如何从MQL4 / MQL5中的iADX（）指标中提取+ DI和-DI值？

Question

I'm a noob at MQL4 and I am writing my first EA.

My goal is to get the variables of the +DI and -DI of the ADX Indicator.
I used the iADX() function as shown here:

double a;

int OnInit() {

    a = iADX( NULL, 0, 0, PRICE_CLOSE, MODE_PLUSDI, 0 );

    Alert( a );
}

But it keeps printing 0.0

Did I enter the parameters wrong on the iADX() function?

I'd just like to pull the values of +DI and -DI so I can use them in my code.

Answer 1

Syntax first:

double iADX( string symbol,        // BEST AS: _Symbol
             int    timeframe,     // BEST AS: one of {}-ENUMs ~ PERIOD_CURRENT
             int    period,        //          averaging period 
             int    applied_price, // BEST AS: one of {}-ENUMs ~ PRICE_CLOSE
             int    mode,          // BEST AS: one of {}-ENUMs ~ MODE_PLUSDI
             int    shift          //          shift 
             );

---

Why 0.0 ?

Once we read into the calling interface, requirement to average the selected sequence of PRICE_CLOSE records, kept for the current Symbol() ( NULL ) seems fair, but just notice, that doing that for zero-consecutive bars instructs to do nothing, instead of taking some reasonable calculus of SUM( Close[i..j] )/period to allow for any meaningful processing.

Experiment with non-zero periods and you are back on the rails, aiming towards your goals.

double DI_plus,
       DI_minus;
int    ADX_PERIOD = 8;

int    OnInit() {
       ObjectCreate( ChartID(), "GUI-SHOW+DI", ... );               // LABEL for +DI
       ObjectCreate( ChartID(), "GUI-SHOW-DI", ... );               // LABEL for -DI
       }

int    OnTick() {

       DI_plus  = iADX( _Symbol,
                        PERIOD_CURRENT,
                        ADX_PERIOD,
                        PRICE_CLOSE,
                        MODE_PLUSDI,
                        0
                        );
       DI_minus = iADX( _Symbol,
                        PERIOD_CURRENT,
                        ADX_PERIOD,
                        PRICE_CLOSE,
                        MODE_MINUSDI,
                        0
                        );
       ObjectSetString( Chart_ID(),
                        "GUI-SHOW+DI",
                        OBJPROP_TEXT,
                        StringFormat("+DI %12.6f", DI_plus )
                        );
       ObjectSetString( Chart_ID(),
                        "GUI-SHOW-DI",
                        OBJPROP_TEXT,
                        StringFormat("-DI %12.6f", DI_minus )
                        );
       }

Answer 2

ADX has one parameter - its period. and you use indicator with period = 0, in such case it returns zeros...

double a;
int period = 14;

int OnInit() {
   a = iADX( NULL, 0, period, PRICE_CLOSE, MODE_PLUSDI, 0 );
   Alert( a );
}

Also I am not sure it is a good idea to call indicator in OnInit() - sometimes you do not have bars already loaded and sometimes you have, maybe it is fixed but I remember several months ago my client had such problem especially when changing timeframes.