Refactoring: introduce DocumentUiModel

app/src/main/java/org/mydomain/myscan/MainActivity.kt

@@ -58,7 +58,7 @@ class MainActivity : ComponentActivity() {
         setContent {
             val currentScreen by viewModel.currentScreen.collectAsStateWithLifecycle()
             val liveAnalysisState by viewModel.liveAnalysisState.collectAsStateWithLifecycle()
-            val pageIds by viewModel.pageIds.collectAsStateWithLifecycle()
+            val document by viewModel.documentUiModel.collectAsStateWithLifecycle()
             MyScanTheme {
                 val navigation = Navigation(
                     toCameraScreen = { viewModel.navigateTo(Screen.Camera) },
@@ -78,9 +78,8 @@ class MainActivity : ComponentActivity() {
                     }
                     is Screen.Document -> {
                         DocumentScreen (
-                            pageIds,
+                            document = document,
                             initialPage = screen.initialPage,
-                            imageLoader = { id -> viewModel.getBitmap(id) },
                             navigation = navigation,
                             pdfActions = PdfGenerationActions(
                                 startGeneration = viewModel::startPdfGeneration,

app/src/main/java/org/mydomain/myscan/MainViewModel.kt

@@ -38,6 +38,7 @@ import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
 import org.mydomain.myscan.ui.PdfGenerationUiState
+import org.mydomain.myscan.view.DocumentUiModel
 import java.io.ByteArrayOutputStream
 import java.io.File
 
@@ -71,8 +72,18 @@ class MainViewModel(
     val currentScreen: StateFlow<Screen> = _screenStack.map { it.last() }
         .stateIn(viewModelScope, SharingStarted.Eagerly, Screen.Camera)
 
-    private val _pageIds = MutableStateFlow<List<String>>(imageRepository.imageIds())
-    val pageIds: StateFlow<List<String>> = _pageIds
+    private val _pageIds = MutableStateFlow(imageRepository.imageIds())
+    val documentUiModel: StateFlow<DocumentUiModel> =
+        _pageIds.map { ids ->
+            DocumentUiModel(
+                pageIds = ids,
+                imageLoader = ::getBitmap
+            )
+        }.stateIn(
+            scope = viewModelScope,
+            started = SharingStarted.Eagerly,
+            initialValue = DocumentUiModel(emptyList(), ::getBitmap)
+        )
 
     private val _captureState = MutableStateFlow<CaptureState>(CaptureState.Idle)
     val captureState: StateFlow<CaptureState> = _captureState

app/src/main/java/org/mydomain/myscan/view/CameraScreen.kt

@@ -101,7 +101,7 @@ fun CameraScreen(
     onFinalizePressed: () -> Unit,
 ) {
     var previewView by remember { mutableStateOf<PreviewView?>(null) }
-    val pageIds by viewModel.pageIds.collectAsStateWithLifecycle()
+    val document by viewModel.documentUiModel.collectAsStateWithLifecycle()
     val thumbnailCoords = remember { mutableStateOf(Offset.Zero) }
     var isDebugMode by remember { mutableStateOf(false) }
 
@@ -129,9 +129,9 @@ fun CameraScreen(
     }
 
     val listState = rememberLazyListState()
-    LaunchedEffect(pageIds.size) {
-        if (pageIds.isNotEmpty()) {
-            listState.animateScrollToItem(pageIds.lastIndex)
+    LaunchedEffect(document.pageCount()) {
+        if (!document.isEmpty()) {
+            listState.animateScrollToItem(document.lastIndex())
         }
     }
     val isLandscape = LocalConfiguration.current.orientation == Configuration.ORIENTATION_LANDSCAPE
@@ -145,14 +145,13 @@ fun CameraScreen(
         },
         pageListState =
             CommonPageListState(
-                pageIds = pageIds,
-                imageLoader = { id -> viewModel.getBitmap(id) },
+                document = document,
                 onPageClick = { index -> viewModel.navigateTo(Screen.Document(index)) },
                 listState = listState,
                 onLastItemPosition = { offset -> thumbnailCoords.value = offset },
             ),
         cameraUiState = CameraUiState(
-            pageIds.size,
+            document.pageCount(),
             liveAnalysisState,
             captureState,
             showDetectionError,
@@ -457,12 +456,13 @@ private fun ScreenPreview(captureState: CaptureState, rotationDegrees: Float = 0
             },
             pageListState =
                 CommonPageListState(
-                    pageIds = listOf(1, 2, 2, 2).map { "gallica.bnf.fr-bpt6k5530456s-$it.jpg" },
-                    imageLoader = { id ->
-                        context.assets.open(id).use { input ->
-                            BitmapFactory.decodeStream(input)
-                        }
-                    },
+                    document = DocumentUiModel(
+                        pageIds = listOf(1, 2, 2, 2).map { "gallica.bnf.fr-bpt6k5530456s-$it.jpg" },
+                        imageLoader = { id ->
+                            context.assets.open(id).use { input ->
+                                BitmapFactory.decodeStream(input)
+                            }
+                        }),
                     onPageClick = {},
                     listState = LazyListState(),
                 ),

