Advice App architecture for working with Canvas

[Robert_Livingston]

@Yann_DUPONT

My app throws me away

Anthony’s interpretation may be correct, but as a rule, when asking questions on the forum try and be as specific as possible. “My app throws me away” is not specific. If there is an error message, you want to specify what it is, and when you see it. Basically be explicit as possible as to what happened.

[Robert_Livingston]

@Yann_DUPONT

My second question is regarding adding 2Dobjects in my Canvas. If I tell my code to fire the paint event the whole canvas is redrawn, all previous elements are erased and just the new one is drawn. Do I have to parse throught ALL the dictionnary everytime I want to add, remove or refresh my Canvas?

You do have to go through all the elements in the Dictionary that are specifying Object2D’s on your canvas. Anthony is suggesting one sophisticated methodology to try and organize and possibly speed things up. I would emphasize that going through all the Object2D’s in a Dictionary is actually quite speedy and I would not be too concerned about using possibly more “optimal” solutions at an early stage of trying to understand Xojo canvases. To a human, it would seem unbelievably inefficient to redraw 20 items when you have just changed one of them. But for this task, Xojo is so efficient that I would not worry about it.

There is a concept in programming of “premature optimization”. First get the code to work with the easiest approach. Then decide if you want to optimize. With this particular issue, I suspect that you will find that redrawing “everything” with each Paint Event is so fast that it will not bother you.

[Anthony_G_Cyphers]

The code I posted is not optimal, nor is it prematurely optimized. It is, in my opinion, a solid base for the task that the user can easily build upon. I’m not saying your method is wrong, but – having done this a time or two – I know I’d probably end up rewriting the mechanism you outline at some future point. Whether that be out of necessity or OCD, it’s hard to say, but I know I’ve done it that way and eventually thought to myself “No. No, that has to go.”

[Yann_DUPONT]

@Anthony_G_Cyphers

NilObjectException

When using it I had a “NilObjectException” message.

[Yann_DUPONT]

@Robert_Livingston

To a human, it would seem unbelievably inefficient to redraw 20 items when you have just changed one of them

You absolutely read my mind

[Yann_DUPONT]

@Anthony_G_Cyphers

You need to instantiate the Dictionary before you try to use it, assuming your exception is a NilObjectException. That means, somewhere, you need:

MyDICTION = new Dictionary

Sorry but why do I have to instantiate MyDICTION which is a Property (MyDICTION as dictionnary) as when I use another property like mX as integer I can access it directly?

[Scott_C]

@Yann_DUPONT

Sorry but why do I have to instantiate MyDICTION which is a Property (MyDICTION as dictionnary) as when I use another property like mX as integer I can access it directly?

Because some datatypes like DateTime, Timer and Dictionary require instantiation.

Other datatypes like String, Integer, Double, Boolean, etc. are primitive datatypes, which do not.

Keep in mind, any kind of object (primitive & non-primitive) can be assigned as a datatype to a property, including custom Classes.

Regardless of whether a non-primitive object is assigned as a local variable or a property, it will almost always require the New keyword (instantiation). There a few exceptions, such as DateTime.Now & DateTime.FromString that come to mind.

[Tim_Parnell]

@Scott_C

There a few exceptions, such as DateTime.Now & DateTime.FromString that come to mind.

Those are functions. That’s why. The DateTime is instantiated inside the function for you.