FocusChangedModifier.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.MutableState
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.compose.ui.composed
import androidx.compose.ui.platform.debugInspectorInfo

/**
 * Add this modifier to a component to observe focus state events. [onFocusChanged] is invoked
 * when the focus state changes. The [onFocusChanged] modifier listens to the state of the first
 * [focusTarget] following this modifier.
 *
 * @sample androidx.compose.ui.samples.FocusableSample
 *
 * Note: If you want to be notified every time the internal focus state is written to (even if it
 * hasn't changed), use [onFocusEvent] instead.
 */
fun Modifier.onFocusChanged(onFocusChanged: (FocusState) -> Unit): Modifier =
    composed(
        inspectorInfo = debugInspectorInfo {
            name = "onFocusChanged"
            properties["onFocusChanged"] = onFocusChanged
        }
    ) {
        val focusState: MutableState<FocusState?> = remember { mutableStateOf(null) }
        Modifier.onFocusEvent {
            if (focusState.value != it) {
                focusState.value = it
                onFocusChanged(it)
            }
        }
    }