Chapter 5—Object Oriented Programming

This chapter discusses the object-oriented features used in Omnis Studio, including inheritance, custom properties and methods, and creating and using object classes and external objects.

Note that most of the example code in this chapter is generic and can be applied to all programming tasks; however, some of the example code may relate to window classes only, but the code may be easily adapted to work with remote forms.

Inheritance

When you create a new class, you can derive it from an existing class in your library. The new class is said to be a “subclass” of the existing class, which is in turn a “superclass” of the new class. You can make a subclass from all types of class, except schema, query, remote menu, code classes, file or search classes. The general rule is that if you can open or instantiate a class, such as a remote form, then you can make a subclass of that type of class. Omnis does not support mixed inheritance, that is, you cannot make a subclass of one type from another type of class.

Why should I use inheritance?

When you make a subclass, by default, it inherits all the variables, methods, and properties of its superclass. For example, remote form subclasses inherit all the fields and objects, as well as all the methods, from the remote form superclass. Therefore, inheritance saves you time and effort when you develop your application, since you can reuse the objects, variables, and methods from a superclass. When you make a change in a superclass, all its subclasses inherit the change automatically. From a design point of view, inheritance forces uniformity in your UI by imposing common properties, and you get a common set of methods to standardize the behavior of the objects in your library.

Making a Subclass

You can make subclasses from the following types of class:

You can make subclasses from the following types of class, but they apply to desktop apps only (so are not available in the Community Edition):

To make a subclass

When you make a subclass Omnis creates a new class derived from the selected class. The new class inherits all the objects, variables, and methods from its superclass. Omnis supports up to 10 superclass levels, that is, a single class can inherit objects from up to ten other superclasses that are directly in line with it in the inheritance tree. If you create further levels of subclass they do not inherit the objects from the superclasses at the top of the tree.

You can view and edit a subclass, as you would any other class, by double-clicking on it in the Browser. When you edit the methods for a subclass in the method editor, you will see its inherited variables and methods shown in a color. When you view the properties of a subclass its inherited properties are shown in a color in the Property Manager. You can set the color of inherited objects using the inheritedcolor Omnis preference. Note that all the Appearance and Action properties for a window are inherited too.

Standard properties for the class, such as the window name and class type, are not inherited, neither are the grid properties. The properties to do with the general appearance of the window, such as title and hasmenus, are inherited and shown in a color, which defaults to bright blue. You cannot change inherited properties unless you overload them: their values are grayed out in the Property Manager. If you change the properties of the superclass, the changes are reflected in the subclass when you next open it in design mode.

There are some general properties of a class that relate to inheritance, as follows:

Property Description
$superclass the name of the superclass for the current class; the superclass can be in another library, in which case the class name is prefixed with the library name
$inheritedorder for window classes only, determines where the inherited fields appear in the tabbing order: by default inherited fields appear before non-inherited fields on your window
$issupercomponent if true the class is shown in the Studio Browser as a superclass
$componenticon icon for the superclass when it is shown in the Studio Browser

Window Status Bar

A window subclass can inherit window status bar panes from a superclass. In design mode, when you right-click on the status bar, the Inherit option allows you to inherit the status bar panes from a superclass (the option allows you to toggle the panes on or off). When inherited, you cannot change any of the pane or bar properties in design mode, and these properties are displayed in the Property Manager using the inherited colour.

Subclass Editors

Class editors for subclasses update immediately when the superclass has been changed, so you do not have to close and re-open a subclass to see the changes made to the superclass.

Making a Subclass Manually

You can set the superclass property for a class manually, to make it a subclass of the specified class, either using the notation or in the Property Manager.

However, when you make a subclass in this way it does not inherit any of the properties of the superclass: only objects are inherited from the superclass. You have to open the Property Manager and inherit the properties manually using a context menu.

To inherit a property manually

If the property cannot be inherited the context menu will display Cannot Inherit and will be grayed out. If the class does not have a superclass the inheritance context menu does not appear or is grayed out.

