Really ?

This is so annoying. I have no bluetooth mouse powered on but I do have a USB one and it works fine. And the mouse control panel says it cannot find it so I cannot change the tracking speed. System Report knows there’s a mouse connected as you can see.

Turn the bluetooth mouse on and the panel finds that and now I can adjust the tracking speed. But it doesn’t affect the USB mouse – which is still connected and working (the bluetooth mouse is literally upside down on my desk untouched)

No. I don’t want a wireless mouse as I’m tired of my Magic mouse and “LOST CONNECTION”. Apparently Apple insists I use a wireless mouse,

Awesome !

= vs IS

A good question on the discord server I participate in prompted a good question. It started with IS and = are just synonyms right?

It turns out that MOST times this may be true. But not always. And that little “but not always” can get you in trouble if you dont know when the difference is important.

IS is always used to determined if one instance of a class refers to the exact same instance as another reference. You might want to reread my prior post about classes, instances and objects

And in many cases, but not all, = will give you the same result as using IS.

So code like

Dim d1 As New Class2
Dim d2 As New Class2

If d1 = d2 Then
  System.debuglog "d1 = d2 => true !"
Else
  System.debuglog "d1 = d2 => FALSE !"
End If

If d1 Is d2 Then
  System.debuglog "d1 IS d2 => true !"
Else
  System.debuglog "d1 IS d2 => FAlSE !"
End If

will usually put out debug log messages that say D1 = D2 => false from both checks.

This assumes that our class, Class2, does NOT implement operator_compare. And that is the caveat here. IF a class implements operator_compare the IS and = operators may not give the same result any longer.

Operator_compare is often used to compare the contents of a class – and not the references (although it doesnt have to compare contents since you can make it do whatever you want).

If we defined our class, Class2, like

Protected Class Class2
  Sub Constructor(contents as string)
    myContent = contents
  End Sub

  Function Operator_Compare(rhs as Class1) As integer
      If rhs Is Nil Then 
        Return -1
      End If
		  
      If Self.myContent < rhs.myContent Then
        Return -1
      End If
      If Self.myContent > rhs.myContent Then
        Return 1
      End If
		  
    Return 0
		  
  End Function

  Private myContent As String
End Class

Now our code above will give very different results because Operator_compare is used when the line

If d1 = d2 Then

is run. In this case it will call the custom operator_compare method and that compares the contents of two objects and NOT whether or not two objects references refer to the same object. However, the line

If d1 Is d2 Then

will ALWAYS determine if the two objects references refer to the same instance.

And now you know !

WAY off topic but so what ????

It is my blog and this is something I’ve been working at for months.

I PASSED my on snow certifications for the Canadian Ski Patrol and now get to do a few shifts working with more senior patrollers before they turn me loose and I can patrol on my own !

What an awesome way to spend New Years Day !!!!!!

And I would like to take the time to thank ALL of the instructors that have helped all of the candidates along. They have been really really great !

WeakRef usage

There was a good question from Markus in a recent comment on a different post of mine.

In children of a window we should keep track of the parent window by using WeakRef.
But what if I have a class cDepartment with a list of employees defined as Employees() as cEmployee – should that then better also be defined as WeakRef? And why or why not?

First I’ll say “it depends” as there’s certainly no single correct answer to such a question. In many cases it will depend on the expected usage.

WeakRefs are a curious thing. In Xojo most times you have a reference to an object its a strong reference. What happens is that the objects reference count is increased and only when that counter gets set to 0 will the object be destroyed.

For instance, if we have code like the following

Class Foo

  Sub Destructor()
    break
  End Sub

End Class


dim firstRef as Foo
dim secondRef as Foo

firstRef = new Foo 
// the object firstRef refers to now has a reference count of 1

secondRef = firstRef 
// since secondRef refers to the SAME object as firstRef
// the object firstRef refers to now has a reference count of 2

firstRef = nil
// the object firstRef refers to now has a reference count of 1

secondRef = nil
// the object firstRef refers to now has a reference count of 0
// and it will be destroyed and the breakpoint in the destructor
// will be encountered

Now what happens if we use a WeakRef instead for secondRef ? If we turn that code into the following

Class Foo

  Sub Destructor()
    break
  End Sub

End Class


Dim firstRef As Foo
dim secondRef as Foo
Dim weakSecondRef As WeakRef // <<<<<<< note the type !

firstRef = New Foo 
// the object firstRef refers to now has a reference count of 1

weakSecondRef = New WeakRef(firstRef)
// since weakSecondRef is a WeakRef the object 
// firstRef refers does NOT increment its reference count

firstRef = Nil
// the object firstRef refers to now has a reference count of 0
// and it will be destroyed and the breakpoint in the destructor
// will be encountered now

// but what about weakSecondRef's contents ???
// lets fetch that value and see whats in there now
secondRef = Foo(weakSecondRef.Value)

break // <<< here you will find that the returned value is NIL !

