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Chapter 12

Objects

This chapter describes how to create ToolTalk specs for objects your application creates and manages. Before you can identify the type of objects, you need to define otypes and store them in the ToolTalk Types Database. See Chapter 10, Static Message Patterns for more information on otypes.

The ToolTalk service uses spec and otype information to determine object-oriented message recipients.


Note - Programs coded to the ToolTalk object-oriented messaging interface are not portable to CORBA-compliant systems without source changes.


Object-Oriented Messaging

Object-oriented messages are addressed to objects managed by applications. To use object-oriented messaging, you need to be familiar with process-oriented messaging concepts and the ToolTalk concept of object.

Object Data

Object data are stored in two parts as shown in Figure 12-1.

Figure 12-1 ToolTalk Object Data

One part is called the object content. The object content is managed by the application that creates or manages the object and is typically a piece, or pieces, of an ordinary file: a paragraph, a source code function, or a range of spreadsheet cells, for example.

The second part is called the object specification (spec). A spec contains standard properties such as the type of object, the name of the file in which the object contents are located, and the object owner. Applications can also add their own properties to a spec, for example, the location of the object content within a file. Because applications can store additional information in specs, you can identify data in existing files as objects without changing the formats of the files. You can also create objects from pieces of read-only files. Applications create and write specs to the ToolTalk database managed by rpc.ttdbserverd.


Note - You cannot create objects in files that reside in a read-only file system. The ToolTalk service must be able to create a database in the same file system that contains the object.


A ToolTalk object is a portion of application data for which a ToolTalk spec has been created.

Creating Object Specs

To instruct the ToolTalk service to deliver messages to your objects, you create a spec that identifies the object and its otype. Table 12-1 lists the ToolTalk functions you use to create and write object spec.

Table 12-1 Functions to Create

ToolTalk Function

Description

tt_spec_create(const char *filepath)

Creates spec. Return type is char*.

tt_spec_prop_set(const char *objid, const char *propname, const char *value)

Sets property to specified string value. Return type is Tt_status.

tt_spec_prop_add(const char *objid, const char *propname, const char *value)

Adds string property. Return type is Tt_status.

tt_spec_bprop_add(const char *objid, const char *propname, const unsigned char *value, int length)

Adds byte array property. Return type is Tt_status.

tt_spec_bprop_set(const char *objid, const char *propname, const unsigned char *value, int length)

Sets property to specified byte array value. Return type is Tt_status.

tt_spec_type_set(const char *objid, const char *otid)

Sets object type of spec. Return type is Tt_status.

tt_spec_write(const char *objid)

Writes spec to database. Return type is Tt_status.

To create an object spec in memory and obtain an objid for the object, use tt_spec_create.

Assigning Otypes

To assign an otype for the object spec, use tt_spec_type_set. You must set the type before the spec is written for the first time. It cannot be changed.


Note - If you create an object spec without assigning an otype or with an otype that is unknown to the ToolTalk Types Database, messages addressed to the object cannot be delivered. (The ToolTalk service does not verify that the otype you specified is known to the ToolTalk Types Database.)


Determining Object Specification Properties

You can determine what properties you want associated with an object; you add these properties to a spec. The ToolTalk service recognizes that it is not always possible to store information in your own internal data; for example, the objid for objects in plain ASCII text files. You can store the location of the objid in a spec property and then use this location to identify where the object is in your tool's internal data structures.

The spec properties are also a convenience for the user. A user may want to associate properties (such as a comment or object name) with the object that they can view later. Your application or another ToolTalk-based tool can search for and display these properties for the user.

Storing Spec Properties

To store properties in a spec, use tt_spec_prop_set.

Adding Values to Properties

To add to the list of values associated with the property, use tt_spec_prop_add.

Writing Object Specs

After you set the otype and add properties to an object spec, use tt_spec_write to make it a permanent ToolTalk item and visible to other applications. When you call tt_spec_write, the ToolTalk service writes the spec into the ToolTalk database.

