xref: /compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/focus/FocusRequester.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.runtime.Stable
import androidx.compose.runtime.annotation.RememberInComposition
import androidx.compose.runtime.collection.MutableVector
import androidx.compose.runtime.collection.mutableVectorOf
import androidx.compose.ui.focus.FocusDirection.Companion.Enter
import androidx.compose.ui.node.Nodes
import androidx.compose.ui.node.visitChildren

private const val FocusRequesterNotInitialized =
    """
   FocusRequester is not initialized. Here are some possible fixes:

   1. Remember the FocusRequester: val focusRequester = remember { FocusRequester() }
   2. Did you forget to add a Modifier.focusRequester() ?
   3. Are you attempting to request focus during composition? Focus requests should be made in
   response to some event. Eg Modifier.clickable { focusRequester.requestFocus() }
"""

private const val InvalidFocusRequesterInvocation =
    """
    Please check whether the focusRequester is FocusRequester.Cancel or FocusRequester.Default
    before invoking any functions on the focusRequester.
"""

/**
 * The [FocusRequester] is used in conjunction with
 * [Modifier.focusRequester][androidx.compose.ui.focus.focusRequester] to send requests to change
 * focus.
 *
 * @sample androidx.compose.ui.samples.RequestFocusSample
 * @see androidx.compose.ui.focus.focusRequester
 */
@Stable
class FocusRequester @RememberInComposition constructor() {

    internal val focusRequesterNodes: MutableVector<FocusRequesterModifierNode> = mutableVectorOf()

    /**
     * Use this function to request focus. If the system grants focus to a component associated with
     * this [FocusRequester], its [onFocusChanged] modifiers will receive a [FocusState] object
     * where [FocusState.isFocused] is true.
     *
     * @sample androidx.compose.ui.samples.RequestFocusSample
     */
    @Deprecated(
        message = "use the version the has a FocusDirection",
        replaceWith = ReplaceWith("this.requestFocus()"),
        level = DeprecationLevel.HIDDEN
    )
    fun requestFocus() {
        requestFocus(Enter)
    }

    /**
     * Use this function to request focus with a specific direction. If the system grants focus to a
     * component associated with this [FocusRequester], its [onFocusChanged] modifiers will receive
     * a [FocusState] object where [FocusState.isFocused] is true.
     *
     * @param focusDirection The direction passed to the [FocusTargetModifierNode] to indicate the
     *   direction that the focus request comes from.
     * @return `true` if the focus was successfully requested or `false` if the focus request was
     *   canceled.
     * @sample androidx.compose.ui.samples.RequestFocusSample
     */
    fun requestFocus(focusDirection: FocusDirection = Enter): Boolean = findFocusTargetNode {
        it.requestFocus(focusDirection)
    }

    internal fun findFocusTargetNode(onFound: (FocusTargetNode) -> Boolean): Boolean {
        return findFocusTarget { focusTarget ->
            if (focusTarget.fetchFocusProperties().canFocus) {
                onFound(focusTarget)
            } else {
                focusTarget.findChildCorrespondingToFocusEnter(Enter, onFound)
            }
        }
    }

    /**
     * Deny requests to clear focus.
     *
     * Use this function to send a request to capture focus. If a component captures focus, it will
     * send a [FocusState] object to its associated [onFocusChanged] modifiers where
     * [FocusState.isCaptured]() == true.
     *
     * When a component is in a Captured state, all focus requests from other components are
     * declined.
     *
     * @return true if the focus was successfully captured by one of the [focus][focusTarget]
     *   modifiers associated with this [FocusRequester]. False otherwise.
     * @sample androidx.compose.ui.samples.CaptureFocusSample
     */
    fun captureFocus(): Boolean {
        if (focusRequesterNodes.isEmpty()) {
            println("$FocusWarning: $FocusRequesterNotInitialized")
            return false
        }
        focusRequesterNodes.forEach {
            if (it.captureFocus()) {
                return true
            }
        }
        return false
    }

    /**
     * Use this function to send a request to free focus when one of the components associated with
     * this [FocusRequester] is in a Captured state. If a component frees focus, it will send a
     * [FocusState] object to its associated [onFocusChanged] modifiers where
     * [FocusState.isCaptured]() == false.
     *
     * When a component is in a Captured state, all focus requests from other components are
     * declined. .
     *
     * @return true if the captured focus was successfully released. i.e. At the end of this
     *   operation, one of the components associated with this [focusRequester] freed focus.
     * @sample androidx.compose.ui.samples.CaptureFocusSample
     */
    fun freeFocus(): Boolean {
        if (focusRequesterNodes.isEmpty()) {
            println("$FocusWarning: $FocusRequesterNotInitialized")
            return false
        }
        focusRequesterNodes.forEach {
            if (it.freeFocus()) {
                return true
            }
        }
        return false
    }