And if you try to use the object contained by the weakref secondRef you will find that it is nil. A weakref allows an object to be referenced in a way that it does not increment the original objects reference count which CAN let that object be nil’d in other code.

When you use a weakref you MUST check the VALUE of the weakref to see if what you get back is NIL because the object may have been set to nil elsewhere.

Now that we have the basics of weakrefs out of the way lets turn back to Markus’ original and my original reply of “it depends”.

n children of a window we should keep track of the parent window by using WeakRef.

Indeed you may want to have child windows retain a weakref to refer to a parent window. It would allow you to close the parent and not the child, as the weakref will not increment the reference count of the parent window. But, you may want the parent to not be set to nil when there are child windows.

This decision will depend entirely on how your UI is supposed to work. If those child windows should not exist without a parent then a hard reference to the parent may make perfect sense.

But what if I have a class cDepartment with a list of employees defined as Employees() as cEmployee – should that then better also be defined as WeakRef? And why or why not?

Again this will depend entirely on how the cDepartment class should behave. Can cEmployees be added & removed at runtime and should the cDepartment class be able to deal with this ? Or should cDepartment need to be reconstituted when such changes of its employees are made ? The correct behaviour isnt dictated by the underlying code and whether you should use weakrefs but by the needs of the application and how cDepartment should behave.

You could always use weakrefs but this could have unintended consequences for the cDepartment class as this would allows its cEmployees to be removed at runtime. If you had used a FOR EACH loop with an iterator to perform some function you would need to handle the exceptions that could be encountered. Iterators will be invalidated by removal of an employee while iterating over the list and will raise an exception of this occurs. Weakrefs would permit this. Hard references would not.

2019, The Lost Year, in review

2019 has been an interesting year to say the least.

Mine started off with the septic system needing to be replaced in the first week of January as the old system had been installed in a manner that it was not repairable and it had failed. So in the cold of January our yard was torn up and excavation work went on. One of our basement bedrooms had to have its floor cracked open and a new main line to the septic system installed. $25K later it was all back in working order and we just had landscaping to fix up.

Awesome start !

Work on Xojo 2019r1 was progressing when I was suddenly let go in March.

I panicked a bit. But things have worked out well for me so far and I’m happy doing what I’m doing for a really great group of clients. Since then I’ve created 300+ Feedback reports.

Xojo 2019r1 was released in April and thats the last release that I really contributed much to. 2019r1.1 went out in May.

Betas for Xojo 2019r2 started shortly after that and this brought API 2.0 and a fair number of bugs and complaints along with it. Especially aggravating were changes to many property names, method names and event names. Event names proved to be the most difficult for developers of all sorts, especially in the third party arena, to deal with. For my uses it was a beta that was going along fine until API 2.0 hit then it made it clear that my clients projects were NOT going to transition easily so I more or less stopped testing entirely.

Xojo 2019r2 was released in Oct. There was more angst expressed about the renames by users that were not part of the beta program.

About this time I started taking training to be a Ski Patroller. I’d thought about going and getting certified as a ski instructor again but Ski Patrol made more sense.

2019r2.1 with a number of bugs fixes followed in Nov. Of significant note 2019r2 was pulled from further distribution and 2.1 reverted the changes to event names. This was a welcome reversion. I think a number of people were surprised that Xojo took this course of action. I really didnt test much in this release.

Shortly after, in Dec, 2019r3 was shipped and it brought iOS dark mode along with it and a handful of other fixes that were not iOS related. Again since it did not contain a lot of fixes that were really relevant to my clients I mostly didnt test it and have only lightly used it.

And about this time I passed my written and diagnostic exams to progress on to the on snow training to be a Certified Canadian Ski Patroller. (YAY !!!!!!)

For some the year was a non-event as far as Xojo went. No new OOP features, classes, controls or other significant improvements were added. A lot of changes were made. But Xojo hasn’t become more stable, capable, or reliable as a result of those changes. Just different. It’s about the same as it always has been and several new bugs seemed to be a result of API 2.0 changes. While API 2.0 is out now it isn’t a game changer in most respects. At least not yet. It’s hard to know what else might come along in the future but the roadmap doesnt seem to have anything for API 2.0 further out beyond expanding to iOS. What remains is still things that have been on the to do list for several years like Web 2.0, Android, and plugins written in Xojo.

For me both personally and professionally it was a year with big changes in my personal life and professional life. For Xojo not so much.

How was your year ?