To inherit a method manually

When you inherit a method in this way, Omnis will delete the current method. Any comments in the inherited method will be shown on the left-hand side of the ‘Notes’ tab in the Variable pane in the Method Editor.

Inherit or Override method Shortcut

The Inherit method or Override method options are present in the method editor Modify menu when it is appropriate to include the command. Both have the shortcut Ctrl+Shift+I to inherit or override the current method.

Overloading Properties, Methods, and Variables

Having created a class from another class using inheritance you can override or overload any of its inherited properties, methods, and variables in the Property Manager or the Method Editor as appropriate. All inherited objects are shown in a color. To overload an object, you can Right-click on the object and select Overload from the object’s context menu.

(Note that for windows, menus, and toolbars you cannot overload or delete inherited fields, menu lines, or toolbar controls. If you don’t want certain objects to be displayed in a subclass you can hide them temporarily at runtime using the notation.)

To overload a property

When you overload a property, its inherited value is copied to the class and becomes editable in the Property Manager. You can overload any number of inherited properties in the class and enter values that are local to the class.

To reverse overloading, you Right-click on a property and select Inherit Property: the local value will be overwritten, and the value inherited from the superclass will appear in the Property Manager.

To override a method

When you override a method it becomes like a non-inherited method in the class, that is, you can select it and add code to it.

To reverse this process and inherit the method with the same name from the superclass, you can right-click on the method and select Inherit Method: the code in the non-inherited method will be deleted and the inherited method will now be in place. Alternatively, if you override a method and then delete the local one, the inherited method will reappear when you close and reopen the class.

To override a variable

When you override a variable it becomes like a non-inherited variable in the class and is only visible in that class.

To reverse this process and inherit the variable with the same name from the superclass, you can Right-click on the variable and select Inherit Variable.

Inheritance Tree

The Inheritance Tree shows the superclass/subclass structure of the classes in your library. All classes below a particular class in the hierarchy are subclasses of that class. When you select a class in the Browser and open the Inheritance Tree it opens with that class selected, showing its superclasses and subclasses above and below it in the tree.

To open the Inheritance Tree for a class

Showing Superclasses in the Studio Browser

You can show any class that supports inheritance in the Studio Browser by setting its $issupercomponent property to kTrue. You can specify the icon for a superclass by setting its $componenticon property. If you create a class from a superclass displayed in the Studio Browser, the new class will be a subclass of the class in the Studio Browser automatically.

To make a subclass from a supercomponent

At this stage, all the supercomponents of that type (i.e. classes that have their $issupercomponent set to kTrue) should be displayed in the wizard.

Such supercomponents will only appear in the Studio Browser if the library containing it is open, since the class actually remains in your library and is only displayed in the Studio Browser.

Note that classes that appear in the Studio Browser in this way cannot be made the default object for that class.

Inheritance Notation

You can use the $makesubclass() method to make a subclass from another class. For example

Do  $windows.Window1.$makesubclass('Window2') Returns ItemRef
# creates Window2 which is a subclass of Window1 in the
# current library, ItemRef contains a reference to the new class

You can test if the current class can be subclassed by testing the $makesubclass() method with the $cando() method, as follows

If  $cclass.$makesubclass().$cando()
  Do $cclass.$makesubclass(sClass) Returns ItemRef
  # creates a subclass of the current class
  ...

The $makesubclass() method has a Boolean optional second argument (bAddLibPrefixForClib, default kFalse), which when kTrue, causes the $superclass property of the new subclass to include the library prefix for the current library.

