Added tabbing navigation tutorial. (#817)

* Added tabbing navigation tutorial.

README.md

@@ -38,6 +38,7 @@ Preview functionality (check your application UI without building/running it) fo
        * [Top level windows management](tutorials/Window_API_new)
        * [Menu, tray, notifications](tutorials/Tray_Notifications_MenuBar_new)
        * [Keyboard support](tutorials/Keyboard)
+       * [Tab focus navigation](tutorials/Tab_Navigation)
        * [Building native distribution](tutorials/Native_distributions_and_local_execution)
        * [Signing and notarization](tutorials/Signing_and_notarization_on_macOS)
        * [Swing interoperability](tutorials/Swing_Integration)

tutorials/Tab_Navigation/README.md

@@ -0,0 +1,312 @@
+# Tabbing navigation and keyboard focus
+
+## What is covered
+
+In this tutorial, we will show you how to use tabbing navigation between components via keyboard shortcuts `tab` and `shift + tab`.
+
+## Default `Next/Previous` tabbing navigation
+
+By default, `Next/Previous` tabbed navigation moves focus in composition order (in order of appearance), to see how this works, we can use some of the components that are already focusable by default:`TextField`, `OutlinedTextField`, `BasicTextField`, `CircularProgressIndicator`, `LinearProgressIndicator`.
+
+```kotlin
+import androidx.compose.ui.window.application
+import androidx.compose.ui.window.Window
+import androidx.compose.ui.window.WindowState
+import androidx.compose.ui.window.WindowSize
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+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.material.OutlinedTextField
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+
+fun main() = application {
+    Window(
+        state = WindowState(size = WindowSize(350.dp, 500.dp)),
+        onCloseRequest = ::exitApplication
+    ) {
+        Box(
+            modifier = Modifier.fillMaxSize(),
+            contentAlignment = Alignment.Center
+        ) {
+            Column(
+                modifier = Modifier.padding(50.dp)
+            ) {
+                for (x in 1..5) {
+                    val text = remember { mutableStateOf("") }
+                    OutlinedTextField(
+                        value = text.value,
+                        singleLine = true,
+                        onValueChange = { text.value = it }
+                    )
+                    Spacer(modifier = Modifier.height(20.dp))
+                }
+            }
+        }
+    }
+}
+```
+
+![default-tab-nav](default-tab-nav.gif)
+
+To make a non-focusable component focusable, you need to apply `Modifier.focusable()` modifier to the component.
+
+```kotlin
+import androidx.compose.ui.window.application
+import androidx.compose.ui.window.Window
+import androidx.compose.ui.window.WindowState
+import androidx.compose.ui.window.WindowSize
+import androidx.compose.material.Button
+import androidx.compose.material.ButtonDefaults
+import androidx.compose.material.MaterialTheme
+import androidx.compose.material.Text
+import androidx.compose.foundation.focusable
+import androidx.compose.foundation.interaction.collectIsFocusedAsState
+import androidx.compose.foundation.interaction.MutableInteractionSource
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.lerp
+import androidx.compose.ui.ExperimentalComposeUiApi
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.IntSize
+import androidx.compose.ui.input.key.KeyEventType
+import androidx.compose.ui.input.key.type
+import androidx.compose.ui.input.key.key
+import androidx.compose.ui.input.key.Key
+import androidx.compose.ui.input.key.onPreviewKeyEvent
+
+fun main() = application {
+    Window(
+        state = WindowState(size = WindowSize(350.dp, 450.dp)),
+        onCloseRequest = ::exitApplication
+    ) {
+        MaterialTheme(
+            colors = MaterialTheme.colors.copy(
+                primary = Color(10, 132, 232),
+                secondary = Color(150, 232, 150)
+            )
+        ) {
+            val clicks = remember { mutableStateOf(0) }
+            Box(
+                modifier = Modifier.fillMaxSize(),
+                contentAlignment = Alignment.Center
+            ) {
+                Column(
+                    modifier = Modifier.padding(40.dp)
+                ) {
+                    Text(text = "Clicks: ${clicks.value}")
+                    Spacer(modifier = Modifier.height(20.dp))
+                    for (x in 1..5) {
+                        FocusableButton("Button $x", { clicks.value++ })
+                        Spacer(modifier = Modifier.height(20.dp))
+                    }
+                }
+            }
+        }
+    }
+}
+
+@OptIn(ExperimentalComposeUiApi::class)
+@Composable
+fun FocusableButton(
+    text: String = "",
+    onClick: () -> Unit = {},
+    size: IntSize = IntSize(200, 35)
+) {
+    val keyPressedState = remember { mutableStateOf(false) }
+    val interactionSource = remember { MutableInteractionSource() }
+    val colors = ButtonDefaults.buttonColors(
+        backgroundColor = if (interactionSource.collectIsFocusedAsState().value) {
+            if (keyPressedState.value)
+                lerp(MaterialTheme.colors.secondary, Color(64, 64, 64), 0.3f)
+            else
+                MaterialTheme.colors.secondary
+        } else {
+            MaterialTheme.colors.primary
+        }
+    )
+    Button(
+        onClick = onClick,
+        interactionSource = interactionSource,
+        modifier = Modifier.size(size.width.dp, size.height.dp)
+            .onPreviewKeyEvent {
+                if (
+                    it.key == Key.Enter ||