#if Targetxxxx

I’ve seen this a lot in posts on the forums and even in code submitted as part of bug reports

If TargetWindows Then
  // Windows only code not excluded from compilation.
End If

The code inside the if will only execute on Windows. However becuase this code is just a normal if it HAS to COMPILE on ALL targets even if the intention is that it only be used on Windows (which it obviously is)

If you intend some code to ONLY be used on Windows you’re better off to use this form

#If TargetWindows Then
  // Declares for example
#Endif

This code will ONLY exist in a Windows builds and so can ONLY execute on Windows. And, because it will only be used on Windows the compiler will ignore the code inside the #if … #endif on all other platforms so the code doesn’t even have to compile on macOS or Linux (which it would in the first example shown)

Usually when you see the first form you really want the second using #if

Next time you find yourself writing

if Target

reconsider if you really should be using #if instead

Classes, Instances and Objects

There’s a fun “theoretical question” on the forums.

What is the relationship between a class, object, and instance?

Lets see if I can help any (or maybe just confuse the heck out of folks even more)

In Xojo in the IDE when you define a CLASS you are creating a “template” for how every item of this type will behave. You’re defining the properties, the methods, events etc etc etc. And EVERY item that IsA <this type I defined> returns true for IsA one of these.

AT runtime when you application runs and it uses the NEW operator to create a new item of this type you are creating new INSTANCES. Instances are the ACTUAL copies you create that you can manipulate at runtime.

And EVERY instance in Xojo IsA Object. Its the base object for EVERY dynamically created type where you use NEW to create one.

So CLASSES are a design time thing.

INSTANCES and OBJECTS are runtime things.

Silent readership

I’m curious about something. Actually I’m curious about a LOT of things; just ask my Canadian Skip Patrol instructors 😛
But I’m REALLY curious about one thing when it comes to this blog.

I can see there are a decent number of readers & views thanks to the stats that WordPress gives me. But, there’s very few comments.

I’m really curious why people don’t comment. Do the same things that make it so you don’t comment here also apply to other venues like the Xojo forums ? The reason I ask is that, as anyone who knows me well can vouch for, when I have something to say I say it. And if I have a strong opinion about something its nearly impossible to get me to shut up. Again you can ask anyone who knows me well – and if it’s Bob’s Keeney reading this I’m 100 sure he’s just shaking his head going “Yup!”

Even just a “Hey thanks I read that post and it was informative” is great feedback to get. Or “Hey I found a typo”. And yeah you can tell me I’m being dumb if I post something dumb 🙂

So what is it that keeps you from commenting ? And yes I get the irony of asking people who don’t comment on other posts to comment on this one 🙂

Performance tweaks

In Xojo there are a number of things you can do to improve the performance of your code.

There are various pragmas you can enable that can improve speed – I’d suggest only doing this once you code is fully debugged and known to be working properly as turning these checks of can mean IF you have a bug your application just crashes hard.

And there are other things you can do like lifting out code that repeatedly does lookups in arrays.

So instead of

dim something(1000) as String

// intervening code to load data into the array

for i as integer = 0 to something.ubound

   if something(i) = "abc" then
   elseif something(i) = "def" then
   elseif something(i) = "ghi" then
   end if
next

you might rewrite this as

dim something(1000) as String

// intervening code to load data into the array

// 1) eliminate repeatedly accessing the Ubound property
dim maximumIndex as integer = something.ubound 

for i as integer = 0 to maximumIndex

   // 2) eliminate repeatedly doing an array access
   dim thisItem as string = something(i)

   if thisItem = "abc" then
   elseif thisItem = "def" then
   elseif thisItem = "ghi" then
   end if

next

It would be nice if the compiler could/would do more optimization of code. There are a host of optimizations that you could apply manually like common subexpression elimination and loop invariant code motion.

But sometimes the biggest performance wins are not from tweaks like these. Often applying a different algorithm has a much bigger bang for the buck than anything.

When I worked at Xojo there were a couple areas where simply by inverting how some data was accessed in memory the entire process was sped up enormously.

Databases will do this and may use the MOST selective index to retrieve data first so the initial set of data is very tiny, instead of starting with the most broad set of data, and then winnowing it down further. By doing this they can decrease the amount of memory required and the amount of data to iterate though to satisfy whatever query you’ve executed.

When you have a performance issue I would START by reconsidering how the data is accessed and used and whether you can alter the algorithm to gain an initial big speed up by doing things in a different order.

And once you get the algorithm working the way you want then apply all the other tweaks to code to squeeze the most out of it.

And JUST to be clear make sure you do timings in a COMPILED and BUILT version NOT aa debug version using RUN as a debug version still has a lot of debug related code in it that can influence the results and MAY mislead you.