有没有办法序列化/反序列化jetpack组成画布路径？

Question

我创建了一个画布应用程序。用户可以在画布上绘图。现在我想将其绘制进度保存在房间数据库中。但我收到 androidx.compose.ui.graphics.Path 的序列化/反序列化错误。

这是我的实体序列化/反序列化代码：

@Entity(tableName = "canvas_projects")
data class CanvasProject(
    @PrimaryKey(autoGenerate = true) val id: Long = 0,
    val name: String,
    val ratio: Float,
    @TypeConverters(BitmapConverter::class) val canvasBackground: Bitmap?,
    @TypeConverters(PathListConverter::class) val paths: List<PathWithProperties>
)

data class PathWithProperties(
    @TypeConverters(PathConverter::class) val path: Path,
    val pathProperties: PathProperties
)

object PathConverter {
    private val gson = Gson()
    @TypeConverter
    fun fromPath(path: Path) : String {
        return gson.toJson(path)
    }

    @TypeConverter
    fun toPath(data: String) : Path {
        return gson.fromJson(data, Path::class.java)
    }
}

data class PathProperties(
    val strokeWidth: Float,
    val color: String,
    val alphas: Float,
    val strokeCap: StrokeCap = StrokeCap.Round,
    val strokeJoin: StrokeJoin = StrokeJoin.Round,
    val eraseMode: Boolean,
    val isBitmap: Boolean,
    val bitmap: ImageBitmap? = null,
    val bitmapRect: Rect? = null
)

object BitmapConverter {
    @TypeConverter
    fun fromBitmap(bitmap: Bitmap?): ByteArray? {
        if (bitmap != null) {
            val outputStream = ByteArrayOutputStream()
            bitmap.compress(Bitmap.CompressFormat.PNG, 100, outputStream)
            return outputStream.toByteArray()
        } else return null
    }

    @TypeConverter
    fun toBitmap(byteArray: ByteArray?): Bitmap? {
        return if (byteArray != null) BitmapFactory.decodeByteArray(byteArray, 0, byteArray.size) else null
    }
}

object PathListConverter {
    private val gson = Gson()

    @TypeConverter
    fun fromPathList(pathList: List<PathWithProperties>): String {
        return gson.toJson(pathList)
    }

    @TypeConverter
    fun toPathList(data: String): List<PathWithProperties> {
        val listType = object : TypeToken<List<PathWithProperties>>() {}.type
        return gson.fromJson(data, listType)
    }
}

但是我收到以下错误：

com.google.gson.JsonIOException：接口无法实例化！为此类型注册 InstanceCreator 或 TypeAdapter。接口名称：androidx.compose.ui.graphics.Path

如何解决这个问题？

Answer 1

您无法序列化

androidx.compose.ui.graphics.Path

，但您可以创建一个类，例如

SaveablePath

，它包含或是一个路径，并在接口或用例中定义诸如

moveTo(x, y)

、

lineTo(x, y)

之类的操作

并对它们进行序列化和反序列化，例如

PathDrawEntity(operationType, x, y, other serializable/parcelable properties)

当您使用路径对象从数据库读取数据时，使用此类来提取所有内容

class SaveablePath(
    va saveUseCase: SaveUseCase,
):Path {

    override fun moveTo(x: Float, y: Float) {
        internalPath.moveTo(x, y)
         saveUseCase.moveTo(x,y)
    }

    // Do samething with others
    override fun relativeMoveTo(dx: Float, dy: Float) {
        internalPath.rMoveTo(dx, dy)
    }

    override fun lineTo(x: Float, y: Float) {
        internalPath.lineTo(x, y)
    }

    override fun relativeLineTo(dx: Float, dy: Float) {
        internalPath.rLineTo(dx, dy)
    }

    override fun quadraticBezierTo(x1: Float, y1: Float, x2: Float, y2: Float) {
        internalPath.quadTo(x1, y1, x2, y2)
    }

    override fun quadraticTo(x1: Float, y1: Float, x2: Float, y2: Float) {
        internalPath.quadTo(x1, y1, x2, y2)
    }

    override fun relativeQuadraticBezierTo(dx1: Float, dy1: Float, dx2: Float, dy2: Float) {
        internalPath.rQuadTo(dx1, dy1, dx2, dy2)
    }
}

还有一个函数，用于读取保存的操作，并在读取时将其应用到 Path 以在 Canvas 上绘制。