Write a lookup code in form level for MainAccount,name and BankAccount,name .

public void lookup(FormControl _formControl, str _filterStr)
{
    Query                                 query          = new Query();
    QueryBuildDataSource     queryBuildDataSource;
    QueryBuildRange             queryBuildRange;
    SysTableLookup               sysTableLookup;
    ;
    switch(unitMasterSetup.AccountType)
    {
        case Accounttype::Ledger :
            sysTableLookup =     SysTableLookup::newParameters(tableNum(MainAccount),_formControl);
            sysTableLookup.addLookupField(fieldNum(MainAccount, MainAccountId));
            sysTableLookup.addLookupField(fieldNum(MainAccount, Name));
            queryBuildDataSource = query.addDataSource(tableNum(MainAccount));
            queryBuildDataSource.addSelectionField(fieldNum(MainAccount, LedgerChartOfAccounts));
            MainAccount::addSecureRangeForChartOfAccounts(queryBuildDataSource);
            sysTableLookup.parmQuery(query);
            sysTableLookup.performFormLookup();
            break;

        case  Accounttype::Bank :
            sysTableLookup =  SysTableLookup::newParameters(tableNum(BankAccountTable), _formControl);
            sysTableLookup.addLookupField(fieldNum(BankAccountTable, AccountID));
            sysTableLookup.addLookupField(fieldNum(BankAccountTable, Name));
            queryBuildDataSource = query.addDataSource(tableNum(BankAccountTable));
            sysTableLookup.parmQuery(query);
            sysTableLookup.performFormLookup();
            break;
        Default :   Error("Unknown account type.");
    }
}