Coil 3

Load and display images from PlatformFile using Coil

Supported on Android, iOS, macOS, JVM, JS and WASM targets

Introduction

FileKit provides seamless integration with Coil, a popular image loading library for Kotlin Multiplatform. This integration allows you to easily load and display images from PlatformFile objects using Coil’s powerful image loading capabilities.

Configuration

Add the FileKit Coil dependency to your project:

build.gradle.kts

implementation("io.github.vinceglb:filekit-coil:0.12.0")

Then, configure Coil in your app’s root composable:

@Composable
fun App() {
    setSingletonImageLoaderFactory { context ->
        ImageLoader.Builder(context)
            .components {
                addPlatformFileSupport()
            }
            .build()
    }

    MaterialTheme {
        // Your app content
    }
}

This setup utilizes the addPlatformFileSupport() extension function to register the necessary components within Coil’s pipeline, enabling it to handle PlatformFile objects:

• PlatformFileMapper: Maps the PlatformFile object to a data type that Coil’s fetchers can understand.
• PlatformFileFetcher: Handles the actual loading of the image data from the PlatformFile.
• PlatformFileKeyer: Generates stable cache keys for PlatformFile objects, allowing Coil to effectively cache the loaded images.

Usage

Once configured, you can use Coil’s standard AsyncImage composable with PlatformFile objects:

@Composable
fun ImagePreview(file: PlatformFile) {
    AsyncImage(
        model = file,
        contentDescription = "Image preview",
        modifier = Modifier.fillMaxWidth()
    )
}

For more information about using Coil’s image loading capabilities, refer to the official Coil documentation.

Handling Security-Scoped Resources (iOS/macOS)

On iOS and macOS, if you obtain a PlatformFile through mechanisms like the document picker, your app gets temporary, scoped access permission. To ensure Coil can load the image data while this permission is active, FileKit provides the securelyAccessFile extension function for AsyncImagePainter.State.

Use this function within the onState callback of AsyncImage:

@Composable
fun ImagePreviewScoped(file: PlatformFile) {
    AsyncImage(
        model = file,
        contentDescription = "Image preview",
        modifier = Modifier.fillMaxWidth(),
        onState = { state ->
            // Start/stop security-scoped access based on Coil's state
            state.securelyAccessFile(file)
        }
    )
}

This function automatically calls startAccessingSecurityScopedResource() when Coil starts loading (State.Loading) and stopAccessingSecurityScopedResource() when it finishes (State.Success or State.Error), ensuring the file remains accessible throughout the loading process.

Example

Here’s a complete example showing how to use the Coil integration in a gallery:

@Composable
fun App() {
    setSingletonImageLoaderFactory { context ->
        ImageLoader.Builder(context)
            .components {
                addPlatformFileSupport()
            }
            .build()
    }

    MaterialTheme {
        ImageGallery()
    }
}

@Composable
fun ImageGallery(files: List<PlatformFile>) {
    LazyColumn {
        items(files) { file ->
            AsyncImage(
                model = file,
                contentDescription = "Gallery image",
                modifier = Modifier
                    .fillMaxWidth()
                    .height(200.dp),
                contentScale = ContentScale.Crop
            )
        }
    }
}

Next steps

PlatformFile

Learn more about the core file representation used by FileKit.

Image Utils

Discover more image manipulation utilities provided by FileKit.