Scrollbar tutorial.

tutorials/Scrollbars/main.md

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+# Scrollbar usage
+
+## What is covered
+
+In this tutorial we will show you how to add scrollbars into scrollable lists using Compose for Desktop.
+
+## Scrollbars applying
+
+You can apply scrollbars to scrollable components. The scrollbar and scrollable component share a common state to synchronize with each other. For example, VerticalScrollbar can be attached to ScrollableColumn, LazyColumnFor and HorizontalScrollbar can be attached to ScrollableRow, LazyRowFor.
+
+```kotlin
+import androidx.compose.desktop.Window
+import androidx.compose.foundation.background
+import androidx.compose.foundation.HorizontalScrollbar
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxHeight
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.rememberScrollbarAdapter
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.ScrollableColumn
+import androidx.compose.foundation.ScrollableRow
+import androidx.compose.foundation.Text
+import androidx.compose.foundation.VerticalScrollbar
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.IntSize
+
+fun main() {
+    Window(title = "Scrollbars", size = IntSize(250, 400)) {
+        Box(
+            modifier = Modifier.fillMaxSize()
+                .background(color = Color(180, 180, 180))
+                .padding(10.dp)
+        ) {
+            val stateVertical = rememberScrollState(0f)
+            val stateHorizontal = rememberScrollState(0f)
+
+            ScrollableColumn(
+                modifier = Modifier.fillMaxSize()
+                    .padding(end = 12.dp, bottom = 12.dp),
+                scrollState = stateVertical
+            ) {
+                ScrollableRow(scrollState = stateHorizontal) {
+                    Column {
+                        for (item in 0..30) {
+                            TextBox("Item in ScrollableColumn #$item")
+                            if (item < 30) {
+                                Spacer(modifier = Modifier.height(5.dp))
+                            }
+                        }
+                    }
+                }
+            }
+            VerticalScrollbar(
+                modifier = Modifier.align(Alignment.CenterEnd)
+                    .fillMaxHeight(),
+                adapter = rememberScrollbarAdapter(stateVertical)
+            )
+            HorizontalScrollbar(
+                modifier = Modifier.align(Alignment.BottomStart)
+                    .fillMaxWidth()
+                    .padding(end = 12.dp),
+                adapter = rememberScrollbarAdapter(stateHorizontal)
+            )
+        }
+    }
+}
+
+@Composable
+fun TextBox(text: String = "Item") {
+    Box(
+        modifier = Modifier.height(32.dp)
+            .width(400.dp)
+            .background(color = Color(0, 0, 0, 20))
+            .padding(start = 10.dp),
+        alignment = Alignment.CenterStart
+    ) {
+        Text(text = text)
+    }
+}
+```
+
+![Scrollbars](scrollbars.gif)
+
+## Lazy scrollable components with Scrollbar
+
+You can use scrollbars with lazy scrollable components, for example, LazyColumn.
+
+```kotlin
+import androidx.compose.desktop.Window
+import androidx.compose.foundation.background
+import androidx.compose.foundation.ExperimentalFoundationApi
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxHeight
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.lazy.ExperimentalLazyDsl
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.rememberLazyListState
+import androidx.compose.foundation.rememberScrollbarAdapter
+import androidx.compose.foundation.Text
+import androidx.compose.foundation.VerticalScrollbar
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.IntSize
+
+fun main() {
+    Window(title = "Scrollbars", size = IntSize(250, 400)) {
+        LazyScrollable()
+    }
+}
+
+@OptIn(ExperimentalLazyDsl::class, ExperimentalFoundationApi::class)
+@Composable
+fun LazyScrollable() {
+    Box(
+        modifier = Modifier.fillMaxSize()
+            .background(color = Color(180, 180, 180))
+            .padding(10.dp)
+        ) {
+
+        val state = rememberLazyListState()
+        val itemCount = 1000
+
+        LazyColumn(Modifier.fillMaxSize().padding(end = 12.dp), state) {
+            items((1..itemCount).toList()) { x ->
+                TextBox("Item in ScrollableColumn #$x")
+                Spacer(modifier = Modifier.height(5.dp))
+            }
+        }
+        VerticalScrollbar(
+            modifier = Modifier.align(Alignment.CenterEnd).fillMaxHeight(),
+            adapter = rememberScrollbarAdapter(
+                scrollState = state,
+                itemCount = itemCount,
+                averageItemSize = 37.dp // TextBox height + Spacer height
+            )
+        )
+    }
+}
+
+@Composable
+fun TextBox(text: String = "Item") {
+    Box(
+        modifier = Modifier.height(32.dp)
+            .fillMaxWidth()
+            .background(color = Color(0, 0, 0, 20))
+            .padding(start = 10.dp),
+        alignment = Alignment.CenterStart
+    ) {
+        Text(text = text)
+    }
+}
+```
+
+![Lazy component](lazy_scrollbar.gif)
+
+## Theme applying
+
+The scrollbars support themes to change their appearance. Example below shows how to use DesktopTheme.
+
+```kotlin
+import androidx.compose.desktop.DesktopTheme
+import androidx.compose.desktop.Window
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxHeight
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.rememberScrollbarAdapter
+import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.ScrollableColumn
+import androidx.compose.foundation.Text
+import androidx.compose.foundation.VerticalScrollbar
+import androidx.compose.material.MaterialTheme
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.IntSize
+
+fun main() {
+    Window(title = "Scrollbars", size = IntSize(280, 400)) {
+        MaterialTheme {
+            DesktopTheme {
+                Box(
+                    modifier = Modifier.fillMaxSize()
+                        .background(color = Color(180, 180, 180))
+                        .padding(10.dp)
+                ) {
+                    val state = rememberScrollState(0f)
+        
+                    ScrollableColumn(
+                        modifier = Modifier.fillMaxSize().padding(end = 12.dp),
+                        scrollState = state
+                    ) {
+                        for (item in 0..30) {
+                            TextBox("Item in ScrollableColumn #$item")
+                            if (item < 30) {
+                                Spacer(modifier = Modifier.height(5.dp))
+                            }
+                        }
+                    }
+                    VerticalScrollbar(
+                        modifier = Modifier.align(Alignment.CenterEnd)
+                            .fillMaxHeight(),
+                        adapter = rememberScrollbarAdapter(state)
+                    )
+                }
+            }
+        }
+    }
+}
+
+@Composable
+fun TextBox(text: String = "Item") {
+    Box(
+        modifier = Modifier.height(32.dp)
+            .fillMaxWidth()
+            .background(color = Color(0, 0, 0, 20))
+            .padding(start = 10.dp),
+        alignment = Alignment.CenterStart
+    ) {
+        Text(text = text)
+    }
+}
+```
+
+![Themed scrollbar](themed_scrollbar.gif)