Transition.kt
/*
* Copyright (C) 2022 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.constraintlayout.compose
import android.annotation.SuppressLint
import android.util.Log
import androidx.compose.runtime.Composable
import androidx.compose.runtime.Immutable
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.ui.platform.LocalDensity
import androidx.compose.ui.unit.dp
import androidx.constraintlayout.core.parser.CLObject
import androidx.constraintlayout.core.parser.CLParser
import androidx.constraintlayout.core.parser.CLParsingException
import androidx.constraintlayout.core.state.CorePixelDp
import androidx.constraintlayout.core.state.TransitionParser
import org.intellij.lang.annotations.Language
/**
* Defines interpolation parameters between two [ConstraintSet]s.
*/
@Immutable
interface Transition {
fun getStartConstraintSetId(): String
fun getEndConstraintSetId(): String
}
/**
* Parses the given JSON5 into a [Transition].
*
* See the official [Github Wiki](https://github.com/androidx/constraintlayout/wiki/Compose-MotionLayout-JSON-Syntax#transitions) to learn the syntax.
*/
@SuppressLint("ComposableNaming")
@Composable
fun Transition(@Language("json5") content: String): Transition? {
val dpToPixel = with(LocalDensity.current) { 1.dp.toPx() }
val transition = remember(content) {
val parsed = try {
CLParser.parse(content)
} catch (e: CLParsingException) {
Log.e("CML", "Error parsing JSON $e")
null
}
mutableStateOf(
if (parsed != null) {
val pixelDp = CorePixelDp { dpValue -> dpValue * dpToPixel }
TransitionImpl(parsed, pixelDp)
} else {
null
}
)
}
return transition.value
}
/**
* Subclass of [Transition] for internal use.
*
* Used to reduced the exposed API from [Transition].
*/
internal class TransitionImpl(
private val parsedTransition: CLObject,
private val pixelDp: CorePixelDp
) : Transition {
/**
* Applies all Transition properties to [transition].
*/
fun applyAllTo(transition: androidx.constraintlayout.core.state.Transition, type: Int) {
try {
TransitionParser.parse(parsedTransition, transition, pixelDp)
} catch (e: CLParsingException) {
Log.e("CML", "Error parsing JSON $e")
}
}
/**
* Applies only the KeyFrame related properties (KeyCycles, KeyAttributes, KeyPositions) to
* [transition], which effectively sets the respective parameters for each WidgetState.
*/
fun applyKeyFramesTo(transition: androidx.constraintlayout.core.state.Transition) {
try {
TransitionParser.parseKeyFrames(parsedTransition, transition)
} catch (e: CLParsingException) {
Log.e("CML", "Error parsing JSON $e")
}
}
override fun getStartConstraintSetId(): String {
return parsedTransition.getStringOrNull("from") ?: "start"
}
override fun getEndConstraintSetId(): String {
return parsedTransition.getStringOrNull("to") ?: "end"
}
}