ImageCompressor

ImageCompressor is a non-visible MIT App Inventor extension written in Java that enables on-device image compression in JPEG, PNG, and WebP formats.

Overview

ImageCompressor is a non-visible MIT App Inventor extension written in Java that enables on-device image compression in JPEG, PNG, and WebP formats. Designed for advanced developers, it provides high-performance, background-threaded processing, URI-to-path conversion, automatic naming, and event-driven callbacks to integrate seamlessly into complex App Inventor projects.

Features

• Multi-format Support: Compress to JPEG, PNG, WebP (lossy).
• Adjustable Quality: Set compression level from 0 (max compression) to 100 (best quality).
• Automatic File Management: Creates a CompressedImages folder in external storage, resolves name collisions by appending incremental suffixes.
• URI-to-File Conversion: Accepts both content URIs and direct file paths.
• Event Callbacks: ImageSelected, ImageSaved, ErrorOccurred events for responsive, block-driven workflows.
• Background Processing: Runs compression in a separate thread to maintain UI responsiveness.
• Optional Logging: Enable detailed Logcat output via LogEnabled(true).

Installation

1. Download AIX: Copy com.bosonshiggs.imagecompressor.aix from the out/ directory.
2. Add to App Inventor: In your App Inventor project, import the extension file (.aix).
3. Set Permissions: Ensure WRITE_EXTERNAL_STORAGE and READ_EXTERNAL_STORAGE permissions are granted in the packaged APK.

Usage

Block Interface

// Initialize and enable logging
ImageCompressor1.LogEnabled(true)

// Trigger image picker (use ActivityStarter or similar)
... when ButtonPick clicked do
    call ActivityStarter1.StartActivity
end

// Handle selection
when ActivityStarter1.AfterActivity do
    call ImageCompressor1.PathFromUri(ActivityStarter1.ResultUri)
end

// Compress the chosen image
when ImageCompressor1.ImageSelected(path) do
    call ImageCompressor1.CompressImage(
        path,
        "compressed_photo",
        75,
        1001
    )
end

// Receive compressed file path
when ImageCompressor1.ImageSaved(id, savedPath) do
    // id = 1001, savedPath = "/storage/.../CompressedImages/compressed_photo.jpg"
    call Notifier1.ShowAlert("Saved to: " & savedPath)
end

// Handle errors
when ImageCompressor1.ErrorOccurred(errorMsg) do
    call Notifier1.ShowAlert("Compression error: " & errorMsg)
end

Java API Reference

If you extend or inspect the .java source, the primary entry points are:

// Enable or disable debug logging
imageCompressor.LogEnabled(true);

// Convert URI to file path
String path = imageCompressor.PathFromUri(uriString);

// Compress on background thread
imageCompressor.CompressImage(
    "/storage/.../photo.png",
    "outputName",
    90,
    42 // developer-defined ID
);

// Implement callbacks in ActivityResultListener
@Override
public void resultReturned(int requestCode, int resultCode, Intent data) {
    if (resultCode == Activity.RESULT_OK) {
        Uri uri = data.getData();
        String path = imageCompressor.PathFromUri(uri.toString());
        imageCompressor.ImageSelected(path);
    }
}

// Events dispatched back to blocks
public void ImageSelected(String imagePath) { /* ... */ }
public void ImageSaved(int id, String filePath) { /* ... */ }
public void ErrorOccurred(String errorMessage) { /* ... */ }

Customization

• Directory Name: Modify myDirName constant in ImageCompressor.java.
• Supported Formats: Add support for other Bitmap.CompressFormat types as needed.
• Threading: Replace new Thread(...) with your own ExecutorService for advanced concurrency control.

Development & Build

Clone the repository and use Fast CLI to build:

git clone git@github.com:iagolirapasssos/ImageCompressor.git
cd ImageCompressor/image-compressor
fast build -o

Artifacts:

• out/com.bosonshiggs.imagecompressor.aix — extension file.
• docs/ — generated Javadoc and usage markdown.

Contributing

1. Fork the repository.
2. Create a feature branch: git checkout -b feature/my-extension-update.
3. Commit your changes with tests.
4. Build and verify with fast build -o.
5. Open a Pull Request describing your enhancements.

License

This project is licensed under the MIT License. See LICENSE for details.

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For more information, visit the App Inventor community.