如何在 Jetpack Compose 中使用 Coil 显示自定义可组合占位符？

Question

我需要使用 Coil 在 Jetpack Compose 中显示自定义占位符，但该占位符不是可绘制的，而是我自定义的可组合函数。用线圈可以做到这一点吗？这是我使用线圈的代码片段：

Image(
    modifier = Modifier
        .size(120.dp)
        .align(Alignment.CenterHorizontally),
    painter = rememberImagePainter(
        data = entry.imageUrl,
        builder = {
            crossfade(true)
            MyPlaceholder(resourceId = R.drawable.ic_video)
        },
    ),
    contentDescription = entry.pokemonName
)

这是我的自定义占位符撰写功能：

@Composable
fun MyPlaceholder(@DrawableRes resourceId: Int) {
    Surface(
        modifier = Modifier.fillMaxSize(),
        color = Color(0xFFE0E0E0)
    ) {
        Box(
            modifier = Modifier.fillMaxSize(),
            contentAlignment = Alignment.Center,
        ) {
            Surface(
                modifier = Modifier.size(30.dp),
                shape = CircleShape,
                color = Color.White
            ) {
                Image(
                    modifier = Modifier
                        .padding(
                            PaddingValues(
                                start = 11.25.dp,
                                top = 9.25.dp,
                                end = 9.25.dp,
                                bottom = 9.25.dp
                            )
                        )
                        .fillMaxSize(),
                    painter = painterResource(id = resourceId),
                    contentDescription = null
                )
            }
        }
    }
}

我的等级（线圈）：

// Coil
implementation 'io.coil-kt:coil-compose:1.4.0'

Answer 1

Coil 没有对可组合占位符的内置支持。

您可以将可组合项放入其中并根据状态Box显示占位符。Image

在我的示例中，如果状态是Loading或 ，我会显示它Error。您可以为案例添加另一个视图参数Error并使用Crossfade代替AnimatedVisibility。

此外，我还添加Modifier.matchParentSize()了Image根据修饰符参数计算出的父级大小。您不能将修饰符参数直接传递给Image，因为修饰符仅适用align于直接子级，这就是为什么您始终必须将其传递给容器视图。

@Composable
fun Image(
    painter: ImagePainter,
    placeholder: @Composable () -> Unit,
    contentDescription: String?,
    modifier: Modifier = Modifier,
    alignment: Alignment = Alignment.Center,
    contentScale: ContentScale = ContentScale.Fit,
    alpha: Float = DefaultAlpha,
    colorFilter: ColorFilter? = null,
) {
    Box(modifier) {
        Image(
            painter = painter,
            contentDescription = contentDescription,
            alignment = alignment,
            contentScale = contentScale,
            alpha = alpha,
            colorFilter = colorFilter,
            modifier = Modifier.matchParentSize()
        )

        AnimatedVisibility(
            visible = when (painter.state) {
                is ImagePainter.State.Empty,
                is ImagePainter.State.Success,
                -> false
                is ImagePainter.State.Loading,
                is ImagePainter.State.Error,
                -> true
            }
        ) {
            placeholder()
        }
    }
}

用法：

Image(
    painter = rememberImagePainter(imageUrl),
    placeholder = {
        CustomComposableView(...)
    },
    contentDescription = "...",
    modifier = Modifier
        ...
)