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.unit.LayoutDirection.Ltr
import androidx.compose.ui.unit.LayoutDirection.Rtl
import androidx.compose.ui.focus.FocusDirection.Down
import androidx.compose.ui.focus.FocusDirection.Left
import androidx.compose.ui.focus.FocusDirection.Next
import androidx.compose.ui.focus.FocusDirection.Previous
import androidx.compose.ui.focus.FocusDirection.Right
import androidx.compose.ui.focus.FocusDirection.Up
import androidx.compose.ui.focus.FocusState.Active
import androidx.compose.ui.focus.FocusRequester.Companion.Default
import androidx.compose.ui.node.ModifiedFocusNode
/**
* This enum specifies the direction of the requested focus change.
*/
internal enum class FocusDirection { Next, Previous, Left, Right, Up, Down }
/**
* Moves focus based on the requested focus direction.
*
* @param focusDirection The requested direction to move focus.
* @return whether focus was moved or not.
*/
internal fun ModifiedFocusNode.moveFocus(focusDirection: FocusDirection): Boolean {
check(modifier.focusState == Active)
// 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 = customFocusSearch(focusDirection)
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.
return when (focusDirection) {
Next, Previous -> {
// TODO(b/170155659): Perform one dimensional focus search.
false
}
Left, Right, Up, Down -> {
// TODO(b/170155926): Perform two dimensional focus search.
false
}
}
}
/**
* 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): FocusRequester {
val focusOrder = FocusOrder()
wrappedBy?.populateFocusOrder(focusOrder)
// TODO(b/176847718): Pass the layout direction as a parameter to customFocusSearch, and use
// that instead of this hardcoded value.
val layoutDirection = Ltr
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
}
}