app: setup pagination and a viewmodel for posts

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

app/build.gradle

@@ -50,11 +50,13 @@ tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {
 
 dependencies {
 
-    kapt "com.google.dagger:hilt-android-compiler:$hilt_version"
+    kapt "com.google.dagger:hilt-android-compiler:$hilt_dagger_version"
+    kapt "androidx.hilt:hilt-compiler:$hilt_androidx_version"
     implementation(project(":data"))
     implementation(project(":lobsters-api"))
     implementation(project(":model"))
     implementation 'androidx.core:core-ktx:1.5.0-alpha03'
+    implementation 'androidx.activity:activity-ktx:1.2.0-alpha08'
     implementation 'androidx.appcompat:appcompat:1.3.0-alpha02'
     implementation "androidx.compose.foundation:foundation:$compose_version"
     implementation "androidx.compose.foundation:foundation-layout:$compose_version"
@@ -66,12 +68,14 @@ dependencies {
     implementation "androidx.compose.ui:ui-text:$compose_version"
     implementation "androidx.compose.ui:ui-text-android:$compose_version"
     implementation "androidx.compose.ui:ui-unit:$compose_version"
+    implementation "androidx.hilt:hilt-lifecycle-viewmodel:$hilt_androidx_version"
     implementation "androidx.lifecycle:lifecycle-runtime-ktx:$lifecycle_version"
     implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version"
     implementation "androidx.ui:ui-tooling:$compose_version"
     implementation 'com.google.android.material:material:1.3.0-alpha02'
-    implementation "com.google.dagger:hilt-android:$hilt_version"
-    androidTestImplementation "com.google.dagger:hilt-android-testing:$hilt_version"
+    implementation "com.google.dagger:hilt-android:$hilt_dagger_version"
+    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$coroutines_version"
+    androidTestImplementation "com.google.dagger:hilt-android-testing:$hilt_dagger_version"
     testImplementation 'junit:junit:4.13'
     androidTestImplementation "androidx.ui:ui-test:$compose_version"
     coreLibraryDesugaring "com.android.tools:desugar_jdk_libs:1.0.10"

app/src/main/java/dev/msfjarvis/lobsters/MainActivity.kt

@@ -1,47 +1,42 @@
 package dev.msfjarvis.lobsters
 
 import android.os.Bundle
+import androidx.activity.viewModels
 import androidx.appcompat.app.AppCompatActivity
 import androidx.compose.foundation.Text
-import androidx.compose.foundation.lazy.LazyColumnFor
+import androidx.compose.foundation.lazy.LazyColumnForIndexed
 import androidx.compose.material.Scaffold
 import androidx.compose.material.TopAppBar
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.Providers
 import androidx.compose.runtime.ambientOf
-import androidx.compose.runtime.mutableStateListOf
+import androidx.compose.runtime.collectAsState
 import androidx.compose.ui.platform.setContent
 import androidx.compose.ui.res.stringResource
-import androidx.lifecycle.lifecycleScope
 import dagger.hilt.android.AndroidEntryPoint
 import dev.msfjarvis.lobsters.api.LobstersApi
-import dev.msfjarvis.lobsters.model.LobstersPost
+import dev.msfjarvis.lobsters.data.LobstersViewModel
 import dev.msfjarvis.lobsters.ui.LobstersItem
 import dev.msfjarvis.lobsters.ui.LobstersTheme
 import dev.msfjarvis.lobsters.urllauncher.UrlLauncher
-import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.withContext
+import kotlinx.coroutines.ExperimentalCoroutinesApi
 import javax.inject.Inject
 
 val UrlLauncherAmbient = ambientOf<UrlLauncher> { error("Needs to be provided") }
 
 @AndroidEntryPoint
+@ExperimentalCoroutinesApi
 class MainActivity : AppCompatActivity() {
   @Inject lateinit var urlLauncher: UrlLauncher
   @Inject lateinit var apiClient: LobstersApi
+  private val viewModel: LobstersViewModel by viewModels()
 
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     setContent {
       Providers(UrlLauncherAmbient provides urlLauncher) {
         LobstersTheme {
-          val posts = mutableStateListOf<LobstersPost>()
-          lifecycleScope.launchWhenCreated {
-            withContext(Dispatchers.IO) {
-              posts.addAll(apiClient.getHottestPosts(1))
-            }
-          }
-          LobstersApp(posts)
+          LobstersApp(viewModel)
         }
       }
     }
@@ -49,15 +44,21 @@ class MainActivity : AppCompatActivity() {
 }
 
 @Composable
+@ExperimentalCoroutinesApi
 fun LobstersApp(
-  items: List<LobstersPost>,
+  viewModel: LobstersViewModel
 ) {
   val urlLauncher = UrlLauncherAmbient.current
+  val state = viewModel.posts.collectAsState()
+  val lastIndex = state.value.lastIndex
 
   Scaffold(
     topBar = { TopAppBar({ Text(text = stringResource(R.string.app_name)) }) },
     bodyContent = {
-      LazyColumnFor(items) { item ->
+      LazyColumnForIndexed(state.value) { index, item ->
+        if (lastIndex == index) {
+          viewModel.getMorePosts()
+        }
         LobstersItem(item) { post ->
           urlLauncher.launch(post.url)
         }

app/src/main/java/dev/msfjarvis/lobsters/data/LobstersViewModel.kt

@@ -0,0 +1,32 @@
+package dev.msfjarvis.lobsters.data
+
+import androidx.hilt.lifecycle.ViewModelInject
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import dev.msfjarvis.lobsters.api.LobstersApi
+import dev.msfjarvis.lobsters.model.LobstersPost
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.launch
+
+
+@ExperimentalCoroutinesApi
+class LobstersViewModel @ViewModelInject constructor(
+  private val lobstersApi: LobstersApi,
+) : ViewModel() {
+  private var apiPage = 1
+  private val _posts = MutableStateFlow<List<LobstersPost>>(emptyList())
+  val posts: StateFlow<List<LobstersPost>> get() = _posts
+
+  init {
+    getMorePosts()
+  }
+
+  fun getMorePosts() {
+    viewModelScope.launch {
+      _posts.value += lobstersApi.getHottestPosts(apiPage)
+      apiPage += 1
+    }
+  }
+}

build.gradle

@@ -4,7 +4,8 @@ buildscript {
         compose_version = '1.0.0-alpha03'
         coroutines_version = '1.3.9'
         dagger_version = '2.29.1'
-        hilt_version = '2.29-alpha'
+        hilt_androidx_version = '1.0.0-alpha02'
+        hilt_dagger_version = '2.29-alpha'
         kotlin_version = '1.4.10'
         lifecycle_version = '2.3.0-alpha07'
         moshi_version = '1.9.3'
@@ -17,7 +18,7 @@ buildscript {
     dependencies {
         classpath "com.android.tools.build:gradle:4.2.0-alpha12"
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
-        classpath "com.google.dagger:hilt-android-gradle-plugin:$hilt_version"
+        classpath "com.google.dagger:hilt-android-gradle-plugin:$hilt_dagger_version"
     }
 }