Updating Object Specs

To update existing object spec properties, use tt_spec_prop_set and tt_spec_prop_add specifying the objid of the existing spec. Once the spec properties are updated, use tt_spec_write to write the changes into the ToolTalk database.

When you are updating an existing spec and the ToolTalk service returns TT_WRN_STALE_OBJID when you call tt_spec_write, it has found a forwarding pointer to the object in the ToolTalk database that indicates the object has been moved. To obtain the new objid, create an object message that contains the old objid and send it. The ToolTalk service will return the same status code, TT_WRN_STALE_OBJID, but updates the message objid attribute to contain the new objid. Use tt_message_object to retrieve the new objid from the message and put the new objid into your internal data structure.

Maintaining Object Specs

The ToolTalk service provides the functions to examine, compare, query, and move object specs. Table 12-2 lists the ToolTalk functions you use to maintain object specs.

Table 12-2 Functions to Maintain Object Specifications

Return Type

ToolTalk Function

Description

char *

tt_spec_file(const char *objid)

The name of the file on which the spec is located.

char *

tt_spec_type(const char *objid)

The object type of the spec.

char *

tt_spec_prop(const char *objid, const char *propname, int i)

Retrieves the ith (zero-based) property value as a string.

int

tt_spec_prop_count(const char *objid, const char *propname)

The number of values under this property name.

Tt_status

tt_spec_bprop(const char *objid, const char *propname, int i, unsigned char **value, int *length)

The number of byte array values under this property name.

char *

tt_spec_propname(const char *objid, int i)

The name of the ith property.

int

tt_spec_propnames_count(const char *objid)

The number of properties located on this spec.

char *

tt_objid_objkey(const char *objid)

The unique key of the spec id.

Tt_status

tt_file_objects_query(const char *filepath, Tt_filter_function filter, void *context, void *accumulator)

Queries the database for object specs

int

tt_objid_equal(const char *objid1, const char *objid2)

Checks whether two spec ids are the same.

char *

tt_spec_move(const char *objid, const char *newfilepath)

Moves object spec to a new file.

Examining Spec Information

You can examine the following spec information with the specified ToolTalk functions:

  • Path name of the file that contains the object: tt_spec_file

  • Otype of this object: tt_spec_type

  • Properties stored on the spec: tt_spec_prop or tt_spec_bprop

Comparing Object Specs

To compare two objids, use tt_objid_equal. tt_objid_equal returns a value of 1 even in the case where one objid is a forwarding pointer for the other.

Querying for Specific Specs in a File

Create a filter function to query for specific specs in a file and obtain the specs in which you are interested.

Use tt_file_objects_query to find all the objects in the named file. As the ToolTalk service finds each object, it calls your filter function, and passes it the objid of the object and the two application-supplied pointers. Your filter function does some computation and returns a Tt_filter_action value (TT_FILTER_CONTINUE or TT_FILTER_STOP) to either continue the query, or to quit the search and return immediately.

Example 12-1 illustrates how to obtain a list of specs.


Example 12-1 Obtaining a List of Specifications

/*
 * Called to update the scrolling list of objects for a file. Uses
 * tt_file_objects_query to find all the ToolTalk objects.
 */
int
cntl_update_obj_panel()
{
       static int list_item = 0;
	char *file;
	int i;

	cntl_objid = (char *)0;

	for (i = list_item; i >= 0; i--) {
		xv_set(cntl_ui_olist, PANEL_LIST_DELETE, i, NULL);
	}

	list_item = 0;
	file = (char *)xv_get(cntl_ui_file_field, PANEL_VALUE);
	if (tt_file_objects_query(file,
                                     (Tt_filter_function)cntl_gather_specs,
                                   &list_item, NULL) != TT_OK) {
		xv_set(cntl_ui_base_window, FRAME_LEFT_FOOTER,
		       "Couldn't query objects for file", NULL);
		return 0;
	}

	return 1;
}

 
 
 
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