You can test if a particular class is a superclass of another class using the CLASS.$isa(SUPERCLASS) method as follows

Do  $windows.window2.$isa($windows.window1Returns lresult
# returns true if window1 is a superclass of window2

You can change the superclass of a class by reassigning $superclass

Do  $cclass.$superclass.$assign('DiffClassName') Returns lresult

You can test if a property can be inherited using

Do  $cclass.$style="font-variant: small-caps;">PropertyName.$isinherited.$canassign() Returns lresult

If a property can be inherited, you can overload or inherit the property by assigning $isinherited. For example, to overload a property

Do  $cclass.$style="font-variant: small-caps;">PropertyName.$isinherited.$assign(kFalseReturns lresult

A superclass can be in a different library to a subclass. If you open an instance of a subclass when the superclass is not available, perhaps because the library the superclass belongs to is not open or has been renamed, a kerrSuperclass error is generated.

Libraryname prefix for subclasses

By default, Omnis does not prefix $superclass with the library name (if both classes are in the same library).  You can manually change the $superclass property to include the library name if you wish.

Calling Properties and methods

When a property or method name is referenced in a subclass, Omnis looks for it first in the subclass and progressively up the chain of superclasses in the inheritance tree for the current library. Therefore, if you haven’t overridden the property or method in the subclass, or at any other level, the property or method at the top of the inheritance tree will be called. For example, the following command in a subclass

Do  $cinst.$MethodName()
# will call $MethodName() in its superclass

However, if you have overridden a property or method in the subclass the method in the subclass is called. You can still access the inherited property or method using the $inherited property. For example, assuming $MethodName() has been overridden in the subclass

Do  $cinst.$inherited.$MethodName()
# will call the superclass method

Do $windows.MySubWin.$MethodName().$inherited
# will call $MethodName() in the superclass

$inherited is present at the top level, and in $cinst for all types of instance (while $default is available for table instances only).

Referencing Variables

When a variable is referenced in a subclass, Omnis looks for its value first in the subclass and progressively up the chain of superclasses in the inheritance tree for the current library. Therefore, if you haven’t overridden the variable in the subclass, or at any other level, the value at the top of the inheritance tree is used.

However, if you have overridden a variable in the subclass the value in the subclass is used. You can access the inherited variable using $inherited.VarName, in which case, the value at the top of the inheritance tree is used.

A superclass cannot use the instance and class variables of its subclasses, although the subclass can pass them as parameters to superclass methods. References to class and instance variables defined in a superclass are tokenized by name and the Remove Unused Variables check does not detect if a variable is used by a subclass. If an inherited variable does not exist, its name is displayed as $cinst.VarName in design mode and will create a runtime error.

Inherited Fields and Objects

All inherited window fields on a window subclass are included in the $objs for an instance. Since some field names may not be unique, when $objs.name is used Omnis looks first in the class containing the executing method, then in the superclasses and lastly in the subclasses. The $objs group for report fields, menu lines, and toolbar controls behave in the same way as window fields.

You should refer to fields at runtime by name, since at runtime Omnis assigns artificial $idents to inherited fields. The $order property of a field may also change at runtime to accommodate inherited fields into the tabbing order.

Do inherited Command

You can use the Do inherited command to run an inherited method from a method in a subclass. For example, if you have overridden an inherited $construct() method, you can use the Do inherited command in the $construct() method of the subclass to execute the $construct() method in its superclass. You could use this command at the end of the $construct() method in the subclass to, in effect, run the code in the subclass $construct() and then the code in the superclass $construct() method.

Inherited Object Notation

You can access the methods of inherited objects in remote forms, windows, menus, toolbars and reports in your Omnis code. Inherited objects are exposed as a new group within the notation group called $inheritedobjs. The members of this group are the inherited objects from all of the superclasses of the class.

Each member of the $inheritedobjs group has three properties: $name, $ident and $isorphan (true when the object no longer belongs to a superclass, but has methods so it cannot be removed without developer approval). In addition, each member has a child $methods group which are the methods implemented in the class for the inherited object. This is just like any other methods group, and methods can be manipulated as you would expect. To override a method from the superclass, simply add a method with the same name as the inherited object method. To inherit a method, delete the method with the same name from the inherited object methods.

