Using the Field Topic

In a conversation with USoft Developer about the Field topic, you may specify a particular field as an item. This field must be in a window that is currently open. If you request a value from a field, you receive the value from the current record. If the end-user moves to the next record and you request the value of the same item again, you receive the value of the new record.

To refer to a field value, use ObjectNamePlural.ColumnName, where ObjectNamePlural is the Object Name Plural as defined in the repository, and ColumnName is the name of the column underlying the current field.

You may request the current value of an item, poke a new value into it and start an advise loop for it. Your client receives notification of a change in the item value whenever the end user changes a value in the field referred to in the item specification. This change does not necessarily occur in the record which was the current record at the moment that the advise loop was started.

To start a conversation about the Field topic:

·	Call the DdeConnect() function from the Windows DDL library:

HSZ hszService;

HSZ hszTopic;

HCONV hConv = (HCONV)NULL;

hszService = DdeCreateStringHandle(

idInst,

(LPCSTR)"USoftDeveloper",

CP_WINANSI);

hszTopic = DdeCreateStringHandle(

idInst,

(LPCSTR)"Field",

CP_WINANSI);

hConv = DdeConnect(

idInst,

hszService,

hszTopic,

NULL);

To retrieve the value of a particular field:

·	Send a DDE request for a particular item to the USoft DDE server.

To retrieve the current value in the Name field in the Persons window, the item name is "persons.name", where Persons is the Object Name Plural and Name is the name of the column underlying the Name field.

To send a request for the "persons.name" item to the USoft DDE server:

·	Write the following procedure:

HSZ hszItem;

HDDEDATA hData;

DWORD lpcbData;

LPSTR pData;

char buf[BUFSIZ];

hszItem = DdeCreateStringHandle(

idInst,

(LPCSTR)"persons.name",

CP_WINANSI);

hData = DdeClientTransaction(

(LPBYTE)NULL,

hConv,

hszItem,

CF_TEXT,

XTYP_REQUEST,

DDE_TIMEOUT,

NULL);

pData = (LPSTR)DdeAccessData(

hData,

&lpcbData);

lstrcpy(buf, pData);

To poke data back into the "persons.name" item:

·	Write the following procedure:

hszItem = DdeCreateStringHandle(

idInst,

(LPCSTR)"persons.name",

CP_WINANSI);

pData = (LPSTR) "New value";

hData = DdeCreateDataHandle(

idInst,

pData,

lpcbData,

0L,

hszItem,

CF_TEXT,

0);

DdeClientTransaction(

(LPBYTE) hData,

-1,

hConv,

hszItem,

CF_TEXT,

XTYP_POKE,

DDE_TIMEOUT,

NULL);