Question

每当我为 myMatrix 分配一个新的 Matrix 时，myMatrix 的引用都不会改变。结果，没有重新组合。

任何人都知道如何为 myMatrix 分配新的引用，或者以不同的方式解决这个问题？

@Composable
fun MatrixTest(){
    var myMatrix by remember { mutableStateOf(Matrix()) }

    Box(
        Modifier
            .graphicsLayer {
                translationX = myMatrix.values[Matrix.TranslateX]
                translationY = myMatrix.values[Matrix.TranslateY]
            }
            .border(2.dp, Color.Black)
            .size(100.dp)
            .pointerInput(Unit, myMatrix) {
                detectTransformGestures { centroid, pan, zoom, rotation ->
                    myMatrix.translate(pan.x, pan.y)

                    myMatrix = Matrix(myMatrix.values)
                }
            }
    )
}

Answer 1

对 mutableStateOf 使用不同的平等政策是一种解决方案。在本例中，我使用了 neverEqualPolicy，它将值的任何设置都视为更改。

参考：

/**
 * A policy never treat values of a [MutableState] as equivalent.
 *
 * Setting [MutableState.value] will always be considered a change. When applying a
 * [MutableSnapshot] that changes the state will always conflict with other snapshots that change
 * the same state.
 */
@Suppress("UNCHECKED_CAST")
fun <T> neverEqualPolicy(): SnapshotMutationPolicy<T> =
    NeverEqualPolicy as SnapshotMutationPolicy<T>

代码：

@Composable
fun TestMatrix(){
    var myMatrix by remember { mutableStateOf(Matrix(), neverEqualPolicy()) }

    Box(
        Modifier
            .graphicsLayer {
                translationX = myMatrix.values[Matrix.TranslateX]
                translationY = myMatrix.values[Matrix.TranslateY]
            }
            .border(2.dp, Color.Black)
            .size(100.dp)
            .pointerInput(Unit, myMatrix) {
                detectTransformGestures { centroid, pan, zoom, rotation ->
                    myMatrix.translate(pan.x, pan.y)

                    myMatrix = Matrix(myMatrix.values)
                }
            }
    )
}

矩阵不更新

1 个答案: