Callbacks

Things happen. The connection drops. The printer runs out of paper. A print job finishes. Callbacks let your app respond in real-time.

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Available Callbacks

Callback	Tells You When...
ConnectionStateCallback	Device connects, disconnects, or is connecting
PrinterStatusCallback	Printer state changes (paper out, cover open, ready)
PrintProgressCallback	Each label in a multi-label job completes
ScanCallback	A barcode is scanned (covered in Scanning Guide)

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ConnectionStateCallback

Know instantly when your connection changes:

import com.averydennison.addevicemanager.callbacks.ConnectionStateCallback;
import com.averydennison.addevicemanager.connection.DeviceConnection;
import com.averydennison.addevicemanager.connection.DeviceConnectionState;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

private final Logger logger = LoggerFactory.getLogger(getClass());

deviceAdapter.setConnectionStateCallback(new ConnectionStateCallback() {
    @Override
    public void onConnectionStateChanged(
            DeviceConnection connection,
            DeviceConnectionState newState,
            String reason) {

        switch (newState) {
            case CONNECTING:
                logger.info("Connecting to {}...", connection.getName());
                runOnUiThread(() -> showStatus("Connecting..."));
                break;

            case CONNECTED:
                logger.info("Connected to {}", connection.getName());
                runOnUiThread(() -> {
                    showStatus("Connected");
                    enablePrintButton(true);
                });
                break;

            case DISCONNECTING:
                logger.info("Disconnecting...");
                runOnUiThread(() -> showStatus("Disconnecting..."));
                break;

            case DISCONNECTED:
                logger.info("Disconnected: {}", reason);
                runOnUiThread(() -> {
                    showStatus("Disconnected");
                    enablePrintButton(false);
                    // Maybe attempt reconnection?
                    offerReconnect(reason);
                });
                break;
        }
    }
});

Connection States

State	Description
CONNECTING	Connection in progress
CONNECTED	Ready to use
DISCONNECTING	Graceful disconnect in progress
DISCONNECTED	Not connected (check reason for why)

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PrinterStatusCallback

The printer tells you when something needs attention:

import com.averydennison.addevicemanager.callbacks.PrinterStatusCallback;
import com.averydennison.addevicemanager.models.PrinterStatus;

PrinterAdapter printerAdapter = deviceAdapter.getPrinterAdapter();

printerAdapter.setPrinterStatusCallback(new PrinterStatusCallback() {
    @Override
    public void onPrinterStatusChanged(PrinterStatus status) {
        logger.info("Printer status: {}", status.getDescription());
        
        // React based on code
        if ("NORMAL".equalsIgnoreCase(status.rawCode)) {
            // Printer is ready — enable print button
        } else if ("PAPER_JAM".equalsIgnoreCase(status.rawCode)) {
            // Alert user to clear jam
        } else if ("OUT_OF_PAPER".equalsIgnoreCase(status.rawCode)) {
            // Alert user to load paper
        } // else if ... handle other statuses
    }
});

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PrintProgressCallback

When printing multiple labels, track each one:

import com.averydennison.addevicemanager.callbacks.PrintProgressCallback;

printerAdapter.setPrintProgressCallback(new PrintProgressCallback() {
    @Override
    public void onPrintProgressUpdate(int currentLabel, int totalLabels) {
        logger.debug("Printed {} of {}", currentLabel, totalLabels);

        runOnUiThread(() -> {
            // Update progress bar
            int percent = (currentLabel * 100) / totalLabels;
            progressBar.setProgress(percent);
            progressText.setText(currentLabel + " / " + totalLabels);

            // Check if done
            if (currentLabel == totalLabels) {
                showToast("All labels printed!");
                hideProgressBar();
            }
        });
    }
});

Then print multiple copies:

// Print 50 labels — progress callback fires after each one
printerAdapter.print("ShelfTag.ngt", "PRICE=9.99", 5);

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Best Practices

1. Register Callbacks Early

Set up callbacks right after getting your adapters:

private void onDeviceConnected() {
    printerAdapter = deviceAdapter.getPrinterAdapter();
    scannerAdapter = deviceAdapter.getScannerAdapter();
    
    // Set up callbacks immediately
    deviceAdapter.setConnectionStateCallback(...);
    printerAdapter.setPrinterStatusCallback(...);
    printerAdapter.setPrintProgressCallback(...);
    scannerAdapter.setScanCallback(...);
}

2. Always Update UI on Main Thread

Callbacks may fire on background threads. Use runOnUiThread():

@Override
public void onPrinterStatusChanged(PrinterStatus status) {
    // This might be on a background thread
    runOnUiThread(() -> {
        // UI updates here
        statusText.setText(status.getDescription());
    });
}

3. Handle All States

Don't ignore edge cases:

@Override
public void onConnectionStateChanged(DeviceConnection conn, DeviceConnectionState state, String reason) {
    switch (state) {
        case CONNECTING:
            showLoadingIndicator();
            break;
        case CONNECTED:
            hideLoadingIndicator();
            enableFeatures();
            break;
        case DISCONNECTING:
            showLoadingIndicator();
            disableFeatures();
            break;
        case DISCONNECTED:
            hideLoadingIndicator();
            handleDisconnect(reason);
            break;
    }
}

4. Log Callback Events

Callbacks are great for debugging:

@Override
public void onConnectionStateChanged(DeviceConnection conn, DeviceConnectionState state, String reason) {
    logger.info("Connection state: {} -> {} ({})", conn.getName(), state, reason);
    // ... handle state
}

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Troubleshooting

Problem	Solution
Callback never fires	Ensure you registered it before the event occurs
UI doesn't update	Use runOnUiThread() for UI changes
Callback stops working	Check if adapter was recreated without re-registering callback
Missing status updates	Verify device is connected and supports the feature

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Next Steps

Guide	What You'll Learn
Getting Started	Basic setup and connection
Printing	Print labels
Scanning	Barcode scanning callbacks
Logging	Debug callback issues
Error Handling	Handle failures from callbacks