Object Classes

Object classes let you define your own structured data objects containing variables and methods. You can create an object variable based on an object class which contains all the variables and custom methods defined in the class. When you reference an object variable an instance of the object class is created containing its own set of values. You can store an object variable instance and its values on a server database (or Omnis datafile). The structure and data handling capabilities of the object instance is defined by the types of variables you add to the object class; similarly, the behavior of an object variable is defined by the methods you add to the object class.

Object classes have the general properties of a class and no other special properties. They can contain class and instance variables, and your own custom methods. You can make a subclass from an object class, which inherits the methods and variables from the superclass.

The HTTP Push example app in the Hub in the Studio Browser uses Object classes to create an HTTP Worker object; see this example app for code using object classes.

To create an object class

Alternatively, you may want to create an object class using one of the wizards. In this case, you should click on Class Wizard, then Object, and select one of the wizards.

When you modify an object class, Omnis opens the method editor for the class. This lets you add variables, and your own custom properties and methods to the class.

When you have set up your object class you can create any other type of Omnis variable based on your object class: an object variable has type Object and its subtype is set to the name of your object class. For example, you can create an instance variable of Object type that contains the class and instance variables defined in the object class. When you reference a variable based on an object class you create an instance of that object class that belongs to the current task at the point of their creation (this provides consistency with object instances created via $new). You can call the methods in the object class with the notation ObjVarName.$MethodName(), where $MethodName() is any custom method you have defined in the object class.

You can store object variable instances in a server database that stores binary values (or an Omnis data file). When you store an instance of an object variable in a database, the value of all its contained instance variables are also stored. When the data is read back into memory the instance is rebuilt with the same instance variable values. In this respect you can store a complete record or row of data in an object variable.

You can store object instances in a list. Each line of the list will have its own instance of the object class. Object instances stored in a task, instance, local, or parameter variable belong to the same task as the instance containing that variable. Similarly object instances stored in a list or row belong to the same task as the instance containing the list or row variable. All other object instances have global scope and are instantiated by the default task and belong to the default task.

You cannot make an object instance a private instance. If you delete the object class an object variable uses, the object instance will be empty.

An object instance stored as a class variable in a task is destroyed as soon as its original task is destroyed.

To add variables and methods to an object class

If you right click on an object variable, and use the Variable <name>... entry in the context menu, the variables list window opens, initially showing instance variable values.

Missing Object Variables

An error is generated when you open a library that tries to construct an Object variable and the Object class it is based on does not exist or is in a library that is not open. In this scenario, you will get a runtime error and execution blocks with the following error:

E100101: Class not found when constructing an object variable

The class name is TESTB.oTestB
Either the class does not exist or it has the wrong type e.g. remote object

In versions prior to Studio 10 in this case, you would have received the error “Class not found”, but code execution would have continued which may have led to further errors in the application.

$cando and Error Handling

Since Studio 10.1. the default behavior when Omnis attempts to construct an object variable when its class does not exist, is to report a debugger error when code attempts to use the object, e.g. via $cando. From Studio 10.2, you can override this behavior, for example, $cando will return kFalse for notation like iObject.$message.$cando.

To override this behavior, you can use the $nofatal property of object variables:

Calculate iObject.$nofatal as  kTrue

When using $cando after setting $nofatal to kTrue, the $cando will return false.

Variable Count

The $usage property reports the current number of object variables that are sharing the underlying external component object. A NULL value means the object is neither an external component object, nor is it subclassed from an external component object.

Note that copies of the object such as $statementobject and $sessionobject contribute to the count.

Using Object Classes

This section describes an invoices example and uses an object class and simple invoices window; it is intended to show what you can do with object classes, not how to implement a fully functional invoices application. You can create the data structure required for an invoice by defining the appropriate variables and custom methods in an object class.

