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Question

I know this is a basic coding question but I am learning on the job and trying to figure out the parameter this method is looking for, because when I leave it blank it seems to tell me it is looking for "position", which is what I have in there. This is referring to the OnTradeCalledBack and OnPositionCalledBack methods.

This is the error I get when leaving the parameter blank:

There is no argument given that corresponds to the required formal parameter 'position' of 'SocketServer.AsynchronousSocketListener.MyPositionCallBackEventHandler' SocketServer

Here is the code:

public class AsynchronousSocketListener
{
    public AsynchronousSocketListener(int port)
    {
    }

    //Need to create a delagate to handle the positions and trade information.
    public delegate void MyPositionCallBackEventHandler(TposPositionCallback position);
    public delegate void MyTradeCallBackEventHandler(TposTradeCallback trade);

    //Indicates something has happened and finished.
    //Event defined here, based on delegate

    public event MyPositionCallBackEventHandler PositionCalledBack;
    public event MyTradeCallBackEventHandler TradeCalledBack;

    //Raise the Event, need a method to do this.
    //Responsible for notifying subscribers

    protected virtual void OnPositionCalledBack()
    {
        //need to fix this, just added local to avoid error
        //TposPositionCallback position = null;
        if (PositionCalledBack != null)
            PositionCalledBack(position);
    }

    protected virtual void OnTradeCalledBack()
    {
        //need to fix this, just added local to avoid error
        //TposTradeCallback trade = null;
        if (TradeCalledBack != null)
            TradeCalledBack();
    }
}

Answer 1

Looking into the code TradeCalledBack is an event with a signature of:

public event MyTradeCallBackEventHandler TradeCalledBack;

Therefore TradeCalledBack will need to have the parameters passed to it that are defined in the MyTradeCallBackEventHandler which is a delegate with a signature of:

public delegate void MyTradeCallBackEventHandler(TposTradeCallback trade);

Therefore TradeCalledBack needs to have a variable of type TposTradeCallback passed into it.

To overcome the error you can pass null into the method as such:

TradeCalledBack(null);

or change the whole method to something like the following and pass the variable into it:

protected virtual void OnTradeCalledBack(TposTradeCallback trade)
{
    if (TradeCalledBack != null)
    {
        TradeCalledBack(trade);
    }
}

Following the logic here you can do similar changes for OnPositionCalledBack .

Answer 2

just change the definition to

public delegate void MyPositionCallBackEventHandler(TposPositionCallback position = null);

which passes null as default if no parameter is supplied