6. Display transaction context

Overview

After each transaction, your digital wallet application can display transaction details.

NFC Wallet SDK provides a TransactionContext in these callbacks:

• ContactlessPaymentServiceListener.onTransactionCompleted()
• ContactlessPaymentServiceListener.onError()

Treat TransactionContext as sensitive data.

Call TransactionContext.wipe() after you finish using it.

SDK integration

Read and format transaction details

Read the values you need from the context, then format them for display.

MyPaymentListener.java

@Override
public void onTransactionCompleted(TransactionContext ctx) {
    try {
        TransactionData data = TransactionData.from(ctx);
        // Display data in your UI.
    } finally {
        ctx.wipe();
    }
}

@Override
public void onError(
        TransactionContext ctx,
        PaymentServiceErrorCode errorCode,
        String message) {

    if (ctx == null) {
        // Handle the error when no transaction context is available.
        return;
    }

    try {
        TransactionData data = TransactionData.from(ctx);
        // Display data and error details in your UI.
    } finally {
        ctx.wipe();
    }
}

/**
 * Convenience data class for transaction display.
 */
public class TransactionData {

    private final String currencyCode;
    private final double amount;
    private final String transactionDate;
    private final String transactionType;
    private final String transactionId;

    private TransactionData(
            String currencyCode,
            double amount,
            String transactionDate,
            String transactionType,
            String transactionId) {
        this.currencyCode = currencyCode;
        this.amount = amount;
        this.transactionDate = transactionDate;
        this.transactionType = transactionType;
        this.transactionId = transactionId;
    }

    public static TransactionData from(TransactionContext ctx) {
        String currencyCode = TransactionDisplayUtils.bcdToString(ctx.getCurrencyCode());
        String transactionDate = TransactionDisplayUtils.bcdToString(ctx.getTrxDate());
        String transactionType = TransactionDisplayUtils.getTransactionType(ctx.getTrxType());

        return new TransactionData(
                currencyCode,
                ctx.getAmount(),
                transactionDate,
                transactionType,
                ctx.getTrxId());
    }

    public String getCurrencyCode() {
        return currencyCode;
    }

    public double getAmount() {
        return amount;
    }

    public String getTransactionDate() {
        return transactionDate;
    }

    public String getTransactionType() {
        return transactionType;
    }

    public String getTransactionId() {
        return transactionId;
    }
}

Convert BCD values for display (utility)

The following utility converts BCD-encoded values to strings.

Adjust the formatting to match your UI and your payment network requirements.

TransactionDisplayUtils.java

public final class TransactionDisplayUtils {

    private TransactionDisplayUtils() {
        // Utility class.
    }

    public static String bcdToString(byte[] bcd) {
        if (bcd == null) {
            return "";
        }

        StringBuilder sb = new StringBuilder();
        for (byte b : bcd) {
            sb.append(bcdToString(b));
        }
        return sb.toString();
    }

    public static String bcdToString(byte bcd) {
        int high = (bcd & 0xF0) >>> 4;
        int low = (bcd & 0x0F);
        return String.valueOf(high) + low;
    }

    public static String getTransactionType(byte trxType) {
        switch (trxType) {
            case 0:
                return "PAY";
            case 32:
                return "REFUND";
            default:
                return "TRANSACTION";
        }
    }
}