The following example uses an object class called o_Invoice, which contains the variables you might need in an invoice, such as the invoice ID, quantity, value, and a description of the invoice item. The o_Invoice object class also contains any custom methods you need to manipulate the invoice data, such as inserting or fetching invoices from your database. The methods in the object class contain the following code

# $SaveInvoice() method contains
# local var lv_InvoiceRow of type Row and
# local var lv_Bin of type Binary and
# parameter var pv_Object of type Field reference
Do lv_InvoiceRow.$definefromtable(t_Invoices)
Calculate lv_bin as pv_Object
Calculate lv_InvoiceRow.InvoiceObject as lv_bin
Do lv_InvoiceRow.$insert() Returns #F
# $SelectInvoice() method contains
# local var lv_Row of type Row
Do lv_Row.$definefromtable(t_Invoices)
Do lv_Row.$select()
Do lv_Row.$fetch() Returns #S1
Quit method lv_Row.InvoiceObject
# $FetchInvoice() method contains
# local var lv_Row of type Row
Do lv_Row.$definefromtable(t_Invoices)
Do lv_Row.$fetch()
Quit method lv_Row.Inv_Object
# $total() method

Quit method iv_QTYiv_Value

The invoice window can contain any fields or components you want, but would contain certain fields that reference the instance variables in your object class, and buttons that call the methods also in your object class.

The invoice window contains no class methods of its own. All its functionality is defined in the object class. The window contains a single instance variable called iv_Invoice that is based on the o_Invoice object class.

The instance variable would have the type Object and its subtype is the name of your object class, o_Invoice in this case. If the object class is contained in another library, the object class name is prefixed with the library name.

When you open the invoice window an instance of the object class is created and held in iv_Invoice. Therefore you can access the instance variables and custom methods defined in the object class via the instance variable in the window; for example, iv_Invoice.iv_QTY accesses the quantity value, and iv_Invoice.$SaveInvoice() calls the $SaveInvoice() method. Each field on the invoice window references a variable in the object class; for example, the dataname of the quantity field is iv_Invoice.iv_QTY, the dataname of the item or description field is iv_Invoice.iv_Item, and so on.

The buttons on the invoice window can call the methods defined in the object class, as follows.

# $event() method for the Select button
On evClick
  Do iv_Invoice.$SelectInvoice(iv_Invoice.iv_IDReturns iv_Invoice
  Do $cwind.$redraw()

# $event() method for the Fetch button
On evClick
  Do iv_Invoice.$FetchInvoice Returns iv_Invoice
  Do $cwind.$redraw()

# $event() method for the Save button
On evClick
  Do iv_Invoice.$SaveInvoice(iv_Invoice

When you enter an invoice and click on the Save button, the $SaveInvoice() method in the object class is called and the current values in iv_Invoice are passed as a parameter. The $SaveInvoice() method receives the object instance variable in the parameter pv_Object and executes the following code

Do  lv_InvoiceRow.$definefromtable(t_Invoices)
Calculate lv_bin as pv_Object
Calculate lv_InvoiceRow.InvoiceObject as lv_bin
Do lv_InvoiceRow.$insert() Returns #F

The row variable lv_InvoiceRow is defined from the table class t_Invoices which is linked to the schema class called s_Invoices which contains the single column called InvoiceObject. The binary variable lv_bin, which contains the values from your object instance variable, is assigned to the row variable. The standard $insert() method is executed which inserts the object variable into your database. The advantage of using an object variable is that all the values for your invoice are stored in one variable and they can be inserted into a binary column in your database via a single row variable. If you want to store object variables in an Omnis database you can create a file class that contains a single field, called InvoiceObject for example, that has Object type, rather than Binary, and use the appropriate methods to insert into an Omnis data file.

Libraryname prefix for object variables

There is an "Include library prefix" check box on the object class selection dialog. This allows you to add the library name to the object class name for the variable, but when the object class is in the same library you don’t need to add the libraryname prefix.

Dynamic Object Instances

The object class has a $new() method that lets you create an object instance dynamically and store it in an object variable, for example

Do  $clib.$objects.objectclass.$new(parm1,parm2,...) Returns objectvar

where parameters parm1 and parm2 are the $construct() parameters for the object instance. When the instance is assigned, any existing instance in the object variable is destroyed. It would be normal practice to put no class in the variable pane for object variables which are to be set up dynamically using $new(), but there is no class checking for instance variables so no error occurs if the class shown in the variable pane is different from the class of the new instance.

