Object Oriented techniques - Example 2 - Display Manager

Hi Biny,

Thanks for the post which is very instructive.

If you are able to add a link to the library cited:

BR_DisplayManager-v02.h

or add a few words about its functionality that would be the 'cherry', as this is new one on me.

👍

@ronbentley1 It's not really a library - just an include file. The attached .zip has all the code files - dump them into an arduino project directory and it should just run (once hardware is set up - it's wired for a Mega). I'll post the other two files here as well so folks don't need to unpack it.

Here is the code for BR_DisplayManager-v02a.h (updated)

#ifndef BR_DisplayManager
#define BR_DisplayManager

#include "Arduino.h"

/* ********** Defined Constants ********** */
#define MAX_DISPLAY_ELEMENTS 10 // Max # of DisplayElements in DisplayManager

/* ******************** DisplayElement ******************** */
// Abstract class for any item that displays information
// regularly as part of the DisplayManager refresh cycle
// Maximum rate of change determined by DisplayManager.frameRate
/* ******************************************************** */
class DisplayElement
{
  public:
      char* DEid;

     // Constructors
     DisplayElement();
     virtual ~DisplayElement();
     
     // Method called by the DisplayManager to refresh display.
     // Must be overridden by subclass.
     // Elapsed time argument is num of ms since Refresh last called
     // which can be accumulated to implement slower changes than the refresh rate.
    virtual void Refresh( unsigned long elapsedTime );
    
  private:
     bool needsRefresh = true; // true if item needs to refresh
};



/* ******************** DisplayManager ******************* */
// A singleton used to contain DisplayElements and control their
// refresh rate, invoking their Refresh() method as required.
/* ******************************************************* */
class DisplayManager
{
  public:
     // Constructors
     DisplayManager();
     DisplayManager( int fRate );

     // FrameRate property in Hz
     int getFrameRate();
     void setFrameRate( int fRate );
     
     // Method called periodically to request a refresh
     // The refresh on the display elements will only be called at frameRate frequency.
     // Returns true if the refresh was done, false if still waiting.
     virtual bool Refresh();

     // Adds instances of DisplayItem to displayElements list and
     // returns a reference to the item.
     void  AddDisplayElement( DisplayElement* dElement_ptr );

     // Removes instances of DisplayItem from the _displayItemsList
     // *** Currently not implemented ***
     void  RemoveDisplayElement( DisplayElement* dElement_ptr );

  private:
     int numDElements; // Current number of display items in array
     DisplayElement* dElement_ptrs [MAX_DISPLAY_ELEMENTS]; // Array pointers to display items.

     int frameRate; // Display refresh rate in Hz
     unsigned long timePerFrame; // duration of wait between refreshes in ms - set by frameRate
     unsigned long previousRefreshTime; // time of previous refresh measured in ms
     unsigned long calcTimeSinceLastRefresh();
};



/* ******************** DigitalLED Class ******************** */
// Manages voltage provided to an LED using a digital pin
// The LED can only be on, off, or blinking - does not dim
/* ********************************************************** */
class DigitalLED: public DisplayElement
{
   public:
      DigitalLED();
      DigitalLED(char* deId, int pinNum, unsigned int cTime, float dCycle);

      // Override DisplayElement.Refresh
      virtual void Refresh(unsigned long elapsedTime) override;

      // Change LED Blink
      void ChangeCycle(unsigned int cTime, float dCycle);

   private:
      void calcCycleTimes(); // uses cycleTime and dutyCycle to calc duty cycle times

      int digitalPINNum; // analog pin number driving the LED
      unsigned int cycleTime; // ms per blink cycle
      float dutyCycle; // % of time spent positive, between 0 and 1

      // Internal state variables
      int timePositivePerCycle; // Time spent high in ms
      int timeNegativePerCycle; // Time spent low in ms

      int timeSinceChange = 0; // Time since state change
      bool ledOn; // TRUE if on, FALSE if off
      
};


#endif // BR_DisplayManager

I'm going to be expanding this to add a few more features and include different types of DisplayElements (AnalogLED, NeoPixelLEDs, LCD, 7Segment LED, yada yada) and tighten up some aspects, but I thought it would lose a lot of its instructional value if I tossed in every kitchen sink.

====================

I cleaned up issues in the comments, and attached is an update (v02a). I corrected the .h and .cpp in the posts above as well. (I can't change the original .ino, - it's missing an "a" on the include statement now, but work from the downloaded .ZIP, which is attached to this post.

@binaryrhyme

Found it!

