s",
BindingFlags.In stance |
BindingFlags.No nPublic);
object fieldData = fieldInfo.GetVa lue(components) ;

The GetField() works, but the GetValue() fails. Here's the error I get:

Field 'components' defined on type 'MyApp.FormMain 1' is not a field on the
target object which is of type 'System.Compone ntModel.Contain er'.

Any idea what I'm missing? Thanks again.

--
David Veeneman
Foresight Systems

[Alan Pretre]

"David Veeneman" <da****@nospam. com (domain is my last name)wrote in
message news:%2******** ********@TK2MSF TNGP06.phx.gbl. ..

object fieldData = fieldInfo.GetVa lue(components) ;

Try

object fieldData = fieldInfo.GetVa lue(this.Parent );

-- Alan

[David Veeneman]

That did it! Thanks agsin.

--
David Veeneman
Foresight Systems

[Marina Levit [MVP]]

This is pretty cool, I learned something new.

"Alan Pretre" <no@spamwrote in message
news:er******** ******@TK2MSFTN GP06.phx.gbl...

"David Veeneman" <da****@nospam. com (domain is my last name)wrote in
message news:%2******** ********@TK2MSF TNGP06.phx.gbl. ..

>object fieldData = fieldInfo.GetVa lue(components) ;

Try

object fieldData = fieldInfo.GetVa lue(this.Parent );

-- Alan

[David Veeneman]

Here's the code for a control to iterate through the System.Componen tModel
components of its parent:

// Get the parent's components collection
Type parentForm = this.Parent.Get Type();
FieldInfo fieldInfo = parentForm.GetF ield("component s",
BindingFlags.In stance |
BindingFlags.No nPublic);
IContainer parent = (IContainer)fie ldInfo.GetValue (this.Parent);

// Check for a helper component
foreach (Component component in parent.Componen ts)
{
if (component.GetT ype() == typeof(MyHelper Component))
{
m_Helper = (MyHelperCompon ent)component;
}
}

Thanks again to Alan Pretre for his help.

--
David Veeneman
Foresight Systems

[David Veeneman]

>

I don't know of a way to get the private variable using reflection.

Actually, it can be done! See later messages in this thread.

--
David Veeneman
Foresight Systems

[Alan Pretre]

"David Veeneman" <da****@nospam. com (domain is my last name)wrote in
message news:OC******** ******@TK2MSFTN GP06.phx.gbl...

Here's the code for a control to iterate through the System.Componen tModel
components of its parent:

Note that in general it is unsafe to access private members of a class due
to the fact that future changes might be made to the thing you're prying
into. I got bit by this once with the switch from the .NET framework 1.x to
2.0. Was prying into something, which then disappeared in the later
release.

-- Alan