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Darko Martinović edited this page Jan 15, 2020 · 2 revisions

EventLiveData

This is extension of LiveData that allows propagation of events that are consumed only once to multiple observers.

Communication

Find me here :

Binaries

implementation 'com.rugovit.eventlivedata:eventlivedata:1.0'
  • EventLiveData: Download

Sample usage

A sample project which provides runnable code examples that demonstrate uses of EventLiveData is available in the EventLiveData/app/ folder of this repository.

Basic usage

In it's basic use case EventLiveDate is observed in a same manner as regular LiveData

MutableEventLiveData<String>  eventLiveData =new MutableEventLiveData<>();
    // ...
    //Fragment 1
viewModel.event.observe(this, Observer {
    // ...
})
    //Fragment 2
viewModel.event.observe(this, Observer {
    // ...
})

onStart

In case where you are observing LiveData in fragment that that is on backstack there is common error where upon going back to previous fragment you add new observer on a same LiveData. That is because fragment never reaches DESTROYED state therefore observer is never released. Calling observeInOnStart() method instead of observe() in onStart() fragments or Activity's method you are ensuring that when fragment or activity reaches STOPED state your observer is released.

   //...

    @Override
    public void onStart() {
    
        eventLiveData().observeInOnStart(this, o -> {
            //..
        });
    
    }

    //...

Custom observer lifecycle limitation

When you need to limit your observer lifecycle range from when it will receive events to when it will be released from EventLiveData, use observe( LifecycleOwner, Observer ,State,Event) method.

    //..

    eventLiveData().observe(this,o->{
            //..
            }, Lifecycle.State.RESUMED, Lifecycle.Event.ON_STOP);
    
    //..

It might create unexpected behaviors so use only if you are familiar with Android components lifecycle. Lifecycle State change happens after lifecycle Event so you need to keep that in mind when setting this method. For example if you observe your EventLiveData with this lifecycle range:

    eventLiveData().observe(this,o->{
            //..
            }, Lifecycle.State.STARTED, Lifecycle.Event.ON_RESUME); // observer will not receive any events!!!

Observer will not receive any events. That is because STARTED state will change right before ON_RESUME is triggered, leaving no time for your observer to react to possible events.

Bugs and Feedback

For bugs, feature requests, and discussion please use GitHub Issues.

LICENSE

Copyright 2015 The RxAndroid authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
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