Error monitoring
In Fabulous, everything happens in a centralized message loop that is responsible for calling your init
, update
and view
functions.
Fabulous allows you to plug into this loop to run custom logic such as logging and error handling.
There’s a few built-in functions available already:
F#To use them, you will need to add them when declaring the runner. You can add multiple trace functions, one after another.
In this example, logs will be written to the console before the error handler can write the exceptions to the disk.
Writing a custom trace function
Writing a custom trace function is simple.
You need to make a function that accepts a Program<'args, 'model, 'msg, 'view>
and that outputs another Program<'args, 'model, 'msg, 'view>
.
This Program
defines the handlers that are responsibles for calling init
, update
and views
as well as handle errors. You can define your own handlers instead to do additional logic.
Make sure to call the previous Program
handlers in your owns, otherwise you will completely bypass Fabulous.
Here’s a simple example that prints a message each time something happens
You’re not required to implement all handlers, if you only need to override update
then just override that one.
AppCenter
Here’s a good example of implementing our own trace function.
Visual Studio App Center is a DevOps portal tailored for mobile application development. It handles everything from build, tests, distribution, analytics and crashes reporting, for Android, iOS and UWP.
We can define our own trace functions to send analytics and crashes to AppCenter.
AppCenter provides us with a really simple way to report to it. We only need to install the following packages:
Once the packages added, we can access 3 methods:
Start
: Initialize AppCenter by providing our app secretsAnalytics.TrackEvent
: Track a custom event with associated dataCrashes.TrackError
: Track an exception.
AppCenter will provide a dashboard of those events and exceptions along with stack traces
Here we override update
to call Analytics.TrackEvent
, and onError
to call Crashes.TrackError
.
We could trace everything, but you should consider to trace the minimum to protect your users' privacy.
To do that, we have added a AppCenterUpdateTracer
function that will filter the messages that interest us and what data we should extract from it.
In our App
class, we need to call AppCenter.Start("appsecrets", typeof<Analytics>, typeof<Crashes>)
to initialize it.
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