added draggable property to ScrollView, closes #2260

[codeshaunted]

Adds a draggable property to ScrollView that binds to the interactive property of the internal Flickable. Should close #2260.

[CLAassistant]

All committers have signed the CLA.

[ogoffart]

Thanks a lot for the PR!

This is a nice improvement and the code looks good.

I’m not sure if draggable is the best name. Maybe something like mouse-drag or enable-mouse-pan would be clearer. The reason is that in the future, we want ScrollView to always support dragging with a finger (touch), even if this property is false. But to do that, we first need support for detecting if the input is from a mouse or a finger (see #4352).

Right now, this property is only about dragging with the mouse, so the name should make that clear.

Also, we should keep the default behavior in the Material style, to dragging is enabled by default on android. It would be good to mention in the docs that the default can depend on the style.

What do you think?

[ogoffart]

This defaults to false because on android we should default to draggable.

[codeshaunted]

I'm a bit confused, wouldn't I want interactive: true; to default to draggable? And, does this also apply for Cupertino?

[ogoffart]

right sorry my comment was not clear.
It currently defaults to true for the material style (as opposed to all the other style which explicitly set interactive: false

The material style is different because this is a style which is primarily interacted with touch because of android.
While the other style are to be used on desktop.

It is true that cupertino is currently the default on iOS, but our iOS support is not finished yet.

[codeshaunted]

I've renamed the property to mouse-drag to hint that it's only for the mouse. I've also removed the setting to false for Material style, and added a note in the docs about this. I'm not sure if this is the best way to denote it in the docs, so please let me know if there's a better way. Thanks for the input!