android - Jetpack Compose 中的可扩展文本

Question

所以我正在使用这样的Text()组合：

Text(
    text = "this is some sample text that is long and so it is 
            ellipsized",
    maxLines = 1,
    overflow = TextOverflow.Ellipsis
)

并且它正确地省略了文本：

问题是我想See More在省略号末尾添加一个标签，提示用户展开可见文本框。我将如何添加它？

标签： androidkotlinandroid-jetpack-composeandroid-jetpack-compose-text

Answer 1

要解决这个问题，您需要使用onTextLayoutget TextLayoutResult：它包含有关绘制文本状态的所有信息。

让它适用于多行是一项棘手的任务。为此，您需要计算椭圆文本和“...查看更多”文本的大小，然后，当您拥有这两个值时，您需要计算需要删除多少文本，以便“...查看更多”非常适合在行尾：

@Composable
fun ExpandableText(
    text: String,
    modifier: Modifier = Modifier,
    minimizedMaxLines: Int = 1,
) {
    var cutText by remember(text) { mutableStateOf<String?>(null) }
    var expanded by remember { mutableStateOf(false) }
    val textLayoutResultState = remember { mutableStateOf<TextLayoutResult?>(null) }
    val seeMoreSizeState = remember { mutableStateOf<IntSize?>(null) }
    val seeMoreOffsetState = remember { mutableStateOf<Offset?>(null) }

    // getting raw values for smart cast
    val textLayoutResult = textLayoutResultState.value
    val seeMoreSize = seeMoreSizeState.value
    val seeMoreOffset = seeMoreOffsetState.value

    LaunchedEffect(text, expanded, textLayoutResult, seeMoreSize) {
        val lastLineIndex = minimizedMaxLines - 1
        if (!expanded && textLayoutResult != null && seeMoreSize != null
            && lastLineIndex + 1 == textLayoutResult.lineCount
            && textLayoutResult.isLineEllipsized(lastLineIndex)
        ) {
            var lastCharIndex = textLayoutResult.getLineEnd(lastLineIndex, visibleEnd = true) + 1
            var charRect: Rect
            do {
                lastCharIndex -= 1
                charRect = textLayoutResult.getCursorRect(lastCharIndex)
            } while (
                charRect.left > textLayoutResult.size.width - seeMoreSize.width
            )
            seeMoreOffsetState.value = Offset(charRect.left, charRect.bottom - seeMoreSize.height)
            cutText = text.substring(startIndex = 0, endIndex = lastCharIndex)
        }
    }
    
    Box(modifier) {
        Text(
            text = cutText ?: text,
            maxLines = if (expanded) Int.MAX_VALUE else minimizedMaxLines,
            overflow = TextOverflow.Ellipsis,
            onTextLayout = { textLayoutResultState.value = it },
        )
        if (!expanded) {
            val density = LocalDensity.current
            Text(
                "... See more",
                onTextLayout = { seeMoreSizeState.value = it.size },
                modifier = Modifier
                    .then(
                        if (seeMoreOffset != null)
                            Modifier.offset(
                                x = with(density) { seeMoreOffset.x.toDp() },
                                y = with(density) { seeMoreOffset.y.toDp() },
                            )
                        else
                            Modifier
                    )
                    .clickable {
                        expanded = true
                        cutText = null
                    }
                    .alpha(if (seeMoreOffset != null) 1f else 0f)
            )
        }
    }
}