Compose 小说 app 1

记录一下写小说阅读器过程中遇到的一些问题及解决方案。
首先第一个问题就是小说的分页。

如何分页

这里可以通过 ViewPager 来进行分页，但是 Compose 中并没有 ViewPager，经过我的寻找，找到了一个 Compose 中的 ViewPager，是 google 出的一个库。
https://google.github.io/accompanist/pager/

接下来就是第二个问题，如何确定一页的大小。也就是确定一页能够显示的字数。

确定一页能够显示的字数

这个也比较困难，因为 Compose 中的 Text 并没有暴露出太多的 api，所以也是比较困难的，最终在 https://my.oschina.net/gotax/blog/136860 这篇文章的启发下找到了解决办法。

@ExperimentalPagerApi
@Preview
@Composable
fun PageTest() {
    Box(
        modifier = Modifier
            .fillMaxSize()
    ) {
        val pageState = rememberPagerState(pageCount = 100, infiniteLoop = true)
        HorizontalPager(
            state = pageState,
            modifier = Modifier.fillMaxHeight(),
            verticalAlignment = Alignment.Top,
            horizontalAlignment = Alignment.Start
        ) { state ->
            Box(
                modifier = Modifier
                    .fillMaxSize()
                    .graphicsLayer {
                        // Calculate the absolute offset for the current page from the
                        // scroll position. We use the absolute value which allows us to mirror
                        // any effects for both directions
                        val pageOffset = calculateCurrentOffsetForPage(state).absoluteValue

                        // We animate the scaleX + scaleY, between 85% and 100%
                        lerp(
                            start = 0.85f,
                            stop = 1f,
                            fraction = 1f - pageOffset.coerceIn(0f, 1f)
                        ).also { scale ->
                            scaleX = scale
                            scaleY = scale
                        }

                        // We animate the alpha, between 50% and 100%
                        alpha = lerp(
                            start = 0.5f,
                            stop = 1f,
                            fraction = 1f - pageOffset.coerceIn(0f, 1f)
                        )
                    }
            ) {
                Column {
                    val sb = StringBuilder()
                    repeat(state * 10) {
                        sb.append("阿a达")
                    }
                    var totalNumState by remember {
                        mutableStateOf(0)
                    }
                    Text(
                        text = "Page: $state current page = ${pageState.currentPage}",
                    )
                    Text(text = "$totalNumState")
                    Text(
                        onTextLayout = {
                            try {
                                val lineNum =
                                    it.getLineForVerticalPosition(it.size.height.toFloat())
                                if (lineNum != 0) {
                                    val totalNum = it.getLineEnd(lineNum, false)
                                    Log.d(
                                        "PageTest",
                                        "line Number = $lineNum, line end totalNum = $totalNum str = ${sb.toString().length}"
                                    )
                                    totalNumState = totalNum
                                }
                            } catch (e: Exception) {
                                e.printStackTrace()
                            }
                        },
                        text = sb.toString()

                    )
                }
            }
        }
    }
}