    /**
     * Use this function to request the focus target to save a reference to the currently focused
     * child in its saved instance state. After calling this, focus can be restored to the saved
     * child by making a call to [restoreFocusedChild].
     *
     * @return true if the focus target associated with this [FocusRequester] has a focused child
     *   and we successfully saved a reference to it.
     * @sample androidx.compose.ui.samples.RestoreFocusSample
     */
    fun saveFocusedChild(): Boolean {
        if (focusRequesterNodes.isEmpty()) {
            println("$FocusWarning: $FocusRequesterNotInitialized")
            return false
        }
        focusRequesterNodes.forEach { if (it.saveFocusedChild()) return true }
        return false
    }

    /**
     * Use this function to restore focus to one of the children of the node pointed to by this
     * [FocusRequester]. This restores focus to a previously focused child that was saved by using
     * [saveFocusedChild].
     *
     * @return true if we successfully restored focus to one of the children of the [focusTarget]
     *   associated with this [FocusRequester]
     * @sample androidx.compose.ui.samples.RestoreFocusSample
     */
    fun restoreFocusedChild(): Boolean {
        if (focusRequesterNodes.isEmpty()) {
            println("$FocusWarning: $FocusRequesterNotInitialized")
            return false
        }
        var success = false
        focusRequesterNodes.forEach { success = it.restoreFocusedChild() || success }
        return success
    }

    companion object {
        /**
         * Default [focusRequester], which when used in [Modifier.focusProperties][focusProperties]
         * implies that we want to use the default system focus order, that is based on the position
         * of the items on the screen.
         */
        val Default = FocusRequester()

        /**
         * Cancelled [focusRequester], which when used in
         * [Modifier.focusProperties][focusProperties] implies that we want to block focus search
         * from proceeding in the specified [direction][FocusDirection].
         *
         * @sample androidx.compose.ui.samples.CancelFocusMoveSample
         */
        val Cancel = FocusRequester()

        /** Used to indicate that the focus has been redirected during an enter/exit lambda. */
        internal val Redirect = FocusRequester()

        /**
         * Convenient way to create multiple [FocusRequester] instances.
         *
         * @sample androidx.compose.ui.samples.CreateFocusRequesterRefsSample
         */
        object FocusRequesterFactory {
            operator fun component1() = FocusRequester()

            operator fun component2() = FocusRequester()

            operator fun component3() = FocusRequester()

            operator fun component4() = FocusRequester()

            operator fun component5() = FocusRequester()

            operator fun component6() = FocusRequester()

            operator fun component7() = FocusRequester()

            operator fun component8() = FocusRequester()

            operator fun component9() = FocusRequester()

            operator fun component10() = FocusRequester()

            operator fun component11() = FocusRequester()

            operator fun component12() = FocusRequester()

            operator fun component13() = FocusRequester()

            operator fun component14() = FocusRequester()

            operator fun component15() = FocusRequester()

            operator fun component16() = FocusRequester()
        }

        /**
         * Convenient way to create multiple [FocusRequester]s, which can to be used to request
         * focus, or to specify a focus traversal order.
         *
         * @sample androidx.compose.ui.samples.CreateFocusRequesterRefsSample
         */
        fun createRefs(): FocusRequesterFactory = FocusRequesterFactory
    }

    /**
     * This function searches down the hierarchy and calls [onFound] for all focus nodes associated
     * with this [FocusRequester].
     *
     * @param onFound the callback that is run when the child is found.
     * @return false if no focus nodes were found or if the FocusRequester is
     *   [FocusRequester.Cancel]. Returns null if the FocusRequester is [FocusRequester.Default].
     *   Otherwise returns a logical or of the result of calling [onFound] for each focus node
     *   associated with this [FocusRequester].
     */
    private inline fun findFocusTarget(onFound: (FocusTargetNode) -> Boolean): Boolean {
        check(this !== Default) { InvalidFocusRequesterInvocation }
        check(this !== Cancel) { InvalidFocusRequesterInvocation }
        if (focusRequesterNodes.isEmpty()) {
            println("$FocusWarning: $FocusRequesterNotInitialized")
            return false
        }
        var success = false
        focusRequesterNodes.forEach { node ->
            node.visitChildren(Nodes.FocusTarget) {
                if (onFound(it)) {
                    success = true
                    return@forEach
                }
            }
        }
        return success
    }
}