# Property bindings in more detail

**URL:** <https://forum.inductiveautomation.com/t/property-bindings-in-more-detail/15370>\
**Category:** Ignition\
**Created:** [September 15, 2017, 7:59pm UTC](https://forum.inductiveautomation.com/t/property-bindings-in-more-detail/15370 "2017-09-15T19:59:35Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![iamthebull](https://avatars.discourse-cdn.com/v4/letter/i/58f4c7/32.png) [@iamthebull](https://forum.inductiveautomation.com/u/iamthebull)\
**Post date:** [September 15, 2017, 7:59pm UTC](https://forum.inductiveautomation.com/t/property-bindings-in-more-detail/15370/1 "2017-09-15T19:59:35Z")

</div>

I’m trying to understand property bindings in more detail. In particular I’m curious about the evaluation of property bindings on a component in a window when the window is first opened (not cached). Obviously each bound property will be evaluated in turn. But what if one particular property depends on another and that other property has not yet been evaluated?

I did a test. On a template I defined two properties - `aName` and `smName`. In a window I placed an instance of the template and I bound the value of `aName` to the value of `smName` using a property binding. I set the value of `smName` to `'sm1'`. In the propertyChange event script of the template I have the following:

```auto
if event.propertyName == 'aName':
	print 'aName changed', event.newValue, event.oldValue if event.oldValue else 'None'
if event.propertyName == 'smName':
	print 'smName changed', event.newValue, event.oldValue if event.oldValue else 'None'

```

When the window is opened the output on the console is:

```auto
aName changed sm1 None
smName changed sm1 None

```

This leads me to believe that `aName` is evaluated before `smName`. But when `aName` is evaluated `smName` has no value (you can see it changed from `None` to `sm1` but not until after `aName` was evaluated). So how does `aName` get the value `sm1`? Should it not get the value `None`?

On a side note: when does the component get painted on the window? After all these bindings have been evaluated?