ABAP and observer mode in Design Mode

Reference: skysky

In this chapter, we will introduce the observer mode. The following describes the class diagram of the observer mode example:

First, the code of the test program is provided:

Report zbo_dp_002_re.

* Include file for the class and Interface

Include zbo_dp_002_cl_if.

* Declare data

Data:

* Weather data class reference object

WD type ref to weather_data,

* Define subject interface reference object

Su type ref to subject,

* Concrete observers object

* Crrent condition object

CU Type ref to current_condition_display,

* For Statistics Data Object

SD type ref to statistics_display.

Start-of-selection.

* Create weather data object.

Create object WD.

* Widening cast, make the subject interface reference

* Weather data class

Su? = WD.

* Register concrete obsever to subject interface which

* Point to weather data object

* For concrete observer current condition display

Create object Cu

Exporting WD = Su.

* For concrete observer Statistics Data

Create object SD

Exporting WD = Su.

* Change the weather data, and if the data changed, the subject

* Will inform all of its observers, including current_condition_display

* And statistics_display

Call method WD-> set_measurements

Exporting TEM = '80'

Hum = '80'

Pre = '80 '.

Call method WD-> set_measurements

Exporting TEM = '81'

Hum = '82. 4'

Pre = '80 '.

Call method WD-> set_measurements

Exporting TEM = '79'

Hum = '80'

Pre = '80 '.

The following are three interfaces:

*----------------------------------------------------------------------*

* Include zbo_dp_002_cl_if *

*----------------------------------------------------------------------*

* Interface definition.

* Interface for observer which just have one method, update ()

Interface observer.

Methods:

* When the subject's data changed, it will update observer's data

Update importing temp Type F

Hum Type F

Pre Type F.

Endinterface.

* Interface for subject which used to operating observers

Interface subject.

Methods:

* Register observer to subject

Register_observer importing O type ref to observer,

* Delete observer in subject

Remove_observer importing O type ref to observer,

* Notify Observer that the status or data changed

Notify_observer.

Endinterface.

* Interface for display data

Interface display_element.

Methods:

* When data changed in subject, the observers cocould

* Call this behavior to display data after they receive

* The changed data

Display.

Endinterface.

The following defines a specific topic:

* Define concrete subject

* In our example, we define a weather data object which

* Implement the subject Interface

Class weather_data definition.

Public section.

* Define the interface

Interfaces:

Subject.

Methods:

* The data change method

Measurement_changed,

* Setter method for setting the weather data

Set_measurements

Importing TEM type F

Hum Type F

Pre Type F.

Private section.

* The structure and internal table of observers

Data: Begin of r_observers,

Observer type ref to observer,

End of r_observers.

Data: t_observers like table of r_observers.

* Instance data definition

Data hum Type F.

Data Pre Type F.

Data TEM type F.

Endclass.

* Implement weather data

Class weather_data implementation.

* Implement Interface Method

Method subject ~ Register_observer.

* Get the import observer object

* And add it to observer's table

R_observers-observer = O.

Append r_observers to t_observers.

Endmethod.

Method subject ~ Remove_observer.

* Delete observer

Delete t_observers Where observer = O.

Endmethod.

Method subject ~ Notify_observer.

* Policy observers

Loop at t_observers into r_observers.

* Update observers 'data according to the subject changed data

Call method r_observers-observer-> Update

Exporting temp = TEM

Hum = hum

Pre = pre.

Endloop.

Endmethod.

Method measurement_changed.

* When data changed, inform observer

Call method subject ~ Notify_observer.

Endmethod.

Method set_measurements.

* Set Data of weather

Me-> TEM = TEM.

Me-> hum = hum.

Me-> pre = pre.

Call method measurement_changed.

Endmethod.

Endclass.

The following defines a specific observer: current_condition_display

* Concrete observers

* Display current weather data

Class current_condition_display definition.

Public section.

* Implement two interfaces, observer and display_element

Interfaces:

Observer,

Display_element.

Methods:

* Get the initial concrete subject object

Constructor

Importing WD type ref to subject.

Private section.

Data:

TEM type F,

Hum Type F.

* Concrete subject

Data w_data type ref to weather_data.

Endclass.

Class current_condition_display implementation.

* Update data

Method observer ~ Update.

Me-> TEM = temp.

Me-> hum = hum.

Call method display_element ~ Display.

Endmethod.

* Display data

Method display_element ~ Display.

Write:/'current conditions :'.

Write:/ME-> TEM decimals 2 exponent 0,

'F degrees .'.

Write:/ME-> hum decimals 2 exponent 0,

'% Humidity .'.

Endmethod.

Method constructor.

* Widening cast because WD's type which import is interface subject

* And the me-> w_data's type is weather_data

* And weather data is more specialized than interface subject

Me-> w_data? = WD.

* Register current condition observer to subject

Call method w_data-> subject ~ Register_observer

Exporting o = me.

Endmethod.

Endclass.

The following defines another observer: statistics_display

* Display Statistics Data

Class statistics_display definition.

Public section.

* Implement two interfaces, observer and display_element

Interfaces:

Observer,

Display_element.

Methods:

* Get the initial concrete subject object

Constructor

Importing WD type ref to subject.

Private section.

Data:

Av_temp Type F, "Average Temperature

Mx_temp Type F, "Max temperature

Mi_temp Type F. "Min Temperature

Data: WD type ref to weather_data.

Endclass.

Class statistics_display implementation.

Method constructor.

* Register observer

Me-> WD? = WD.

Call method me-> WD-> subject ~ Register_observer

Exporting o = me.

Endmethod.

Method observer ~ Update.

* Local data definition

* Table Record Number

Data: num type I.

* Local Cal data

Data:

Tav_temp Type F,

Tmx_temp Type F,

Tmi_temp Type F.

* Store all the temperature which setted

Data:

Begin of r_result,

Temp Type F,

End of r_result.

Data: t_result like table of r_result.

* Get the temperature and add it to table

R_result-temp = temp.

Append r_result to t_result.

Describe table t_result lines num.

If num <> 0.

Sort t_result ascending.

* Get min temp

Read Table t_result Index 1 into r_result.

Tmi_temp = r_result-temp.

* Get Max temp

Read Table t_result index num into r_result.

Tmx_temp = r_result-temp.

* Get AVG temp

Loop at t_result into r_result.

Tav_temp = tav_temp + r_result-temp.

Endloop.

Tav_temp = tav_temp/num.

* Update instance variants

Mi_temp = tmi_temp.

Mx_temp = tmx_temp.

Av_temp = tav_temp.

Endif.

* Display result

Call method display_element ~ Display.

Endmethod.

Method display_element ~ Display.

Skip.

Write:/'statistics display :'.

Write:/'average temp: ', av_temp decimals 2 exponent 0.

Write:/'max temp: ', mx_temp decimals 2 exponent 0.

Write:/'min temp: ', mi_temp decimals 2 exponent 0.

Endmethod.

Endclass.