Kitts wrote:
Hi all,
I have been doing some coding and using the property manager in flightgear
but i want to know what is the right way to do it.
I use the method "fgGetNode("/path/to/property", true)" to get an existing
property or create one if not there. There are a few things i want to know
that i list below:
1) A node that is used in the flight system also results in the method
"isTied" failing and the It does allow me to tie this already existing
property to a variable?!? Is this the expected behavior? Isn't the property
supposed to be tied to a variable somewhere already?
No, properties are not stored by default in the program 'variables',
that's why they are not tied.
In practice however there is a lot of properties wich have some get/set
code associated with
them, and very few wich are directly tied to a variable.
2) When a property did not previously exist, is it necessary to create a
variable and tie the node to that variable? I find the system to be working
either ways. If i do not tie it, the property is displayed as "double" in
the property browser else it displays the data type that it has been tied
to.
If it's tied to a variable then the property will allways be of the
right type. Else it will has the type
you gave it when you created it / accessed it the first time. Even if
you write something in another
type it will keep it's creation type. The props functions are doing all
the casting for you.
3) When the property has been explicitly tied, no matter what the value is
initialized to using the "setDoubleValue" method the property browser shows
the value as zero. This display of zero does not happen when the property
is not tied explicitly.
Perhaps are you overwriting the value in your code (and why would you
use setdoublevalue in your
own code when you can directly write in the container variable ?). Look
at the AIBase class,
they use tied properties and you can check the values in the property
browser. Btw, for properties tied
or having a setter function, the property browser *won't* update the
value displayed when the
property change. You must close/open the property browser to see the change.
4) I would also like to add a change listener to the class that i have
written so that the class is informed as and when a variable being watched
has changed value. I believe the way to do this is to use the
"SGPropertyChangeListener" class as a base class and implement the
"valueChanged" method to do the job. Is this correct?
I think, never done it myself. Note that if you own the property you can
also use a set function
to update its value, and then you allways know when the property has
changed.
So now, back to my question. What is the right way to use the property
manager? Which are the right methods that are to be used and in what
sequence?
If you own the property and you manage it I think the usual way is to
use the C++ style, ie you use a get and a set function to access the
member, so you can use fgTie(propertyname, this, get_function,
set_function).
If it's not your property then you use fgGetXXX.
Harald.
_______________________________________________
Flightgear-devel mailing list
Flightgear-devel@flightgear.org
http://mail.flightgear.org/mailman/listinfo/flightgear-devel
2f585eeea02e2c79d7b1d8c4963bae2d
