Android 为卡片的上半部分添加一个边框，用圆角半径组合

边框似乎不允许打开的形状，强制形状关闭，即使你画了3条线，因为你需要使用Modifier.draBehind或Modifier.draWithContent.

创建了一个Modifier，将U形边框绘制为

fun Modifier.semiBorder(strokeWidth: Dp, color: Color, cornerRadiusDp: Dp) = composed(
    factory = {
        val density = LocalDensity.current
        val strokeWidthPx = density.run { strokeWidth.toPx() }
        val cornerRadius = density.run { cornerRadiusDp.toPx() }

        Modifier.drawBehind {
            val width = size.width
            val height = size.height

            drawLine(
                color = color,
                start = Offset(x = 0f, y = height),
                end = Offset(x = 0f, y = cornerRadius),
                strokeWidth = strokeWidthPx
            )

            // Top left arc
            drawArc(
                color = color,
                startAngle = 180f,
                sweepAngle = 90f,
                useCenter = false,
                topLeft = Offset.Zero,
                size = Size(cornerRadius * 2, cornerRadius * 2),
                style = Stroke(width = strokeWidthPx)
            )


            drawLine(
                color = color,
                start = Offset(x = cornerRadius, y = 0f),
                end = Offset(x = width - cornerRadius, y = 0f),
                strokeWidth = strokeWidthPx
            )

            // Top right arc
            drawArc(
                color = color,
                startAngle = 270f,
                sweepAngle = 90f,
                useCenter = false,
                topLeft = Offset(x = width - cornerRadius * 2, y = 0f),
                size = Size(cornerRadius * 2, cornerRadius * 2),
                style = Stroke(width = strokeWidthPx)
            )

            drawLine(
                color = color,
                start = Offset(x = width, y = height),
                end = Offset(x = width, y = cornerRadius),
                strokeWidth = strokeWidthPx
            )
        }
    }
)

用法

@Composable
private fun UShapeBorderSample() {
    Card(
        shape = RoundedCornerShape(
            topEnd = 10.dp,
            topStart = 10.dp,
            bottomEnd = 0.dp,
            bottomStart = 0.dp
        ),
        modifier = Modifier
            .semiBorder(1.dp, Color.Black, 10.dp)

    ) {
        Box(
            modifier = Modifier
                .size(150.dp)
                .background(Color.White),
            contentAlignment = Alignment.Center
        ) {
            Text("Hello World")
        }
    }

    Spacer(modifier = Modifier.height(10.dp))

    Card(
        shape = RoundedCornerShape(
            topEnd = 20.dp,
            topStart = 20.dp,
            bottomEnd = 0.dp,
            bottomStart = 0.dp
        ),
        modifier = Modifier
            .semiBorder(1.dp, Color.Black, 20.dp)

    ) {
        Box(
            modifier = Modifier
                .size(150.dp)
                .background(Color.White),
            contentAlignment = Alignment.Center
        ) {
            Text("Hello World")
        }
    }
}

您需要使用圆弧来创建圆角.在创建形状时，不是传递厚度，而是传递形状半径.绘制边框时需要厚度.您绘制的是一个宽度为1.dp的矩形.

@Composable
private fun createShape(cornerRadius: Dp): Shape {

    val density = LocalDensity.current
    return GenericShape { size, _ ->

        val width = size.width
        val height = size.height
        val cornerRadiusPx = density.run { cornerRadius.toPx() }

        moveTo(0f, height)

        // Vertical line on left size
        lineTo(0f, cornerRadiusPx * 2)

        arcTo(
            rect = Rect(
                offset = Offset.Zero,
                size = Size(cornerRadiusPx * 2, cornerRadiusPx * 2)
            ),
            startAngleDegrees = 180f,
            sweepAngleDegrees = 90f,
            forceMoveTo = false
        )

        lineTo(width - cornerRadiusPx * 2, 0f)
        arcTo(
            rect = Rect(
                offset = Offset(width - cornerRadiusPx * 2, 0f),
                size = Size(cornerRadiusPx * 2, cornerRadiusPx * 2)
            ),
            startAngleDegrees = 270f,
            sweepAngleDegrees = 90f,
            forceMoveTo = false
        )
        // Vertical line on right size
        lineTo(width, height)

    }
}

用法

@Composable
private fun UShapeBorderSample() {
    Card(
        shape = RoundedCornerShape(
            topEnd = 10.dp,
            topStart = 10.dp,
            bottomEnd = 0.dp,
            bottomStart = 0.dp
        ),
        modifier = Modifier
            .border(BorderStroke(width = 1.dp, color = Color.Black), createShape(10.dp))

    ) {
        Box(modifier = Modifier
            .size(200.dp)
            .background(Color.White),
            contentAlignment = Alignment.Center
        ) {
            Text("Hello World")
        }
    }
}

边框不尊重形状，因为它是一幅图，但Card是引擎盖下的Box，它使用Shape，Modifier.clip()本身就是Modifier.graphicsLayer{clip}，它在一个层上应用操作.

您可以查看关于剪辑和边框的不同之处的答案.

https://stackoverflow.com/a/73091667/5457853个