How to Build an EA that Trades Trendlines in Mql4

Here is a complete, fully functional MQL4 Expert Advisor (robot) designed to buy when the price breaks above a specific trendline.

How it works

1. Draw a Trendline: You draw a trendline on the chart manually.
2. Name the Trendline: You must name the trendline "BuyLine" (or whatever name you set in the inputs) in the object properties.
3. Logic: The robot monitors that specific line. If the price crosses from below the line to above the line, it executes a Buy order.

MQL4 Code

//+------------------------------------------------------------------+
//|                                        TrendlineBreakoutBuy.mq4  |
//|                                     Copyright 2023, Quantitative |
//|                                             https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright "Copyright 2023, Quantitative"
#property link      "https://www.mql5.com"
#property version   "1.00"
#property strict

//--- Input Parameters
input string InpTrendLineName = "BuyLine"; // Name of the trendline to monitor
input double InpLotSize       = 0.1;       // Trading volume
input int    InpStopLoss      = 50;        // Stop Loss in points (0 = none)
input int    InpTakeProfit    = 100;       // Take Profit in points (0 = none)
input int    InpMagicNumber   = 8899;      // Unique ID for this EA's trades
input int    InpSlippage      = 3;         // Max slippage in points

//--- Global Variables
datetime lastBarTime = 0;

//+------------------------------------------------------------------+
//| Expert initialization function                                   |
//+------------------------------------------------------------------+
int OnInit()
{
   // Check if the trendline exists on startup
   if(ObjectFind(0, InpTrendLineName) < 0)
   {
      Print("Warning: Trendline named '", InpTrendLineName, "' not found. Please draw it and rename it.");
   }
   
   return(INIT_SUCCEEDED);
}

//+------------------------------------------------------------------+
//| Expert deinitialization function                                 |
//+------------------------------------------------------------------+
void OnDeinit(const int reason)
{
   Comment(""); // Clear chart comments
}

//+------------------------------------------------------------------+
//| Expert tick function                                             |
//+------------------------------------------------------------------+
void OnTick()
{
   // 1. Check if the trendline exists
   if(ObjectFind(0, InpTrendLineName) < 0)
   {
      Comment("Waiting for trendline named: ", InpTrendLineName);
      return;
   }

   // 2. Check if we already have an open trade for this EA
   if(CountOpenTrades() > 0)
   {
      Comment("Trade active. Monitoring...");
      return;
   }

   // 3. Get Trendline Price values
   // Price at current bar (Shift 0)
   double linePriceCurrent = ObjectGetValueByShift(InpTrendLineName, 0);
   // Price at previous bar (Shift 1)
   double linePricePrevious = ObjectGetValueByShift(InpTrendLineName, 1);

   // 4. Check for Breakout Condition
   // Condition: Previous Close was BELOW the line, and Current Ask is ABOVE the line
   // This ensures we catch the crossover moment and don't buy if price is already way above.
   
   double prevClose = iClose(Symbol(), Period(), 1);
   double currentAsk = Ask;

   Comment("Line Price: ", DoubleToString(linePriceCurrent, Digits), "\nAsk Price: ", DoubleToString(currentAsk, Digits));

   if(prevClose < linePricePrevious && currentAsk > linePriceCurrent)
   {
      OpenBuyOrder();
   }
}

//+------------------------------------------------------------------+
//| Function to Open Buy Order                                       |
//+------------------------------------------------------------------+
void OpenBuyOrder()
{
   double sl = 0;
   double tp = 0;

   // Calculate Stop Loss
   if(InpStopLoss > 0)
      sl = NormalizeDouble(Ask - InpStopLoss * Point, Digits);

   // Calculate Take Profit
   if(InpTakeProfit > 0)
      tp = NormalizeDouble(Ask + InpTakeProfit * Point, Digits);

   // Send Order
   int ticket = OrderSend(Symbol(), OP_BUY, InpLotSize, Ask, InpSlippage, sl, tp, "TL Breakout", InpMagicNumber, 0, clrBlue);

   if(ticket < 0)
   {
      Print("OrderSend failed with error #", GetLastError());
   }
   else
   {
      Print("Buy Order Opened Successfully. Ticket: ", ticket);
      // Optional: Delete the line after trade to prevent re-entry
      // ObjectDelete(0, InpTrendLineName); 
   }
}

//+------------------------------------------------------------------+
//| Helper: Count open trades for this EA                            |
//+------------------------------------------------------------------+
int CountOpenTrades()
{
   int count = 0;
   for(int i = OrdersTotal() - 1; i >= 0; i--)
   {
      if(OrderSelect(i, SELECT_BY_POS, MODE_TRADES))
      {
         if(OrderSymbol() == Symbol() && OrderMagicNumber() == InpMagicNumber && OrderType() == OP_BUY)
         {
            count++;
         }
      }
   }
   return count;
}
//+------------------------------------------------------------------+

How to Setup and Use

1. Install the Code:

   • Open MetaTrader 4.
   • Press F4 to open the MetaEditor.
   • Click New -> Expert Advisor (template) -> Name it "TrendlineBreakout".
   • Paste the code above into the file, replacing everything else.
   • Press F7 to Compile.

2. Prepare the Chart:

   • Go back to the main MT4 window.
   • Draw a Trendline on the chart where you want the breakout to occur.
   • Crucial Step: Double-click the trendline to select it, right-click, go to Properties -> Common tab. Change the Name field to BuyLine.

3. Activate the Robot:

   • Drag the "TrendlineBreakout" EA from the Navigator onto the chart.
   • Ensure "Allow live trading" is checked in the Common tab.
   • Ensure the "AutoTrading" button at the top of MT4 is Green.

Strategy Logic Explained

• Object Detection: The code uses ObjectGetValueByShift to mathematically calculate the price of the trendline at the current moment (Shift 0) and the previous candle (Shift 1).
• Crossover Check: It checks if the Previous Candle Close was below the trendline AND the Current Ask Price is above the trendline. This confirms a fresh breakout.
• Trade Management: It calculates Stop Loss and Take Profit based on points and sends the order. It also checks CountOpenTrades to ensure it doesn't open multiple trades on the same breakout tick.

Q&A

Q: Can I use a different name for the trendline?
A: Yes. In the Expert Advisor inputs tab when you attach it to the chart, change InpTrendLineName to whatever you prefer.

Q: Will this work for Sell trades?
A: This specific code is hardcoded for Buy trades only. To make it sell, the logic needs to be reversed (Previous Close > Line AND Bid < Line).

Q: What happens if the price is already above the line when I turn the robot on?
A: The robot will not trade. It specifically looks for the moment of the cross (Previous bar below, current price above). This prevents buying at a bad price if you restart the terminal.

Q: Does the trendline need to be extended to the right?
A: No. The function ObjectGetValueByShift calculates the mathematical trajectory of the line infinitely. However, visually extending it (Ray) helps you see where the price needs to go.