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android - Jetpack compose - 在文本后面绘制背景

问题描述

我想AnnotatedString在 Jetpack Compose 中绘制一些背景（此处为示例）。使用视图系统，我们可以通过编写自定义文本视图来做到这一点 - https://medium.com/androiddevelopers/drawing-a-rounded-corner-background-on-text-5a610a95af5。有没有办法使用 Jetpack Compose 做到这一点？

我正在查看draw修饰符，Text但我似乎无法弄清楚如何获取行号或我需要在其上绘制背景的文本的开始/结束。

我应该使用Canvas而不是Text吗？

标签： androidandroid-jetpack-composeandroid-jetpack-compose-text

解决方案

Text字符布局信息的主要来源是TextLayoutResult可以通过onTextLayout参数接收

它的 API 远非完美。getPathForRange返回Path这正是您所需要的，但与其他任何东西一样，Path它不能被修改，例如，您将无法绕过这条路径的拐角，与普通SpanStyle背景没有太大区别

那里getBoundingBox只返回一个字符的帧。我玩了一下，得到Rect了选定范围的 s 列表：

fun TextLayoutResult.getBoundingBoxesForRange(start: Int, end: Int): List<Rect> {
    var prevRect: Rect? = null
    var firstLineCharRect: Rect? = null
    val boundingBoxes = mutableListOf<Rect>()
    for (i in start..end) {
        val rect = getBoundingBox(i)
        val isLastRect = i == end
        
        // single char case
        if (isLastRect && firstLineCharRect == null) {
            firstLineCharRect = rect
            prevRect = rect
        }

        // `rect.right` is zero for the last space in each line
        // looks like an issue to me, reported: https://issuetracker.google.com/issues/197146630
        if (!isLastRect && rect.right == 0f) continue

        if (firstLineCharRect == null) {
            firstLineCharRect = rect
        } else if (prevRect != null) {
            if (prevRect.bottom != rect.bottom || isLastRect) {
                boundingBoxes.add(
                    firstLineCharRect.copy(right = prevRect.right)
                )
                firstLineCharRect = rect
            }
        }
        prevRect = rect
    }
    return boundingBoxes
}

现在您可以在 上绘制这些矩形Canvas：

Box(Modifier.padding(10.dp)) {
    val text =
        "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
    val selectedParts = listOf(
        "consectetur adipiscing",
        "officia deserunt",
        "dolore magna aliqua. Ut enim ad minim veniam, quis nostrud",
        "consequat.",
    )
    var selectedPartPaths by remember { mutableStateOf(listOf<Path>()) }
    Text(
        text,
        style = MaterialTheme.typography.h6,
        onTextLayout = { layoutResult ->
            selectedPartPaths = selectedParts.map { part ->
                val cornerRadius = CornerRadius(x = 20f, y = 20f)
                Path().apply {
                    val startIndex = text.indexOf(part)
                    val boundingBoxes = layoutResult
                        .getBoundingBoxesForRange(
                            start = startIndex,
                            end = startIndex + part.count()
                        )
                    for (i in boundingBoxes.indices) {
                        val boundingBox = boundingBoxes[i]
                        val leftCornerRoundRect =
                            if (i == 0) cornerRadius else CornerRadius.Zero
                        val rightCornerRoundRect =
                            if (i == boundingBoxes.indices.last) cornerRadius else CornerRadius.Zero
                        addRoundRect(
                            RoundRect(
                                boundingBox.inflate(verticalDelta = -2f, horizontalDelta = 7f),
                                topLeft = leftCornerRoundRect,
                                topRight = rightCornerRoundRect,
                                bottomRight = rightCornerRoundRect,
                                bottomLeft = leftCornerRoundRect,
                            )
                        )
                    }
                }
            }
        },
        modifier = Modifier.drawBehind {
            selectedPartPaths.forEach { path ->
                drawPath(path, style = Fill, color = Color.Blue.copy(alpha = 0.2f))
                drawPath(path, style = Stroke(width = 2f), color = Color.Blue)
            }
        }
    )
}

fun Rect.inflate(verticalDelta: Float, horizontalDelta: Float) =
    Rect(
        left = left - horizontalDelta,
        top = top - verticalDelta,
        right = right + horizontalDelta,
        bottom = bottom + verticalDelta,
    )

结果：

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