Get selected records on the grid / datasource

This should also be a common task for Dynamics AX developers.
Fortunately, there's a little helper class in AX to make it easier for us, the MultiSelectionHelper.
For example, if you want to get a set of selected records in a grid, you could use it like this:

MyTableBuffer              myTableBuffer;
MultiSelectionHelper      selectionHelper   = MultiSelectionHelper::construct();
Set                             selectedRecords  = new Set(Types::Record);

selectionHelper.parmDataSource(myTableBuffer_DS);

myTableBuffer = selectionHelper.getFirst();

while (myTableBuffer)
{
    selectedRecords.add(myTableBuffer);
     myTableBuffer = selectionHelper.getNext();
} 

The code above should be very useful when getting the list of selected records directly on the form.
Another simplest way is
dataset.Columnname;
Eg.:
     MainAccount_ds is a dataset then  write like MainAccount.MainAccountId;
to get current selected row on the grid's Account Number.

if you want to get the selected records in a class that was called from a form, for example, you could use the MultiSelectionHelper like this:

public static void main(Args _args)

{   

    FormDataSource          formDataSource;   

    MyTableBuffer           myTableBuffer;

    FormRun                 caller = _args.caller();

    MultiSelectionHelper    helper = MultiSelectionHelper::createFromCaller(caller);

    Counter                 i;

    // First we need to get the correct form data source

    for (i = 1; i <= caller.dataSourceCount(); i++)

    {

        formDataSource = caller.dataSource(i);

         if (formDataSource.table() == tableNum(MyTableBuffer))

        {

            break;

        }

    }

    // We then tell the selection helper object to create ranges for the selected records

    helper.createQueryRanges(formDataSource.queryBuildDataSource(), fieldStr(MyTableBuffer, RecId));

    // Now we can traverse the selected records

    myTableBuffer = helper.getFirst();

     while (myTableBuffer)

    {

        info(myTableBuffer.RecId);

         myTableBuffer= helper.getNext();

    }

}