How to Implement Pull to Refresh in BlackBerry 10 Cascades

Sun 20 January 2013 by Xitij Ritesh Patel

Over the last little bit, I’ve been doing a lot of work on some apps for BlackBerry 10. With January 30th fast approaching, I was coding like a madman to try and meet the deadline, so I can get my hands on some awesome swag.

I was able to pump out two good quality apps relatively quickly by using the Tart project from the blackberry-py project. Thanks to Peter Hansen (@peter9477), we can write entire apps using just Python, QML, and JavaScript that perform at near-native speeds. This workflow allows you to rapidly prototype your app, far outweighing any concerns about performance when compared to C++.

One of the apps I built uses a UI paradigm called “Pull to Refresh.” If the user is viewing a stream of data, they can pull down on the list and reveal a hidden item that notifies them they can refresh the stream contents by releasing their touch. A number of people have asked me how to implement this.

Again, because of the speed of development that’s possible with BB Tart, I was able to put together a crude, but workable sample demonstrating how to implement this feature. Furthermore, I even integrated it with ADN’s global feed. I simply pulled a couple of libraries from Github and putting the building blocks together. I went from idea to functioning sample in 12 hours, with 6 hours of sleep in between.

As you can see, everything you need is in the blackberry-py-pulltorefresh GitHub repo. The app was built on top of my blackberry-py-bootstrap repo. I’d be more than willing to accept help/pull requests on the project to help improve it for all developers. The file you should look at in particular is PullToRefresh.qml.

You’ll note that I implemented a LayoutUpdateHandler to monitor changes in the item. If the Y-coordinate is equal to exactly 0, then it fires the refreshTriggered() signal. In my testing, this works relatively well since the control will snap to 0 when it is released past the threshold. However, it can sometimes be triggered while the user is still interacting with the control. Therefore, a better way would be to detect if the user is touching the control, and only firing if they’re not.

I hope that helps most of you BlackBerry 10 developers looking to implement this in your app. When I first got this working, I couldn’t stop playing with it! Hopefully this gives you the jumpstart you need. Oh and take a look through the rest of the repository, there’s some good stuff in there including a way to asynchronously load remote images.


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