EMA in NinjaTrader — NinjaScript (C#) Source

The EMA in NinjaScript is barely longer than the SMA — a single recurrence in OnBarUpdate — but it introduces the pattern of referencing your own prior output, which you’ll use constantly. See the explainer for the concept.

What you’ll need

• NinjaTrader 8
• New → NinjaScript Editor → Indicators → New Indicator, name it AlgoGenEMA

The source

#region Using declarations
using System;
using System.Windows.Media;
using NinjaTrader.NinjaScript;
using NinjaTrader.NinjaScript.Indicators;
#endregion

namespace NinjaTrader.NinjaScript.Indicators
{
    public class AlgoGenEMA : Indicator
    {
        private double alpha;
        private double runningSum;

        protected override void OnStateChange()
        {
            if (State == State.SetDefaults)
            {
                Name        = "AlgoGen EMA";
                Description = "Exponential Moving Average";
                Period      = 20;
                IsOverlay   = true;

                AddPlot(new Stroke(Brushes.OrangeRed, 2), PlotStyle.Line, "EMA");
            }
            else if (State == State.Configure)
            {
                alpha = 2.0 / (Period + 1.0);
                runningSum = 0;
            }
        }

        protected override void OnBarUpdate()
        {
            if (CurrentBar < Period - 1)
            {
                // Accumulate the SMA seed over the first window.
                runningSum += Close[0];
                if (CurrentBar == Period - 2)
                    return;                       // still filling the seed window
            }

            if (CurrentBar == Period - 1)
            {
                runningSum += Close[0];
                Value[0] = runningSum / Period;   // seed with SMA of first window
            }
            else if (CurrentBar >= Period)
            {
                Value[0] = alpha * Close[0] + (1 - alpha) * Value[1];
            }
        }

        #region Properties
        [NinjaScriptProperty]
        [System.ComponentModel.DataAnnotations.Range(1, int.MaxValue)]
        [System.ComponentModel.Display(Name = "Period", GroupName = "Parameters", Order = 0)]
        public int Period { get; set; }
        #endregion
    }
}

Compile & apply

1. Press F5 to compile.
2. Add AlgoGen EMA to a chart, set the period. Because IsOverlay = true, it draws on price, matching the orange EMA in the output chart.

Gotchas

• Seed then recurse. We accumulate an SMA over the first Period bars to seed Value[0], then switch to the α·Close + (1−α)·Value[1] recurrence. This matches NinjaTrader’s built-in EMA convention.
• Value[1] is the prior EMA. Referencing your own previous plotted value is the idiom that makes recursive indicators work in NinjaScript.
• Built-in shortcut. EMA(Close, Period)[0] exists; rolling your own is for learning and full control.
• State.Configure for alpha. Computing alpha once in Configure (rather than every bar in OnBarUpdate) is a small efficiency habit worth forming — it only depends on Period, which can’t change mid-run.
• Don’t reset Value on reload. Because the recurrence reads Value[1], NinjaTrader’s historical processing rebuilds it correctly bar by bar; you don’t need to persist anything yourself beyond the plotted series.

That’s the five-language set: Python, MQL5, Pine Script, EasyLanguage, and this one. Now compare EMA vs SMA on real data in AlgoGen.

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This post is educational, not financial advice. Indicators describe the past; they don’t predict the future. Backtest anything before you risk real money on it.