Strategy-partly-based-upon-price-movement-of-another-symbol

it’s also possible in Building Blocks via the External Symbol Qualifier.

That's amazing. Thanks very much.

I am not sure if the code is correct. When I add some simple buy and sell conditions, I get "Object reference not set to an instance of an object" at the code line:

if (_spy.Close[idx] > _smaSpy[idx])

CODE:
  using WealthLab.Backtest;
using System;
using WealthLab.Core;
using WealthLab.Indicators;
using WealthLab.ChartWPF;
using System.Drawing;
using System.Collections.Generic;

namespace WealthScript1
{
   public class MyStrategya : UserStrategyBase
   {
      //plot some market benchmarks along with the symbol being charted
      public override void Initialize(BarHistory bars)
      {
         BarHistory _spy = GetHistory(bars, "SPY");
         PlotBarHistory(_spy, "SPYPane", Color.Silver);
         _smaSpy = SMA.Series(_spy.Close, 50);
         PlotIndicator(_smaSpy, default, default, default, "SPYPane");

         //new
         indicator1 = new EMA(bars.Close, 2);
         PlotIndicator(indicator1, Color.FromArgb(255, 0, 0, 0));
         indicator2 = new EMA(bars.Close, 5);
         PlotIndicator(indicator2, Color.FromArgb(255, 0, 0, 255));
         
            StartIndex = 5;

      }

      public override void Execute(BarHistory bars, int idx)
      {
         if (!HasOpenPosition(bars, PositionType.Long))
         {
            if (_spy.Close[idx] > _smaSpy[idx])
            {
               //code your buy conditions here
               int index = idx;
               Position foundPosition0 = FindOpenPosition(0);
               bool condition0;
               if (foundPosition0 == null)
               {
                  condition0 = false;
                  {
                     if (indicator1.CrossesOver(indicator2, index))
                     {
                        condition0 = true;
                     }
                  }
                  if (condition0)
                  {
                     _transaction = PlaceTrade(bars, TransactionType.Buy, OrderType.Market, 0, 0, "Buy At Market (1)");
                  }
               }
               
               
               
            }
         }
         else
         {
            //code your sell conditions here

            _transaction = PlaceTrade(bars, TransactionType.Sell, OrderType.Market, 0, 0, "Sell At Market (1)");




            //         condition0 = false;
            //         {
            //            if (indicator12.CrossesUnder(indicator22, index))
            //            {
            //               condition0 = true;
            //            }
            //         }
            //         if (condition0)
            //         {
            //            ClosePosition(foundPosition0, OrderType.Market, 0, "Sell At Market (1)");
            //         }

         }
      }

      BarHistory _spy;
      SMA _smaSpy;

      private IndicatorBase indicator1;
      private IndicatorBase indicator2;

      private IndicatorBase indicator12;
      private IndicatorBase indicator22;
      
         private Transaction _transaction;
      
      
   }
}

You declare a variable _spy in the private variables section at the bottom, good. But then you declare the same variable again in Initialize. So, by the time Execute comes around, the original _spy is still unassigned and thus null.

You need to change

BarHistory _spy =

in Initialize to simply

_spy =

to use the same variable you declare in the private variables area.

Sorry, that was my mistake for not running the code after creating it! (Corrected my example above.)

QUOTE:
You declare a variable _spy in the private variables section at the bottom, good. But then you declare the same variable again in Initialize.

In other words, you declared two independent _spy variables, which is not what you want. You want one declaration that shares this variable between methods (Initialize and Execute).

Check your C# textbook for scoping rules with declarations for details so you get the big picture. But declare _spy once as a private variable outside the MyStrategy method blocks (such as Initialize), then just use that variable without including a BarHistory datatype declaration in the assignment within Initialize.

This is easy to understand, but only if you study the scoping rules in your C# textbook. The bits and pieces discussed in the forum won't explain why C# is designed this way, but the textbook will.

I just tried your corrected code, but still get the error at line 35:

if (_spy.Close[idx] > _smaSpy[idx]) Object reference not set to an instance of an object.

At least one error in your code is setting StartIndex = 5 when the SMA period is 50.

You problem is line 16. You are declaring a new copy of the _spy variable instead of using the one you declared at the bottom of the strategy.

Change

BarHistory _spy = GetHistory(bars, "SPY");

to

_spy = GetHistory(bars, "SPY");

Thanks Glitch. Works fine now.