You can do a similar thing with an external function library if it contains instantiable objects, such as Fileops. For example

Do  Fileops.$objects.fileops.$new() Returns objectvar
Do objectvar.$openfile(pFilename)

The following example uses an Object variable ivSessionObj which has no subtype defined in the method editor. When this code executes ivSessionObj is instantiated based on the object class SessionObj which was created using the Session Wizard in Omnis. Once the object instance exists the $logon() method is called.

Do  $clib.$objects.SessionObj.$new() Returns ivSessionObj
# runs $construct() in the SessionObj object class

Do ivSessionObj.$logon()
# runs the $logon() method in SessionObj

Self-contained Object Instances

Object classes have the $selfcontained property. If set to kTrue the class definition is stored in all instances of the object class. An instance of such an object class is disconnected from its class and instead relies on its own class data for method and instance variable definitions. When the object instance is stored on disk the class definition is stored with the instance data and is used to set up a temporary class whenever the instance is read back into memory. Any changes to the original object class have no effect on existing instances, whether on disk or in memory.

Once an instance is self-contained it is always self-contained, but you can change its class definition by assigning to $class, for example

Do  file1.objvar1.$class.$assign($clib.$objects.objectclass1) 

causes the class definition stored inside objvar1 to be replaced by the current method and variable definitions for objectclass1. The instance variable values are maintained provided the new instance variable definitions are compatible with the old ones (Omnis can handle small changes in the type of variables but won’t carry out substantial conversions). Note that the old instance variables are matched to the new ones by $ident and not by name, so to avoid problems the new class should be a descendant of the original class with none of the original variables having been deleted.

Only the main class is stored with the object instance, inheritance is allowed but any superclasses must exist in open libraries whenever the instance is present in memory. Assigning to $class does not change the superclass structure of self-contained instances.

Object References

The Object reference data type provides non-persistent objects that you can control using notation. Non-persistent means that objects used in this way cannot be stored on disk, and restored for use later.

You can use the Object reference data type with local, instance, class and task variables. Object references have no subtype. To create a new Object instance, referenced by an Object reference variable, you use the methods $newref() and $newstatementref(). These are analogous to the $new() and $newstatement() methods used to create object variables, and they can be used wherever $new() and $newstatement() can be used. When created, an object reference will belong to the current task, and are no longer valid after the task closes.

Once you have associated an Object instance with an Object reference variable, you can use it to call methods just like you would with an Object variable.

The instance associated with an object reference variable will be destroyed in the following circumstances:

Until one of these occurs, Object reference variables can be passed as parameters, copied, stored in a list column, and so on. All copies of the variable address the same single instance of the object. As soon as the object is deleted, other references to the object become invalid. Prior to deleting the object, Omnis calls the destructor method.

Note that this approach means that you must delete objects when you have finished with them, otherwise significant memory and resource leaks can occur.

There is also a method $listrefs() which you can call to list the instances of an object class, external object, or in fact all instances created in this way. This is useful both for leak-checking, and for clean-up.

You can use $newref() in conjunction with session pools. The only differences are that $deleteref() returns the object instance to the pool, rather than destroying it, and $listrefs() does not include objects from a session pool.

There are two further methods that can be used with object reference variables. $copyref() creates an object instance which is a copy of the instance referenced by the variable, and $validref() returns a Boolean which is true if and only if the variable references a valid object instance. Note that if $copyref() takes a copy of a DAM session object, both copies reference the same DAM session.

The method $objref() can also be used. If there is an object reference associated with the instance, the method returns the object reference, otherwise returns #NULL, that is, the object MUST have been created with a $newref().

