Error: "No parameterless constructor defined for this object."

  • Thread starter Thread starter Sachi
  • Start date Start date
S

Sachi

Hi,
I am trying to invoke as like below.

Form frmChild = (Form) Activator.CreateInstance
(typeInstance);
frmChild.MdiParent =
_parentForm;
frmChild.StartPosition =
FormStartPosition.CenterScreen;
frmChild.Show();

When I invoke a form it works fine after frmchild is
shown it is giving error saying "No parameterless
constructor defined for this object.". But still works.

Catch is when i again invoke some child frm from
frmChild it throws again "No parameterless constructor
defined for this object." and fails to load any form.

But when i remove mdiparent property it works fine.
That is not the soultion i want. I want all the forms
inside MDI application.

There is no clue or solution soo far. Hope someone can
share some light on this problem.

Best Regards,
Sachi
 
Sachi said:
I am trying to invoke as like below.

Form frmChild = (Form) Activator.CreateInstance
(typeInstance);
frmChild.MdiParent =
_parentForm;
frmChild.StartPosition =
FormStartPosition.CenterScreen;
frmChild.Show();

When I invoke a form it works fine after frmchild is
shown it is giving error saying "No parameterless
constructor defined for this object.". But still works.
Click to expand...

What do you mean by "but still works"? It won't have created the form.

Basically, Activator.CreateInstance tries to invoke a parameterless
constructor. If there isn't one, it can't create an instance.
Catch is when i again invoke some child frm from
frmChild it throws again "No parameterless constructor
defined for this object." and fails to load any form.
Click to expand...

With the above, frmChild will never actually be assigned to, so you'll
need to clarify exactly what you're doing.
 
What do you mean by "but still works"? It won't have
created the form.
Click to expand...
Well, When I remove this line

frmChild.MdiParent = _parentForm;

it works as a modelform and which is not part of MDI
application. But I want all the forms to be part of MDI.

I checked out all the forms which i am invoking. There
is constructor and there is no parameters for those
constructors.

Hope to solve it soon. :) .

Thanks and Regards,
Sachi
 
sachi said:
Well, When I remove this line

frmChild.MdiParent = _parentForm;

it works as a modelform and which is not part of MDI
application. But I want all the forms to be part of MDI.
Click to expand...

It won't even *get* to that line though, if Activator.CreateInstance
has thrown an exception.
I checked out all the forms which i am invoking. There
is constructor and there is no parameters for those
constructors.

Hope to solve it soon. :) .
Click to expand...

At this stage we really need a complete example, because I can't see
how the various things you're saying tie in with each other.

See http://www.pobox.com/~skeet/csharp/complete.html
 
Sachi said:
Can I discuss this offline so then i can post details on
code?
Click to expand...

Of course. If your example could be as simple as possible (while still
demonstrating the problem) that would help a lot.
 
* "Sachi said:
Hi,
I am trying to invoke as like below.

Form frmChild = (Form) Activator.CreateInstance
(typeInstance);
frmChild.MdiParent =
_parentForm;
frmChild.StartPosition =
FormStartPosition.CenterScreen;
frmChild.Show();

When I invoke a form it works fine after frmchild is
shown it is giving error saying "No parameterless
constructor defined for this object.". But still works.
Click to expand...

Which line throws the exception?
 
frmChild = (Form) Activator.CreateInstance(typeInstance);
frmChild.MdiParent = _parentForm;
frmChild.StartPosition = FormStartPosition.CenterScreen;
frmChild.Show();


In the above code when i am trying to assign mdiparent
only it is throwing error.

It is highly clubbed with lot of forms. I will send you a
sample to your mail id more similar example.

...
Sachi
 
protected virtual void OnMenuItemClick(object sender,
EventArgs e)
{

DynamicMenuItem menuItem = (DynamicMenuItem)sender;
if(menuItem.Expression == "") return;

// The first object we need is a reflection of the
// current object, encapsulated in a "Type" object.
Type thisType = this.GetType();

// Now we look for the method in question, using the
// Type.GetMethod(string) method, which will return a
// MethodInfo representation object, or null if no matching
// method was found

MethodInfo theMethod = thisType.GetMethod
(menuItem.Expression);
theMethod.Invoke(this, userParameters);

}

Above code I am using to invoke method dynamically when
clicked on the menuitem.

Also I am overloading in the base form onLoad method too.

Any clue?

Best Regards,
Sachi
 
* "Sachi said:
frmChild.MdiParent = _parentForm;

Above line throws the error.
Click to expand...

I don't understand that. There is no ctor called in this line. Did you
place 'Try...Catch' around this line?
 
Sachi said:
frmChild.MdiParent = _parentForm;

Above line throws the error.
Click to expand...

Are you absolutely sure? That seems a very odd line to get the error
on, but the Activator.CreateInstance line would be a very *normal*
place to get the error.

Are you able to step over the Activator.CreateInstance line in the
debugger, for example?
 
Ya, I am very much sure about this line.
It throws error when trying to set mdiparent for frmChild
form.

CreateInstance works perfectly. I had been debugging on
this for more then 5hours :( .
Because it is been throwing error this line i am now with
no clue to guess.

Only thing i thought was something related to base class
constructor. But when i run in debugg mode - all the
constructor is called without any any exception thrown.

...
Sachi
 
Back
Top