Android app room database

How use local database in app

• make user experience more comfortable when your app cannot access to the internet. It also can persist data in your local machine.
• use annotation to create entity
  • @Entity for creating table and defining table name
  • @PrimaryKey define the primary key
  • @ColumnInfo define the column name in the table
• use @Dao to create query interface: data access object (DAO), which is used to communicate with local DB
  • Dao has provided some basic interface like update, insert, Query, etc.
• using @Database to create a new database or get a existing database

traditional Factory to generate viewModel

• add viewModel Factory to generate a params passing viewModel
• implement ViewModelProvider.Factory interface
• override create method
• usage
  • ViewModelProvider(this).get(ViewModel::class.java)
• tip
  • if error occur to you
    • Inheritance from an interface with ‘@JvmDefault’ members is only allowed with -Xjvm-default option
    • add the following section in app leve build.gradle

      android {
          ...
          kotlinOptions {
              ...
              freeCompilerArgs += [
                       "-Xjvm-default=all",
              ]
          }
      }

DI to generate viewModel

• add dependency in app level build.gradle

  • // hilt
    implementation "com.google.dagger:hilt-android:2.38.1"
    kapt "com.google.dagger:hilt-android-compiler:2.38.1"
    * add plugin in app level
      * ```id 'dagger.hilt.android.plugin'```
    * add dependency in project level
      * ```classpath "com.google.dagger:hilt-android-gradle-plugin:2.38.1"```
    * add hilt application entry
      ```kotlin
      @HiltAndroidApp
      class MainApplication: Application() {}
    
    

• add MainApplication to manifest
  *
  android:name="MainApplication"
• add annotation for viewModel injection @HiltViewModel
• add annotation @inject for being injected construct, filed, method, etc.
• add annotation AndroidEntryPoint in Fragment or Activity who needs to use DI data
• add dependency implementation 'androidx.fragment:fragment-ktx:1.5.0' in app level for view Model provider
  • val viewModel: SleepTrackerViewModel by viewModels()
• add custom DI module
  • using the @Module annotation to mark the class as a DI class
  • using the @InstallIn(SingletonComponent::class) to define provider life cycle
  • using @Provides to annotate the method is related to the specific module

coroutines in android

• what is it?
  • the way to handle long-running tasks elegantly and efficiently instead of callbacks
  • like callback to process task in asynchronous and non-block way
  • use suspend keyword for making asynchronous code in sequential way
  • architecture
    • Job: using for operating coroutine
    • Dispatcher: make coroutines run in different threads
    • Scope: define which context the coroutines runs
  • why coroutines is safe and how?
• How to use it?
  • add suspend in the front of a function signature in Dao
  • add coroutine dependency in app level build.gradle
    • implementation “androidx.lifecycle:lifecycle-viewmodel-ktx:2.2.0”
    • implementation “androidx.room:room-ktx:$room_version”
  • define MutableLiveData variable and init it by viewModeScope.launch starting a coroutine in current viewModel
• Using it for long-running database

Room database