When to use ':' versus '='?

treaves

I'm learning QML. I'm playing with an application that uses a ListView, and I'm using a delegate. In all of this QML, properties are set using a ':'.

I wanted to know how to do something when a delegate was tapped, and I found some code that does it. But in that code is the line

list_view1.currentIndex = index

My question is why in this case is '=' used instead of ':'? And more generally, when is each appropriate? I can't seem to find this in the documentation.

Thanks.

SGaist

Hi,

Because it's assigning index to currentIndex, it's not setting its property.

: is used when you set the properties when declaring the object. For the rest of the code, you can't do that.

JKSH

Hi,

@treaves said:

My question is why in this case is '=' used instead of ':'?

Because that is JavaScript code, and JavaScript only lets you assign values using '='.

And more generally, when is each appropriate?

':' has a few different uses in QML. In your case, ':' performs a property binding. In contrast, '=' performs an assignment.

See http://doc.qt.io/qt-5/qtqml-syntax-propertybinding.html for an explanation of property bindings.

treaves

Thank you both for your responses. I also appreciated the link; reading that helped a lot.

I'll brush up on JavaScript.