Posted by: @binaryrhyme

I'm going to be expanding this to add a few more features and include different types of DisplayElements (AnalogLED, NeoPixelLEDs, LCD, 7Segment LED, yada yada) and tighten up some aspects, but I thought it would lose a lot of its instructional value if I tossed in every kitchen sink.

====================

I cleaned up issues in the comments, and attached is an update (v02a). I corrected the .h and .cpp in the posts above as well. (I can't change the original .ino, - it's missing an "a" on the include statement now, but work from the downloaded .ZIP, which is attached to this post.

BR_DisplayManager-v02a-Test.zip

 

OK, again, I commend you for trying to promote and introduce the learning of OOP principles in C++ - it's something I've put forward in the past, but sadly, all I received was member push-back, and no one else supported me to take it further at the time.

I downloaded your code in the .zip file, and had a quick look.
Um... please take a seat with a stiff drink, preferably Jack Daniel's 😀

I won't go too hard on you, but I will point out some fundamental misunderstandings, because they can and have probably mislead some newbies here trying to learn OOP.

Aside from my previous comments, I think this is even far more complex for the newbie to learn.  Here you have introduced inheritance and virtual functions, with a whole bunch of logic and flow that actually detracts (IMO) from the learning process.

1) You claim to have an abstract class, but actually you do not - An abstract class must have at least one pure virtual function, which you do not have, therefore your class is not abstract - Even if it was, you do not inherit from it anyway, so there is no relationship/contract with it.

2) You claim to have implemented a Singleton class, but actually you have no such class. The Singleton class is known as a design pattern, and is mostly frowned upon by software engineers.  For it to be a Singleton class, it must conform to the Singleton design pattern, which in most cases will have a static method with private non copyable constructors and assignment operators, etc...

Additionally, constructor initialization lists are not used, which are the modern way of initializing class member data, and in fact, the only real way you can initialise a base class constructor from a child, so they are an imperative part of OOP.

File management - Header files, include guards - no explanation

Please note, the biggest point here is not that you' re code is right or wrong, but the fact that it's focus is more about the project logic than OOP itself.

I hope I haven't discouraged you to continue to post tutorial material, as that's how we all learn (by debating such material)... please continue, and reach out if you need some help.

Cheers.

@frogandtoad Glad you found it 🙂 Yeh, this is perhaps overestimating the ability of the mean programmer to absorb the concepts without a walkthrough. I worried about that.

Yes on the abstract class not being enforced, but conceptually an abstract class is simply a class that is never instantiated - there are implementation methods that make this impossible, but they would introduce constructs I omitted - I did try to simplify. 🙂

I am well familiar with design patterns, and while a singleton is rarely employed, it is a necessary device when you only need a class that is instantiated only once. As always, "it depends" - and as I said - implementation simplifications were made - but I hear you. I could "enforce" the singleton through coding practices, but I wanted to keep the code simple, while introducing the concept. It is not necessary for a singleton to adhere to an implementation (however well recommended and standard) as the only thing actually required of a singleton is that it only has one instance. 😉

As far as constructor lists go - thank you for the input. I am 60+ years old, and some of the more mod innovations may have escaped me - I am off to my best friend, google. 🙂

Not discouraged at all. Your previous detailed critique pointed out that I hadn't covered the basics sufficiently - and now we are deep in the esoterica of professional practices - but I welcome that - and I suspect I shall, myself, improve. Excellent.

@binaryrhyme Beautiful exchange guys, I for one am learning new words. Still no idea what you are talking about, but I might learn a bit and example code is the best teacher for me as I am not able to read very well any more.

@zander

Posted by: @zander

@binaryrhyme Beautiful exchange guys, I for one am learning new words. Still no idea what you are talking about, but I might learn a bit and example code is the best teacher for me as I am not able to read very well any more.

It's 4:30 AM here and I need some sleep 🙂
I'll post a small example tomorrow regarding the use of abstract classes with polymorphism.

Cheers

@frogandtoad Yeh, that would be cool. I think a lot of folks here want to get to the "next level" and that means a graded ramp of increasing capability and insight would be a good thing.

@frogandtoad I remember a similar example when I was first introduced to OOP. The question I had then was 'What has this to do with payroll, AR, AP, GL etc' Still a valid question, but of course programmers code much more interesting applications today and I do see some applicability but still question how much is gained in $ coding like this.

@zander

Posted by: @zander

@frogandtoad I remember a similar example when I was first introduced to OOP. The question I had then was 'What has this to do with payroll, AR, AP, GL etc' Still a valid question, but of course programmers code much more interesting applications today and I do see some applicability but still question how much is gained in $ coding like this.

You gain a lot, even for projects less than 1000 lines of code.

@frogandtoad Good to know, I will keep my eyes peeled for places to use it.