Interactions between Expert Advisor and Indicators

Is it possible to read changes in pre-built indicator (for example: its value changes) through an expert-advisor, and of course - automate the trades based on those reads?

What is the function that is responsible for doing this?

I have tried to look this up on Google, but it appears I can only do things like track object creation or deletion ... called Chart Events.... maybe I'm missing something?

回答1:

Yes, it is possible.

MetaTrader4 Terminal is a software platform, that allows you to launch

1x soloist Expert Advisor - as an event-driven code-execution algorith per each MT4.Graph
Nx concurrent Custom Indicator-s event-driven restricted code-base per each MT4.Graph
1x soloist Script asynchronous code-execution unit per each MT4.Graph

This inventory is important, as you have no other means how to automate complex Trading Algorithmisation but this.

Technical Indicators are executed under one common thread, which poses limitations for real-time robustness plus some restrictions apply for the permitted / forbidden operations that might be coded / compiled / executed in Indicator ( all aim at avoiding any and all possible blocking situations ( ref. solo-thread for all ... ) )

This said, you might have noticed, that both Expert Advisor and Technical Indicator-s are externally synchronised ( forget for the moment about non-parallel, shared thread execution with principal nanosecond scale of asynchronicity due to resource / code-execution scheduling ) and bound to externally issued anFxMarketEVENT in a form of an arriving signal ( once a price moves, MT4.Server sends QUOTE downstream message to the MT4.Terminal, a.k.a. a Tick ), which once ( if ) received, triggers MQL4 code-execution facilities on localhost:

OnTick(){ ...} # in case of Expert Advisor
OnCalculate(){...} # in case of Custom Technical Indicator

What is the function that is responsible for this?

Directly? None.

Indirectly? The one you construct and make responsible for registering / monitoring the changes of such value ( be it internally in MQL4 domain or externally via distributed processing model, incl. GPU-cluster one for more demanding processing, where internal shared-thread execution fails to meet the timing constraints ):

bool hasAnIndicatorChanged( double aTol = 0.00001 ){    // DERIVATION
     static double prevVALUE = EMPTY_VALUE;             // .DEF
            double aNewVALUE = iBWMFI( _Symbol,         //      .SYM
                                       PERIOD_CURRENT,  //      .PERIOD
                                       0                //      .HOT[0]
                                       );               // .STO "current"
     if (  MathAbs( aNewVALUE - prevVALUE ) <= aTol ){
           prevVALUE = aNewVALUE;
           return( False ); // JIT/RET --> --> --> --> --> non-MISRA-C JIT/RET
     }
     else {
           prevVALUE = aNewVALUE;
           return( True );  // JIT/RET --> --> --> --> --> non-MISRA-C JIT/RET
     }
}

Can do principle

One may create a similarly trivial or a bit more complex PID-monitor and ask from Expert Advisor each time an OnTick() is being called ( thus align the code execution with the internal event-handler at no additional cost ).

void OnTick(){
     if (  hasAnIndicatorChanged() ){
           ... 
     }
     ...
}

回答2:

Ok I found it.

In order to use a custom indicator as a tool for a buy / trade decision inside an expert advisor, the function is iCustom()