Use Channel and Flow to avoid duplicate events

app/src/main/java/org/thoughtcrime/securesms/conversation/v2/MessageDetailActivity.kt

@@ -32,8 +32,8 @@ import androidx.compose.material.LocalTextStyle
 import androidx.compose.material.Surface
 import androidx.compose.material.Text
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
-import androidx.compose.runtime.livedata.observeAsState
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
@@ -48,13 +48,14 @@ import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.tooling.preview.PreviewParameter
 import androidx.compose.ui.unit.dp
 import androidx.compose.ui.viewinterop.AndroidView
-import androidx.core.content.ContextCompat
+import androidx.lifecycle.lifecycleScope
 import com.bumptech.glide.integration.compose.ExperimentalGlideComposeApi
 import com.bumptech.glide.integration.compose.GlideImage
 import dagger.hilt.android.AndroidEntryPoint
+import kotlinx.coroutines.launch
 import network.loki.messenger.R
 import network.loki.messenger.databinding.ViewVisibleMessageContentBinding
-import org.thoughtcrime.securesms.MediaPreviewActivity
+import org.thoughtcrime.securesms.MediaPreviewActivity.getPreviewIntent
 import org.thoughtcrime.securesms.PassphraseRequiredActionBarActivity
 import org.thoughtcrime.securesms.database.Storage
 import org.thoughtcrime.securesms.ui.AppTheme
@@ -102,23 +103,25 @@ class MessageDetailActivity : PassphraseRequiredActionBarActivity() {
 
         intent.getLongExtra(MESSAGE_TIMESTAMP, -1L).let(viewModel::setMessageTimestamp)
 
-        if (viewModel.state.value == null) {
-            finish()
-            return
-        }
-
         ComposeView(this)
             .apply { setContent { MessageDetailsScreen() } }
             .let(::setContentView)
 
-        viewModel.event.observe(this) {
+        lifecycleScope.launch {
-            startActivity(MediaPreviewActivity.getPreviewIntent(this, it))
+            viewModel.eventFlow.collect {
+                when (it) {
+                    Event.Finish -> finish()
+                    is Event.StartMediaPreview -> startActivity(
+                        getPreviewIntent(this@MessageDetailActivity, it.args)
+                    )
+                }
+            }
         }
     }
 
     @Composable
     private fun MessageDetailsScreen() {
-        val state by viewModel.state.observeAsState(MessageDetailsState())
+        val state by viewModel.stateFlow.collectAsState()
         AppTheme {
             MessageDetails(
                 state = state,

app/src/main/java/org/thoughtcrime/securesms/conversation/v2/MessageDetailsViewModel.kt

@@ -1,12 +1,14 @@
 package org.thoughtcrime.securesms.conversation.v2
 
 import android.net.Uri
-import androidx.lifecycle.LiveData
-import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import dagger.hilt.android.lifecycle.HiltViewModel
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.flow.receiveAsFlow
 import kotlinx.coroutines.launch
 import network.loki.messenger.R
 import org.session.libsession.messaging.jobs.AttachmentDownloadJob
@@ -38,17 +40,23 @@ class MessageDetailsViewModel @Inject constructor(
     private val threadDb: ThreadDatabase,
 ) : ViewModel() {
 
-    private var _state = MutableLiveData(MessageDetailsState())
+    private val state = MutableStateFlow(MessageDetailsState())
-    val state: LiveData<MessageDetailsState> = _state
+    val stateFlow = state.asStateFlow()
 
-    private var _event = MutableLiveData<MediaPreviewArgs>()
+    private val event = Channel<Event>()
-    val event: LiveData<MediaPreviewArgs> = _event
+    val eventFlow = event.receiveAsFlow()
 
     fun setMessageTimestamp(timestamp: Long) {
-        val record = mmsSmsDatabase.getMessageForTimestamp(timestamp) ?: return
+        val record = mmsSmsDatabase.getMessageForTimestamp(timestamp)
+
+        if (record == null) {
+            viewModelScope.launch { event.send(Event.Finish) }
+            return
+        }
+
         val mmsRecord = record as? MmsMessageRecord
 
-        _state.value = record.run {
+        state.value = record.run {
             val slides = mmsRecord?.slideDeck?.slides ?: emptyList()
 
             MessageDetailsState(
@@ -106,9 +114,12 @@ class MessageDetailsViewModel @Inject constructor(
 
         if (slide.isInProgress) return
 
-        _event.value = MediaPreviewArgs(slide, state.mmsRecord, state.thread)
+        viewModelScope.launch {
+            MediaPreviewArgs(slide, state.mmsRecord, state.thread)
+                .let(Event::StartMediaPreview)
+                .let { event.send(it) }
+        }
     }
-
 
     fun onAttachmentNeedsDownload(attachmentId: Long, mmsId: Long) {
         viewModelScope.launch(Dispatchers.IO) {
@@ -139,3 +150,8 @@ data class Attachment(
     val uri: Uri?,
     val hasImage: Boolean
 )
+
+sealed class Event {
+    object Finish: Event()
+    data class StartMediaPreview(val args: MediaPreviewArgs): Event()
+}