+                    it.key == Key.Spacebar
+                ) {
+                    when (it.type) {
+                        KeyEventType.KeyDown -> {
+                            keyPressedState.value = true
+                        }
+                        KeyEventType.KeyUp -> {
+                            keyPressedState.value = false
+                            onClick.invoke()
+                        }
+                    }
+                }
+                false
+            }
+            .focusable(interactionSource = interactionSource),
+        colors = colors
+    ) {
+        Text(text = text)
+    }
+}
+```
+
+![focusable-buttons](focusable-button.gif)
+
+## Custom ordering
+To move focus in custom order we need to create a `FocusRequester` and apply the `Modifier.focusOrder` modifier to each component you want to navigate.
+
+- `FocusRequester` sends requests to change focus.
+- `Modifier.focusOrder` is used to specify a custom focus traversal order.
+
+In the example below, we simply create a `FocusRequester` list and create text fields for each `FocusRequester` in the list. Each text field sends a focus request to the previous and next text field in the list when using the `shift + tab` or `tab` keyboard shortcut in reverse order.
+
+```kotlin
+import androidx.compose.ui.window.application
+import androidx.compose.ui.window.Window
+import androidx.compose.ui.window.WindowState
+import androidx.compose.ui.window.WindowSize
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+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.material.OutlinedTextField
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.ui.focus.FocusRequester
+import androidx.compose.ui.focus.focusOrder
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+
+fun main() = application {
+    Window(
+        state = WindowState(size = WindowSize(350.dp, 500.dp)),
+        onCloseRequest = ::exitApplication
+    ) {
+        val itemsList = remember { List(5) { FocusRequester() } }
+        Box(
+            modifier = Modifier.fillMaxSize(),
+            contentAlignment = Alignment.Center
+        ) {
+            Column(
+                modifier = Modifier.padding(50.dp)
+            ) {
+                itemsList.forEachIndexed { index, item ->
+                    val text = remember { mutableStateOf("") }
+                    OutlinedTextField(
+                        value = text.value,
+                        singleLine = true,
+                        onValueChange = { text.value = it },
+                        modifier = Modifier.focusOrder(item) {
+                            // reverse order
+                            next = if (index - 1 < 0) itemsList.last() else itemsList[index - 1]
+                            previous = if (index + 1 == itemsList.size) itemsList.first() else itemsList[index + 1]
+                        }
+                    )
+                    Spacer(modifier = Modifier.height(20.dp))
+                }
+            }
+        }
+    }
+}
+```
+
+![reverse-order](reverse-order.gif)
+
+## Making component focused
+
+To make a component focused, we need to create a `FocusRequester` and apply the `Modifier.focusRequester` modifier to the component you want to focus on. With `FocusRequester`, we can request focus, as in the example below:
+
+```kotlin
+import androidx.compose.ui.window.application
+import androidx.compose.ui.window.Window
+import androidx.compose.ui.window.WindowState
+import androidx.compose.ui.window.WindowSize
+import androidx.compose.foundation.focusable
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.material.Button
+import androidx.compose.material.OutlinedTextField
+import androidx.compose.material.Text
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.ui.focus.FocusRequester
+import androidx.compose.ui.focus.focusRequester
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.dp
+
+fun main() = application {
+    Window(
+        state = WindowState(size = WindowSize(350.dp, 450.dp)),
+        onCloseRequest = ::exitApplication
+    ) {
+        val buttonFocusRequester = remember { FocusRequester() }
+        val textFieldFocusRequester = remember { FocusRequester() }
+        val focusState = remember { mutableStateOf(false) }
+        val text = remember { mutableStateOf("") }
+        Box(
+            modifier = Modifier.fillMaxSize(),
+            contentAlignment = Alignment.Center
+        ) {
+            Column(
+                modifier = Modifier.padding(50.dp)
+            ) {
+                Button(
+                    onClick = {
+                        focusState.value = !focusState.value
+                        if (focusState.value) {
+                            textFieldFocusRequester.requestFocus()
+                        } else {
+                            buttonFocusRequester.requestFocus()
+                        }
+                    },
+                    modifier = Modifier.fillMaxWidth()
+                        .focusRequester(buttonFocusRequester)
+                        .focusable()
+                ) {
+                    Text(text = "Focus switcher")
+                }
+                Spacer(modifier = Modifier.height(20.dp))
+                OutlinedTextField(
+                    value = text.value,
+                    singleLine = true,
+                    onValueChange = { text.value = it },
+                    modifier = Modifier
+                        .focusRequester(textFieldFocusRequester)
+                )
+            }
+        }
+    }
+}
+```
+
+![reverse-order](focus-switcher.gif)