app/src/main/java/org/mydomain/myscan/view/DocumentScreen.kt

@@ -14,7 +14,6 @@
  */
 package org.mydomain.myscan.view
 
-import android.graphics.Bitmap
 import android.graphics.BitmapFactory
 import androidx.activity.compose.BackHandler
 import androidx.compose.foundation.Image
@@ -68,9 +67,8 @@ import org.mydomain.myscan.ui.theme.MyScanTheme
 @OptIn(ExperimentalMaterial3Api::class)
 @Composable
 fun DocumentScreen(
-    pageIds: List<String>,
+    document: DocumentUiModel,
     initialPage: Int,
-    imageLoader: (String) -> Bitmap?,
     navigation: Navigation,
     pdfActions: PdfGenerationActions,
     onStartNew: () -> Unit,
@@ -80,8 +78,8 @@ fun DocumentScreen(
     val showNewDocDialog = rememberSaveable { mutableStateOf(false) }
     val showPdfDialog = rememberSaveable { mutableStateOf(false) }
     val currentPageIndex = rememberSaveable { mutableIntStateOf(initialPage) }
-    if (currentPageIndex.intValue >= pageIds.size) {
-        currentPageIndex.intValue = pageIds.size - 1
+    if (currentPageIndex.intValue >= document.pageCount()) {
+        currentPageIndex.intValue = document.pageCount() - 1
     }
     if (currentPageIndex.intValue < 0) {
         navigation.toCameraScreen()
@@ -97,8 +95,7 @@ fun DocumentScreen(
     MyScaffold(
         toAboutScreen = navigation.toAboutScreen,
         pageListState = CommonPageListState(
-            pageIds,
-            imageLoader,
+            document,
             onPageClick = { index -> currentPageIndex.intValue = index },
             currentPageIndex = currentPageIndex.intValue,
             listState = listState,
@@ -115,7 +112,7 @@ fun DocumentScreen(
             )
         },
     ) { modifier ->
-        DocumentPreview(pageIds, imageLoader, currentPageIndex, onDeleteImage, modifier)
+        DocumentPreview(document, currentPageIndex, onDeleteImage, modifier)
         if (showNewDocDialog.value) {
             NewDocumentDialog(onConfirm = onStartNew, showNewDocDialog)
         }
@@ -130,21 +127,20 @@ fun DocumentScreen(
 
 @Composable
 private fun DocumentPreview(
-    pageIds: List<String>,
-    imageLoader: (String) -> Bitmap?,
+    document: DocumentUiModel,
     currentPageIndex: MutableIntState,
     onDeleteImage: (String) -> Unit,
     modifier: Modifier,
 ) {
-    val imageId = pageIds[currentPageIndex.intValue]
+    val imageId = document.pageId(currentPageIndex.intValue)
     Column (
         modifier = modifier
             .background(MaterialTheme.colorScheme.surfaceContainerLow)
     ) {
         Box (
             modifier = Modifier.fillMaxSize()
         ) {
-            val bitmap = imageLoader(imageId)
+            val bitmap = document.load(currentPageIndex.intValue)
             if (bitmap != null) {
                 val imageBitmap = bitmap.asImageBitmap()
                 val zoomState = rememberZoomState(
@@ -175,7 +171,7 @@ private fun DocumentPreview(
                     .align(Alignment.BottomEnd)
                     .padding(8.dp)
             )
-            Text("${currentPageIndex.intValue + 1} / ${pageIds.size}",
+            Text("${currentPageIndex.intValue + 1} / ${document.pageCount()}",
                 color = MaterialTheme.colorScheme.inverseOnSurface,
                 modifier = Modifier
                     .align(Alignment.BottomStart)
@@ -243,13 +239,15 @@ fun DocumentScreenPreview() {
     val context = LocalContext.current
     MyScanTheme {
         DocumentScreen(
-            pageIds = listOf(1, 2, 2, 2).map { "gallica.bnf.fr-bpt6k5530456s-$it.jpg" },
-            initialPage = 1,
-            imageLoader = { id ->
-                context.assets.open(id).use { input ->
-                    BitmapFactory.decodeStream(input)
+            DocumentUiModel(
+                listOf(1, 2, 2, 2).map { "gallica.bnf.fr-bpt6k5530456s-$it.jpg" },
+                { id ->
+                    context.assets.open(id).use { input ->
+                        BitmapFactory.decodeStream(input)
+                    }
                 }
-            },
+            ),
+            initialPage = 1,
             navigation = Navigation(
                 {}, {}, {}, {}, {}),
             pdfActions = PdfGenerationActions(

