Question

I have a backgroundworker in a C++ .NET forms application which runs async. In the DoWork function of this backgroundworker I want to add rows to a datagridview, however I can’t really figure out how to do this with BeginInvoke as the code I have doesn’t seem to work.

The code I have

delegate void invokeDelegate(array<String^>^row);

....
In the DoWork of the backgroundworker
....

array<String^>^row = gcnew array<String^>{"Test", "Test", "Test"};
if(ovlgrid->InvokeRequired)
    ovlgrid->BeginInvoke(gcnew invokeDelegate( this, &Form1::AddRow), row);

....

void AddRow(array<String^>^row)
{
 ovlgrid->Rows->Add( row );
}

The error I get is:

An unhandled exception of type
‘System.Reflection.TargetParameterCountException’ occurred in
mscorlib.dll

Additional information: Parameter count mismatch.

When I change to code to not pass any parameters it just works, the code than becomes:

delegate void invokeDelegate();

...
In the DoWork function
...

if(ovlgrid->InvokeRequired)
     ovlgrid->BeginInvoke(gcnew invokeDelegate( this, &Form1::AddRow));

...
void AddRow()
{
     array<String^>^row = gcnew array<String^>{"test","test2","test3"};
     ovlgrid->Rows->Add( row );
}

The problem though is that I want to pass parameters.
I was wondering what I’m doing wrong which causes the parametercountexception and how to fix this?

Answer 1

The problem you’ve run into is BeginInvoke takes an array of parameters and you pass it an array which happens to be the one parameter.

Parameters

method

Type: System.Delegate

The delegate to a method that takes parameters specified in args, which is pushed onto the Dispatcher event queue.

args

Type: System.Object[]

An array of objects to pass as arguments to the given method. Can be null.

Therefore, BeginInvoke takes this to mean you have 3 string parameters to the method: "test", "test2", and "test3". You need to pass an array containing just your row:

array<Object^>^ parms = gcnew array<Object^> { row };
ovlgrid.BeginInvoke(gcnew invokeDelegate(this, &Form1::AddRow), parms);