Hello everyone!

The default quantity of my strategy is "1" but, in certain condition, i would change this value in "2".
What follows is the code I am actually using:

 

Code

protected override void OnBarUpdate() { // Change the order quantity value when the profit factor drow down a certain level if (Performance.AllTrades.TradesPerformance.ProfitFactor < profit_factor_limit) { DefaultQuantity = 2; } }

The matter is that it changes the default quantity of all trades and not only the one which respects the condition set...

Does anyone know why?

In your case you don't change the DefaultQuantity. Instead you simply ask for quantity in the EnterLong() or short or any other Order Method.
As in:

 

Code

EnterLong(2)

Use the official help guide for reference:
NinjaTrader Version 7