如何在 Jetpack Compose 中将图像 URL 设置为 Coil 上的错误占位符

Question

Coil 接受可绘制资源作为错误占位符。有没有办法在这里使用图像 URL 来代替？

这是我正在处理的代码：

// Global variables
var currentlySelectedImageUri = mutableStateOf<Uri?>(null)
var previousImageUri: Uri? = null

// @Composable fun() {...
Image(
    painter = rememberImagePainter(
    if (currentlySelectedImageUri.value != null) { // use the currently selected image
        currentlySelectedImageUri.value
    } else {
        if (previousImageUri != null) { // use the previously selected image
            previousImageUri
        } else {
            R.drawable.blank_profile_picture // use the placeholder image
        }
    }, builder = {
        placeholder(R.drawable.blank_profile_picture)
        error(R.drawable.blank_profile_picture) // FIXME: Set the previously selected image
    }),
    contentDescription = "profile image",
    contentScale = ContentScale.Crop,
    modifier = Modifier.fillMaxWidth()
)

Answer 1

在 Coil 2.0.0中， 和AsyncImage都rememberAsyncImagePainter具有error接受任何其他画家的参数：

AsyncImage(
    model = imageURL,
    contentDescription = null,
    error = painterResource(R.drawable.error)
)

线圈1.4.0版本：

您可以检查painter.state值。

最初它是ImagePainter.State.Empty，当图像加载时它是ImagePainter.State.Loading，如果失败 - 它会变成ImagePainter.State.Error。此时，您可以更改线圈 url，例如，使用本地记住变量：

AsyncImage(
    model = imageURL,
    contentDescription = null,
    error = painterResource(R.drawable.error)
)