FocusManager.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.Modifier
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.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.unit.LayoutDirection
interface FocusManager {
/**
* Call this function to clear focus from the currently focused component, and set the focus to
* the root focus modifier.
*
* @param force: Whether we should forcefully clear focus regardless of whether we have
* any components that have Captured focus.
*
* @sample androidx.compose.ui.samples.ClearFocusSample
*/
fun clearFocus(force: Boolean = false)
/**
* Moves focus in the specified [direction][FocusDirection].
*
* If you are not satisfied with the default focus order, consider setting a custom order using
* [Modifier.focusOrder()][focusOrder].
*
* @return true if focus was moved successfully. false if the focused item is unchanged.
*
* @sample androidx.compose.ui.samples.MoveFocusSample
*/
fun moveFocus(focusDirection: FocusDirection): Boolean
}
/**
* The focus manager is used by different [Owner][androidx.compose.ui.node.Owner] implementations
* to control focus.
*
* @param focusModifier The modifier that will be used as the root focus modifier.
*/
internal class FocusManagerImpl(
private val focusModifier: FocusModifier = FocusModifier(Inactive)
) : FocusManager {
/**
* A [Modifier] that can be added to the [Owners][androidx.compose.ui.node.Owner] modifier
* list that contains the modifiers required by the focus system. (Eg, a root focus modifier).
*/
val modifier: Modifier
// TODO(b/168831247): return an empty Modifier when there are no focusable children.
get() = focusModifier
lateinit var layoutDirection: LayoutDirection
/**
* The [Owner][androidx.compose.ui.node.Owner] calls this function when it gains focus. This
* informs the [focus manager][FocusManagerImpl] that the
* [Owner][androidx.compose.ui.node.Owner] gained focus, and that it should propagate this
* focus to one of the focus modifiers in the component hierarchy.
*/
fun takeFocus() {
// If the focus state is not Inactive, it indicates that the focus state is already
// set (possibly by dispatchWindowFocusChanged). So we don't update the state.
if (focusModifier.focusState == Inactive) {
focusModifier.focusState = Active
// TODO(b/152535715): propagate focus to children based on child focusability.
}
}
/**
* The [Owner][androidx.compose.ui.node.Owner] calls this function when it loses focus. This
* informs the [focus manager][FocusManagerImpl] that the
* [Owner][androidx.compose.ui.node.Owner] lost focus, and that it should clear focus from
* all the focus modifiers in the component hierarchy.
*/
fun releaseFocus() {
focusModifier.focusNode.clearFocus(forcedClear = true)
}
/**
* Call this function to set the focus to the root focus modifier.
*
* @param force: Whether we should forcefully clear focus regardless of whether we have
* any components that have captured focus.
*
* This could be used to clear focus when a user clicks on empty space outside a focusable
* component.
*/
override fun clearFocus(force: Boolean) {
// If this hierarchy had focus before clearing it, it indicates that the host view has
// focus. So after clearing focus within the compose hierarchy, we should reset the root
// focus modifier to "Active" to maintain consistency with the host view.
val rootWasFocused = when (focusModifier.focusState) {
Active, ActiveParent, Captured -> true
Disabled, Inactive -> false
}
if (focusModifier.focusNode.clearFocus(force) && rootWasFocused) {
focusModifier.focusState = Active
}
}
/**
* Moves focus in the specified direction.
*
* Focus moving is still being implemented. Right now, focus will move only if the user
* specified a custom focus traversal order for the item that is currently focused. (Using the
* [Modifier.focusOrder()][focusOrder] API).
*
* @return true if focus was moved successfully. false if the focused item is unchanged.
*/
override fun moveFocus(focusDirection: FocusDirection): Boolean {
// If there is no active node in this sub-hierarchy, we can't move focus.
val source = focusModifier.focusNode.findActiveFocusNode() ?: return false
// Check if a custom focus traversal order is specified.
val nextFocusRequester = source.customFocusSearch(focusDirection, layoutDirection)
if (nextFocusRequester != FocusRequester.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
}
val destination = focusModifier.focusNode.focusSearch(focusDirection, layoutDirection)
if (destination == null || destination == source) {
return false
}
// We don't want moveFocus to set focus to the root, as this would essentially clear focus.
if (destination.findParentFocusNode() == null) {
return when (focusDirection) {
// Skip the root and proceed to the next/previous item from the root's perspective.
Next, Previous -> {
destination.requestFocus(propagateFocus = false)
moveFocus(focusDirection)
}
// Instead of moving out to the root, we return false.
// When we return false the key event will not be consumed, but it will bubble
// up to the owner. (In the case of Android, the back key will be sent to the
// activity, where it can be handled appropriately).
@OptIn(ExperimentalComposeUiApi::class)
Out -> false
else -> error("Move focus landed at the root through an unknown path.")
}
}
// If we found a potential next item, call requestFocus() to move focus to it.
destination.requestFocus(propagateFocus = false)
return true
}
}