FocusTraversal.kt
/*
* Copyright 2020 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.compose.ui.focus
import androidx.compose.ui.ExperimentalComposeUiApi
import androidx.compose.ui.focus.FocusDirection.Companion.Down
import androidx.compose.ui.focus.FocusDirection.Companion.In
import androidx.compose.ui.focus.FocusDirection.Companion.Left
import androidx.compose.ui.focus.FocusDirection.Companion.Next
import androidx.compose.ui.focus.FocusDirection.Companion.Out
import androidx.compose.ui.focus.FocusDirection.Companion.Previous
import androidx.compose.ui.focus.FocusDirection.Companion.Right
import androidx.compose.ui.focus.FocusDirection.Companion.Up
import androidx.compose.ui.focus.FocusRequester.Companion.Default
import androidx.compose.ui.focus.FocusStateImpl.Active
import androidx.compose.ui.focus.FocusStateImpl.ActiveParent
import androidx.compose.ui.focus.FocusStateImpl.Captured
import androidx.compose.ui.focus.FocusStateImpl.Disabled
import androidx.compose.ui.focus.FocusStateImpl.Inactive
import androidx.compose.ui.node.ModifiedFocusNode
import androidx.compose.ui.unit.LayoutDirection
import androidx.compose.ui.unit.LayoutDirection.Ltr
import androidx.compose.ui.unit.LayoutDirection.Rtl
private const val invalidFocusDirection = "Invalid FocusDirection"
/**
* The [FocusDirection] is used to specify direction when a focus change request is made via
* [moveFocus].
*
* @sample androidx.compose.ui.samples.MoveFocusSample
*/
@Suppress("INLINE_CLASS_DEPRECATED", "EXPERIMENTAL_FEATURE_WARNING")
inline class FocusDirection(val value: Int) {
override fun toString(): String {
return when (this) {
Next -> "Next"
Previous -> "Previous"
Left -> "Left"
Right -> "Right"
Up -> "Up"
Down -> "Down"
@OptIn(ExperimentalComposeUiApi::class)
In -> "In"
@OptIn(ExperimentalComposeUiApi::class)
Out -> "Out"
else -> invalidFocusDirection
}
}
companion object {
/**
* Direction used in [moveFocus] to indicate that you are searching for the next
* focusable item.
*/
val Next: FocusDirection = FocusDirection(1)
/**
* Direction used in [moveFocus] to indicate that you are searching for the previous
* focusable item.
*/
val Previous: FocusDirection = FocusDirection(2)
/**
* Direction used in [moveFocus] to indicate that you are searching for the next
* focusable item to the left of the currently focused item.
*/
val Left: FocusDirection = FocusDirection(3)
/**
* Direction used in [moveFocus] to indicate that you are searching for the next
* focusable item to the right of the currently focused item.
*/
val Right: FocusDirection = FocusDirection(4)
/**
* Direction used in [moveFocus] to indicate that you are searching for the next
* focusable item that is above the currently focused item.
*/
val Up: FocusDirection = FocusDirection(5)
/**
* Direction used in [moveFocus] to indicate that you are searching for the next
* focusable item that is below the currently focused item.
*/
val Down: FocusDirection = FocusDirection(6)
/**
* Direction used in [moveFocus] to indicate that you are searching for the next
* focusable item that is a child of the currently focused item.
*/
@ExperimentalComposeUiApi
val In: FocusDirection = FocusDirection(7)
/**
* Direction used in [moveFocus] to indicate that you want to move focus to the parent
* of the currently focused item.
*/
@ExperimentalComposeUiApi
val Out: FocusDirection = FocusDirection(8)
}
}
/**
* Moves focus based on the requested focus direction.
*
* @param focusDirection The requested direction to move focus.
* @return whether a focus node was found. If a focus node was found and the focus request was
* not granted, this function still returns true.
*/
internal fun ModifiedFocusNode.moveFocus(focusDirection: FocusDirection): Boolean {
// TODO(b/176847718): Pass the layout direction as a parameter instead of this hardcoded value.
val layoutDirection: LayoutDirection = Ltr
// If there is no active node in this sub-hierarchy, we can't move focus.
val activeNode = findActiveFocusNode() ?: return false
// TODO(b/175899779) If the direction is "Next", cache the current node so we can come back
// to the same place if the user requests "Previous"
// Check if a custom focus traversal order is specified.
val nextFocusRequester = activeNode.customFocusSearch(focusDirection, layoutDirection)
if (nextFocusRequester != Default) {
// TODO(b/175899786): We ideally need to check if the nextFocusRequester points to something
// that is visible and focusable in the current mode (Touch/Non-Touch mode).
nextFocusRequester.requestFocus()
return true
}
// If no custom focus traversal order is specified, perform a search for the appropriate item
// to move focus to.
val nextNode = when (focusDirection) {
Next, Previous -> null // TODO(b/170155659): Perform one dimensional focus search.
Left, Right, Up, Down -> twoDimensionalFocusSearch(focusDirection)
@OptIn(ExperimentalComposeUiApi::class)
In -> {
// we search among the children of the active item.
val direction = when (layoutDirection) { Rtl -> Left; Ltr -> Right }
activeNode.twoDimensionalFocusSearch(direction)
}
@OptIn(ExperimentalComposeUiApi::class)
Out -> activeNode.findParentFocusNode()
else -> error(invalidFocusDirection)
} ?: return false
// If we found a potential next item, call requestFocus() to move focus to it.
nextNode.requestFocus(propagateFocus = false)
return true
}
internal fun ModifiedFocusNode.findActiveFocusNode(): ModifiedFocusNode? {
return when (focusState) {
Active, Captured -> this
ActiveParent -> focusedChild?.findActiveFocusNode()
Inactive, Disabled -> null
}
}
/**
* Search up the component tree for any parent/parents that have specified a custom focus order.
* Allowing parents higher up the hierarchy to overwrite the focus order specified by their
* children.
*/
private fun ModifiedFocusNode.customFocusSearch(
focusDirection: FocusDirection,
layoutDirection: LayoutDirection
): FocusRequester {
val focusOrder = FocusOrder()
wrappedBy?.populateFocusOrder(focusOrder)
return when (focusDirection) {
Next -> focusOrder.next
Previous -> focusOrder.previous
Up -> focusOrder.up
Down -> focusOrder.down
Left -> when (layoutDirection) {
Ltr -> focusOrder.start
Rtl -> focusOrder.end
}.takeUnless { it == Default } ?: focusOrder.left
Right -> when (layoutDirection) {
Ltr -> focusOrder.end
Rtl -> focusOrder.start
}.takeUnless { it == Default } ?: focusOrder.right
// TODO(b/183746982): add focus order API for "In" and "Out".
// Developers can to specify a custom "In" to specify which child should be visited when
// the user presses dPad center. (They can also redirect the "In" to some other item).
// Developers can specify a custom "Out" to specify which composable should take focus
// when the user presses the back button.
@OptIn(ExperimentalComposeUiApi::class)
In -> Default
@OptIn(ExperimentalComposeUiApi::class)
Out -> Default
else -> error(invalidFocusDirection)
}
}