1 /*
2  * Copyright 2023 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package androidx.compose.foundation.lazy.layout
18 
19 import androidx.compose.ui.layout.LayoutCoordinates
20 import androidx.compose.ui.layout.OnGloballyPositionedModifier
21 import androidx.compose.ui.util.fastForEach
22 import kotlin.coroutines.Continuation
23 import kotlin.coroutines.resume
24 import kotlinx.coroutines.suspendCancellableCoroutine
25 
26 /**
27  * Internal modifier which allows to delay some interactions (e.g. scroll) until layout is ready.
28  */
29 internal class AwaitFirstLayoutModifier : OnGloballyPositionedModifier {
30     private var wasPositioned = false
31     private val continuations = mutableListOf<Continuation<Unit>>()
32 
waitForFirstLayoutnull33     suspend fun waitForFirstLayout() {
34         if (!wasPositioned) {
35             var continuation: Continuation<Unit>? = null
36             try {
37                 suspendCancellableCoroutine<Unit> {
38                     continuation = it
39                     continuations.add(it)
40                 }
41             } finally {
42                 continuations.remove(continuation)
43             }
44         }
45     }
46 
onGloballyPositionednull47     override fun onGloballyPositioned(coordinates: LayoutCoordinates) {
48         if (!wasPositioned) {
49             wasPositioned = true
50             continuations.fastForEach { it.resume(Unit) }
51             continuations.clear()
52         }
53     }
54 }
55