app/src/main/java/org/mydomain/myscan/view/DocumentUiModel.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2025 Pierre-Yves Nicolas
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option)
+ * any later version.
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.mydomain.myscan.view
+
+import android.graphics.Bitmap
+
+data class DocumentUiModel(
+    private val pageIds: List<String>,
+    private val imageLoader: (String) -> Bitmap?
+) {
+    fun pageCount(): Int {
+        return pageIds.size
+    }
+    fun pageId(index: Int): String {
+        return pageIds[index]
+    }
+    fun isEmpty(): Boolean {
+        return pageIds.isEmpty()
+    }
+    fun lastIndex(): Int {
+        return pageIds.lastIndex
+    }
+    fun load(index: Int): Bitmap? {
+        return imageLoader(pageIds[index])
+    }
+}

app/src/main/java/org/mydomain/myscan/view/PageList.kt

@@ -28,9 +28,9 @@ import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.LazyListScope
 import androidx.compose.foundation.lazy.LazyListState
 import androidx.compose.foundation.lazy.LazyRow
-import androidx.compose.foundation.lazy.itemsIndexed
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
@@ -51,8 +51,7 @@ import androidx.compose.ui.unit.sp
 const val PAGE_LIST_ELEMENT_SIZE_DP = 120
 
 data class CommonPageListState(
-    val pageIds: List<String>,
-    val imageLoader: (String) -> Bitmap?,
+    val document: DocumentUiModel,
     val onPageClick: (Int) -> Unit,
     val listState: LazyListState,
     val currentPageIndex: Int? = null,
@@ -65,37 +64,32 @@ fun CommonPageList(
     modifier: Modifier = Modifier,
 ) {
     val isLandscape = LocalConfiguration.current.orientation == Configuration.ORIENTATION_LANDSCAPE
+    val content: LazyListScope.() -> Unit = {
+        items(state.document.pageCount()) { index ->
+            // TODO Use small images rather than big ones
+            val image = state.document.load(index)
+            if (image != null) {
+                PageThumbnail(image, index, state)
+            }
+        }
+    }
     if (isLandscape) {
         LazyColumn (
             horizontalAlignment = Alignment.CenterHorizontally,
-            modifier = modifier
-        ) {
-            itemsIndexed(state.pageIds) { index, id ->
-                // TODO Use small images rather than big ones
-                val image = state.imageLoader(id)
-                if (image != null) {
-                    PageThumbnail(image, index, state)
-                }
-            }
-        }
+            modifier = modifier,
+            content = content,
+        )
     } else {
         LazyRow (
             state = state.listState,
             contentPadding = PaddingValues(4.dp),
             modifier = Modifier.fillMaxWidth().background(MaterialTheme.colorScheme.surfaceContainer),
             horizontalArrangement = Arrangement.spacedBy(8.dp),
-            verticalAlignment = Alignment.CenterVertically
-        ) {
-            itemsIndexed(state.pageIds) { index, id ->
-                // TODO Use small images rather than big ones
-                val image = state.imageLoader(id)
-                if (image != null) {
-                    PageThumbnail(image, index, state)
-                }
-            }
-        }
+            verticalAlignment = Alignment.CenterVertically,
+            content = content,
+        )
     }
-    if (state.pageIds.isEmpty()) {
+    if (state.document.isEmpty()) {
         Box(
             modifier = Modifier
                 .height(120.dp)
@@ -120,7 +114,7 @@ private fun PageThumbnail(
             Modifier.height(maxImageSize)
         else
             Modifier.width(maxImageSize)
-    if (index == state.pageIds.lastIndex) {
+    if (index == state.document.lastIndex()) {
         val density = LocalDensity.current
         modifier = modifier.addPositionCallback(state.onLastItemPosition, density, 1.0f)
     }