Android

Room + ViewModel + LiveData + RecyclerView (MVVM) Part 5 – VIEWMODEL – Android Studio Tutorial



In part 5 of the Architecture Components tutorial, we will create our Viewmodel class.
The ViewModel works as a gateway between the UI controller and the repository. It stores and processes data for the activity/fragment and it doesn’t get destoyed on configuration changes, so it doesn’t lose it’s variable state for example when the device is rotated.
By extending AndroidViewModel, we get a handle to the application context, which we then use to instantiate our RoomDatabase.
In our activity we let the system provide us the correct ViewModel instance by calling ViewModelProviders.of, where we pass the Activity or Fragment this ViewModel’s lifecycle should be scoped to. When our Activity/Fragment is then destroyed, the ViewModel will go through it’s onCleared method and get removed from the memory.
In our activitie’s onCreate method, we retrieve the LiveData that is stored in our ViewModel and call observe on it, where we pass a LifecycleOwner and an Observer. In the onChange callback we get an update on our data whenever something in the corresponding database table changes. The LiveData will automatically start and stop sending updates to our activity at the right time in it’s lifecycle and clean up any unused references.

Watch the whole playlist:

Example code for this part:
https://gist.github.com/codinginflow/4d28adf5282a34a3bf8d945f5e1fa902

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Mourad ELGORMA

Fondateur de summarynetworks, passionné des nouvelles technologies et des métiers de Réseautique , Master en réseaux et système de télécommunications. ,j’ai affaire à Pascal, Delphi, Java, MATLAB, php …Connaissance du protocole TCP / IP, des applications Ethernet, des WLAN …Planification, installation et dépannage de problèmes de réseau informatique……Installez, configurez et dépannez les périphériques Cisco IOS. Surveillez les performances du réseau et isolez les défaillances du réseau. VLANs, protocoles de routage (RIPv2, EIGRP, OSPF.)…..Manipuler des systèmes embarqués (matériel et logiciel ex: Beaglebone Black)…Linux (Ubuntu, kali, serveur Mandriva Fedora, …). Microsoft (Windows, Windows Server 2003). ……Paquet tracer, GNS3, VMware Workstation, Virtual Box, Filezilla (client / serveur), EasyPhp, serveur Wamp,Le système de gestion WORDPRESS………Installation des caméras de surveillance ( technologie hikvision DVR………..). ,

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