How to create a Dialog form by extending Runbase class

class CustCreateDialog extends RunBase
{
    DialogField fieldAccount;
    DialogFIeld fieldGroup;

    CustTable   custTable;
    CustTrans   custTrans;
    CustAccount custAccount;
    CustGroupId custGroup;
}

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protected Object Dialog()
{
    Dialog dialog;
    ;

    dialog = super();

    // Set a title for dialog
    dialog.caption( 'Simple Dialog');

    // Add a new field to Dialog
    fieldGroup   =  dialog.addField(extendedTypeStr(CustGroupId), 'Customer Group');
    fieldAccount = dialog.addField(extendedTypeStr(CustAccount),'Customer account');

    return dialog;
}

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public boolean getFromDialog()
{
    // Retrieve values from Dialog
    custAccount = fieldAccount.value();
    custGroup   = fieldGroup.value();
    return super();
}


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public void run()
{
    while select AccountNum, CustGroup from custTable
        where custTable.AccountNum == custAccount
            && custTable.CustGroup == custGroup
        join Voucher, AmountCur, TransDate from custTrans
            where custTrans.AccountNum == custTable.AccountNum
       
    if (custTable)
    {
        // Shows retrieved information
        info( strFmt('%1 -- %2 -- %3 --- %4 ---%5' , custTable.AccountNum, custTable.name(), custTrans.Voucher, custTrans.AmountCur, custTrans.TransDate));
    }
    else
    {
        error( 'Customer Account not found!');
    }
}

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public static void main(Args _args)
{
    CustCreateDialog custCreate = new CustCreateDialog();

    // Prompt the dialog, if user clicks in OK it returns true
    if (custCreate.prompt())
    {
        custCreate.run();
    }
}