Object ‘Method’¶

Symbol:

Keyword: METHOD

Methods are an extension of the IEC 61131-3 standard and a tool for object-oriented programming that is used for data encapsulation. A method contains a declaration and an implementation that includes a series of statements. However, unlike a function, a method is not an independent POU, and it is assigned to a function block or program. You can use interfaces for the organization of methods.

You can add a method below a program or a function block. Click Project ‣ Add object ‣ Method to open the Add method dialog.

Declaration:

The variables of a method contain temporary data and are valid only during the execution of the method (stack variables). All variables that are declared and implemented in a method are reinitialized each time the method is called.
Methods that are declared in an interface may define input, output and VAR_IN_OUT variables and may not contain any implementation.
Like functions, methods can have additional outputs. You must assign these additional outputs in the method call.

Implementation:

Access to function block instances or program variables is permitted in the implementation of the method.
The THIS pointer allows for access to its own function block instance. Therefore, the pointer is permitted only in methods that are below a function block.
A method cannot access VAR_TEMP variables of the function block.

Hint

If you copy a method below a POU and add it below an interface, or move the method, then the contained implementation is removed automatically.

Dialog Add method ¶

Function: Configures the method that is added by closing the dialog.

Call: Project ‣ Add object ‣ Method ; context menu

Requirement: A program (PRG) or a function block (FUNCTION_BLOCK) is selected in the POUs view or the Devices view.

Name	Example: `meth_DoIt`
Return type	Default type or structured type of return value Example: `BOOL`
Implementation language	Example: Structured Text (ST)
Access specifier	Controls access to data. PUBLIC or not specified: Access is not restricted. PRIVATE: Access is restricted to the program, function block, or GVL. The object is marked as `(private)` in the POU or device view. The declaration contains the keyword `PRIVATE`. PROTECTED: Access is restricted to the program, function block, or GVL with its derivations. The declaration contains the keyword `PROTECTED`. The object is marked as `(protected)` in the POU or device view. INTERNAL: Access to the method is restricted to the namespace (library). The object is marked as `(internal)` in the POU or device view. The declaration contains the keyword `INTERNAL`.
Add	Adds a new method below the selected object.

Special methods of a function block ¶

`FB_Init`	Declarations are automatically implicit. Explicit declaration is also possible. Contains initialization code for the function block, as is defined in the declaration part of the function block.
`FB_Reinit`	Explicit declaration is necessary. After the instance of the function block is copied (as during an online change): calls and reinitializes the new instance module.
`FB_Exit`	Explicit declaration is necessary. Call for each instance of the function block before a new download or a reset or during an online change for all shifted or deleted instances.
Attributes and interface attribute	Provides `Set` and/or `Get` accessor methods.

Input assistance when creating inheriting blocks ¶

When you do object-oriented programming and want to use inheritance for blocks, you have the following support: When you insert a method, action, etc. below an inherited block, the Add Object dialog box includes a combo box with a list of methods, actions, etc. used in the base block. In this way, you can easily accept a method definition of the base and adapt it accordingly for the inherited method of the block. Methods and attributes with the PRIVATE access modifier are not available in this selection because they should not be inherited. When accepted into the inherited block, methods and attributes with the PUBLIC access modifier automatically have a blank access modifier field. (Functionally, this means the same thing.)

Object ‘Method’¶

Dialog Add method¶

Special methods of a function block¶

Input assistance when creating inheriting blocks¶

Dialog Add method ¶

Special methods of a function block ¶

Input assistance when creating inheriting blocks ¶