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Monthly Archives: July 2016

A few days ago, an interesting idea came up in the PebbleDev Slack channel: could a library make it easier for Pebble developers to integrate their apps with Android APIs, but save the pain of each and every one of them needing to publish an app with PebbleKit Android? This would be similar to how Dashboard operates, but by sharing the API access to other apps that are installed.

Turns out, it can! In one of my signature coding bursts I set to work, and prototyped a system that did just this. The result is the Dash API. With it, you can finally (and easily) provide one of the most common watchface widget requests – things like the phone’s battery level, or connectivity status.

How does it work?

The Dash API (named after Dashboard) Pebble package uses AppMessage to send requests to read data (such as WiFi network name, or phone battery level), or write to an API (such as turning off WiFi). Using a unique key to recognise Dash API messages, the Android app can respond to these by reading the data or manipulating the Android API and returning a response code. All the developer needs to do is instruct their users to install my Dash API Android app, and then their app (and any others that use the Dash API) can take advantage of the APIs presented through the library. This approach makes the Dash API an install once, use in many apps service.

The upshot of all this is that a C developer making a watchface that wants to show the phone battery level (such as the demo app Dual Gauge) need only use the Pebble package and not write a single line of Java, let alone go to the trouble of publishing an Android app on Google Play.

But how can one companion app target them all, without knowing they exist?

Luckily, you can extract the UUID of an app that sends an AppMessage packet to the phone from the Intent object broadcast from the Pebble Android app. Most (hopefully app) companion apps that manually register a BroadcastReceiver do a ‘good citizen’ UUID check to make sure they only respond to messages from their corresponding watchapp. This data can be used to simply redirect an incoming message’s result right back at it, without the need to create a PebbleKit Android app with baked in UUID for each individual app.

So how can I use it?

Simple. As explained in the GitHub README.md file, a C developer should first install the package:


$ pebble package install pebble-dash-api

Next, include the single library file and call the initialiser when your app is starting, supplying the app’s name (for presentation in the Android app) and an error callback for receiving any errors that may occur:

#include <pebble-dash-api/pebble-dash-api.h>;
#include <pebble-events/pebble-events.h>

#define APP_NAME "My App"

static void error_callback(ErrorCode code) {
  // Receive error codes here
}

static void init() {
  dash_api_init(APP_NAME, error_callback);
  events_app_message_open();

  /* Other init code */
}

Next, check the Android app is available and up to date:

dash_api_check_is_available();

The result will be passed to your error_callback. Once you get ErrorCodeSuccess, it is safe to start making queries, such as getting the battery level, etc. Code examples are included in the GitHub README.md file.

What else do I need to know?

As of 1.1 (released today), apps that read data and API states can do so invisibly. However, apps that wish to write to an API (such as turning off WiFi) will cause a notification to appear that will prompt the user to grant it access within the Dash API app. Once this is done, operation will continue without further intervention, unless permission is revoked. This should hopefully prevent any rogue apps messing with the phone, and give users visibility into which Pebble apps they have used are using the Dash API.

Links

GitHub Repo

Dash API Android app (direct your users here!)

NPM Package

Example App (Dual Gauge)

What’s next?

In the future, I’d like to expand the capabilities offered by the Dash API to other popular widget requests, things such as unread SMS count and next Calendar appointment. Perhaps for another day – coordinating GitHub repos, NPM packages, Android apps, and Pebble apps is quite tiring!

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That’s right, the latest and greatest update to Dashboard is now live (pending Google Play deployment delay). The new features are (in descending order of number of requests received):

  • A choice of Find Phone sound from system notification sounds. While these are guaranteed to be available, free-form choice of file proved too tricky to handle (see Android file manage content:// URI problems discussed elsewhere).
  • An option to post an Android notification (and by extension, to the watch) when the phone has fully charged (see details below). This approach is better than the original one planned which involved custom UI in the watchapp, but would rely on an assumption about how long PebbleKit Android would take to launch the watchapp before messaging it.
  • Holding down the button now uses repeat button clicks to reduce wear on the Pebble buttons while scrolling through toggles.
  • Since I’m making bigger use of Notifications, installed a proper white notification icon to improve upon the old ‘white circle’.
  • More misc UI improvements in both app components, including a donation link for those inclined, after some minor success in News Headlines.

So how does the new ‘full charge notification’ feature work? I’m glad you asked!

The Short Answer

Once your phone has reached 100% charge (when it was previously 99% or less), an Android notification is posted, which is displayed on Pebble (for free!) unless for some reason Dashboard was disabled in the Pebble app.

The Long Answer

Oh boy, this was a tricky one. While the ACTION_BATTERY_CHANGED Intent is available for apps to know when the battery level changes, it’s a special case that cannot be simply registered in AndroidManifest.xml for spin-up whenever required. It has to be programmatically registered. For an app designed to run with extremely minimal interaction with the Android app component, this is tricky.

So what have I done? When the user toggles the feature on in the Android app, the BroadcastReceiver for the above Intent is registered. Sounds simple, right? Well that works for anywhere between ten minutes and an hour or so. I was charging my phone from 99% in testing, and seeing the notification after a few minutes as expected, but a frustrating lack of notification after leaving the phone idle for couple of hours on longer charges.

For reasons unknown to me, the system kills my programmatically registered BroadcastReceiver at seemingly random intervals. Remember, this wouldn’t happen with a nice and convenient receiver registered in AndroidManifest.xml.

Undeterred by this (because this is a nice feature idea), I found another solution. I made the receiver object a static class member, and used the Android AlarmManager to check it was not null at infrequent intervals (currently half an hour). This seemed to work well, once I realised by trial and error that Android Studio appears to kill BroadcastReceivers and AlarmManager alarms, but not deliver the ACTION_PACKAGE_CHANGED which I use to restore the alarms after a theoretical future app update is installed.

In addition, new users would not have their ‘keep alive’ alarms registered upon first install, since ACTION_PACKAGE_ADDED is not delivered to the app that has just installed (why!?). Fancy another complication? Here you go: AlarmManager alarms are all killed when the device is rebooted, so I make additional use of ACTION_BOOT_COMPLETED to restore them.

Finally

So there we go! I’ve always been a vocal proponent of Android’s Intent system for IPC, but after this set of complications (which has still yielded an apparently solid solution), I’m not so sure. Ah, who am I kidding? Still a big fan!

Dashboard can be installed from the Pebble appstore and the Google Play Store.