Constructing new objects

…from an object class

Calculate myObjectReference as  $clib.$objects.myObject.$newref("Test")

…from an external object

Calculate myObjectReference as  $extobjects.ODBCDAM.$objects.ODBCSESS.$newref()

…from a session object

Calculate myObjectReference as  mySessionObjectReference.$newstatementref()

…storing the reference in a list column of type Object reference

Do  theList.$add($extobjects.ODBCDAM.$objects.ODBCSESS.$newref())

Listing instances created using an Object reference

…instances of an object class

Calculate myList as  $clib.$objects.myObject.$listrefs()

…instances of an external object

Calculate myList as  $extobjects.ODBCDAM.$objects.ODBCSESS.$listrefs()

…all instances

Calculate myList as  $listrefs()

Destructing objects

…using an object reference variable:

Do  myObjectReference.$deleteref() ## Calls the destructor of the object instance

…all instances referenced by a list column of type Object reference:

Do  myList.$sendall($ref.1.$deleteref())

…using the $listrefs() method:

Do  $extobjects.ODBCDAM.$objects.ODBCSESS.$listrefs().$sendall($ref.1.$deleteref())
Do $libs.DAMTEST.$objects.Doracle8.$listrefs().$sendall($ref.1.$deleteref())

Testing an object reference for validity

…using an object reference variable:

If  myObjectReference.$validref()

…using a list column of type Object reference:

If  myList.1.myObjRef.$validref()

Copying an object reference

…using an object reference variable:

Calculate objectReference as  myObjectReference.$copyref()

…using a list column:

Calculate objectReference as  myList.1.myObjRef.$copyref()

External Objects

External objects are a type of external component that contain methods that you can use by instantiating an object variable based on the external object. External objects can also contain static functions that you can call without the need to instantiate the object. These functions are listed in the Catalog under the Functions pane.

Some external objects are supplied with Omnis Studio; these include equivalents to the FileOps and FontOps externals, a Timer object, as well as the multi-threaded DAMs. Writing your own external objects is very similar to writing external components. The FileOps and FontOps functions are documented in the Omnis Help.

External objects are created and stored in component libraries in a similar manner to external components, and in future releases are intended to replace external functions and commands, although to maintain backward compatibility, the old external interface is still supported at present.

External object libraries are placed in the XCOMP folder, along with the visual external components. They must be loaded in the same way as external components using the External Components option, available in the Browser when your library is selected.

Using External Objects

You can add a new object in the method editor by inserting a variable of type Object and using the subtype column to select the appropriate external object. You can click on the subtype droplist and select an external object from the Select Object dialog. This dialog also appears when you create an object elsewhere in Omnis. An icon in the variable subtype cell shows whether the variable is based on an object class or an external object.

When an instance of the external object has been constructed, you can inspect its properties and methods using the Interface manager.

To use the object’s methods in your code, you can drag the method you require from the Interface Manager into the Code Editor.

For some objects it is important to note that for the Interface manager to interrogate an object it will need to be constructed. For example, if the Interface Manager was used on an Automation object, the Automation server needs to be started.

External objects are contained in the notation group $extobjects, which you can omit from notation.

External Object Events

External objects do not support events in the GUI sense. They can however define notification methods which they call when certain events occur.

You can subclass an external object and then override the notification method so your code is informed of the event. The Timer object supplied in Omnis is an example of this. To subclass an object, you can either set the superclass property in the Property Manager, or use the New Subclass Object wizard available in the Browser (using the Class Wizard>>Object option).

External Object Notation

All the components available to Omnis are listed in the $root.$components group. Individual components have their own methods, in addition to the $cmd() method which allows you to send a component specific command to the component or object.

The following examples show some commands that you can send to an ActiveX component to manage timeouts:

Do  $components.ActiveX.$cmd("RequestPendingTimeout",10000)
# Set timeout in milliseconds

Do $components.ActiveX.$cmd("ServerBusyTimeout",10000)
# Set timeout in milliseconds

Do $components.ActiveX.$cmd("ResponseDialog",kFalse)
# Prevent response dialog from appearing

Do $components.ActiveX.$cmd("BusyDialog",kFalse)
# Prevent busy dialog from appearing