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.ui.ExperimentalComposeUiApi
import androidx.compose.ui.Modifier
import androidx.compose.ui.node.ModifierNodeElement
import androidx.compose.ui.platform.InspectorInfo
/**
* 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 = this then FocusChangedElement(onFocusChanged)
@OptIn(ExperimentalComposeUiApi::class)
private data class FocusChangedElement(
val onFocusChanged: (FocusState) -> Unit
) : ModifierNodeElement<FocusChangedModifierNode>() {
override fun create() = FocusChangedModifierNode(onFocusChanged)
override fun update(node: FocusChangedModifierNode) = node.apply {
onFocusChanged = this@FocusChangedElement.onFocusChanged
}
override fun InspectorInfo.inspectableProperties() {
name = "onFocusChanged"
properties["onFocusChanged"] = onFocusChanged
}
}
@ExperimentalComposeUiApi
private class FocusChangedModifierNode(
var onFocusChanged: (FocusState) -> Unit
) : FocusEventModifierNode, Modifier.Node() {
private var focusState: FocusState? = null
override fun onFocusEvent(focusState: FocusState) {
if (this.focusState != focusState) {
this.focusState = focusState
this.onFocusChanged.invoke(focusState)
}
}
}