Immediately after the client terminal loads a program (an Expert Advisor or custom indicator) and starts the process of initialization of global variables, the Init event will be sent, which will be processed by OnInit() event handler, if there is such. This event is also generated after a financial instrument and/or chart timeframe is changed, after a program is recompiled in MetaEditor, after input parameters are changed from the setup window of an Expert Advisor or a custom indicator. An Expert Advisor is also initialized after the account is changed. The Init event is not generated for scripts.
Before global variables are deinitialized and the program (Expert Advisor or custom indicator) is unloaded, the client terminal sends the Deinit event to the program. Deinit is also generated when the client terminal is closed, when a chart is closed, right before the security and/or timeframe is changed, at a successful program re-compilation, when input parameters are changed, and when account is changed.
The deinitialization reason can be obtained from the parameter, passed to the OnDeinit() function. The OnDeinit() function run is restricted to 2.5 seconds. If during this time the function hasn't been completed, then it is forcibly terminated. The Deinit event is not generated for scripts.
The Start event is a special event for script activation after it is loaded. This event is processed by OnStart handler. The Start event is not sent to Expert Advisors or custom indicators.
The NewTick event is generated if there are new quotes, it is processed by OnTick() of Expert Advisors attached. In case when OnTick function for the previous quote is being processed when a new quote is received, the new quote will be ignored by an Expert Advisor, because the corresponding event will not enqueued.
All new quotes that are received while the program is running are ignored until the OnTick() is completed. After that the function will run only after a new quote is received. The NewTick event is generated irrespective of whether automated trade is allowed or not ("Allow/prohibit Auto trading" button). The prohibition of automated trading denotes only that sending of trade requests from an Expert Advisor is not allowed, while the Expert Advisor keeps working.
The prohibition of automated trading by pressing the appropriate button will not stop the current execution of the OnTick() function.
The Calculate event is generated only for indicators right after the Init event is sent and at any change of price data. It is processed by the OnCalculate function.
The Timer event is periodically generated by the client terminal for the Expert Advisor that has activated the timer by the EventSetTimer function. Usually, this function is called by OnInit. Timer event processing is performed by the OnTimer function. After the operation of the Expert Advisor is completed, it is necessary to destroy the timer using the EventKillTimer function, which is usually called in the OnDeinit function.
The Trade event is generated when a trade operation is completed on a trade server. The Trade event is handled by the OnTrade() function for the following trade operations:
When performing some definite actions on a trade account, its state changes. Such actions include:
The following trade transactions are performed as a result of these actions:
For example, when sending a market buy order, it is handled, an appropriate buy order is created for the account, the order is then executed and removed from the list of the open ones, then it is added to the orders history, an appropriate deal is added to the history and a new position is created. All these actions are trade transactions. Arrival of such a transaction at the terminal is a TradeTransaction event. This event is handled by OnTradeTransaction function.
The Tester event is generated after testing of an Expert Advisor on history data is over. The event is handled by the OnTester() function.
The TesterInit event is generated with the start of optimization in the strategy tester before the first optimization pass. The TesterInit event is handled by the OnTesterInit() function.
The TesterDeinit event is generated after the end of optimization of an Expert Advisor in the strategy tester. The TesterDeinit event is handled by the OnTesterDeinit() function.
The ChartEvent event is generated by the client terminal when a user is working with a chart:
The BookEvent event is generated by the client terminal after the Depth Of Market is changed; it is processed by the OnBookEvent function. To start generation of BookEvent for the specified symbol, it is necessary to subscribe the symbol to this event by using the MarketBookAdd function.
To unsubscribe from BookEvent for a specified symbol, it is necessary to call the MarketBookRelease function. The BookEvent event is a broadcasting-type event - it means that it is sufficient to subscribe just one Expert Advisor for this event, and all other Expert Advisors that have the OnBookEvent event handler, will receive it. That's why it is necessary to analyze the symbol name, which is passed to a handler as a parameter.