Hello Everyone, I have developed this Android library to easily implement UPI Payment Integration in Android app.
UPI apps are required to be installed already before using this library because, internally this API calls UPI apps for payment processing. Before using it, make sure that your device is having atleast one UPI app installed. Otherwise it will unable to process the payments.
This API is in beta, there are lot of improvements are still needed.

1. Start	2. Select UPI App	3. Complete Payment	4. Finish

You can clone this repository and just import this project in Android Studio. Sample app is in /app directory.

In your build.gradle file of app module, add below dependency to import this library

    dependencies {
      implementation 'com.shreyaspatil:EasyUpiPayment:1.0'
    }

In Android app, make any activity where you want to implement payment integration. Here, I have created MainActivity.java

You can see below code, these are minimum and mandatory calls to enable payment processing. If any of it is missed then error will generated.

        final EasyUpiPayment easyUpiPayment = new EasyUpiPayment.Builder()
                .with(this)
                .setPayeeVpa("EXAMPLE@VPA")
                .setPayeeName("PAYEE_NAME")
                .setTransactionId("UNIQUE_TRANSACTION_ID")
                .setTransactionRefId("UNIQUE_TRANSACTION_REF_ID")
                .setDescription("DESCRIPTION_OR_SMALL_NOT")
                .setAmount("AMOUNT_IN_DECIMAL_XX.XX")
                .build();

Calls and Descriptions :

To start the payment, just call startPayment() method of EasyUpiPayment and after that transaction is started.

      easyUpiPayment.startPayment();

To register for callback events, you will have to set PaymentStatusListener with EasyUpiPayment as below.

        easyUpiPayment.setPaymentStatusListener(this);

Description :

• onTransactionCompleted() - This method is invoked when transaction is completed. It may either SUCCESS, SUBMITTED or FAILED.

NOTE - If onTransactionCompleted() is invoked it doesn't means that payment is successful. It may fail but transaction is completed is the only purpose.

• onTransactionSuccess() - Invoked when Payment is successful.
• onTransactionSubmitted() - Invoked when Payment is partially done/In waiting/Submitted/Pending.
• onTransactionFailed() - Invoked when Payment is unsuccessful/failed.
• onTransactionCancelled() - Invoked when Payment cancelled (User pressed back button or any reason).

    @Override
    public void onTransactionCompleted(TransactionDetails transactionDetails) {
        // Transaction Completed
        Log.d("TransactionDetails", transactionDetails.toString());
        statusView.setText(transactionDetails.toString());
    }

    @Override
    public void onTransactionSuccess() {
        // Payment Success
        Toast.makeText(this, "Success", Toast.LENGTH_SHORT).show();
        imageView.setImageResource(R.drawable.ic_success);
    }

    @Override
    public void onTransactionSubmitted() {
        // Payment Pending
        Toast.makeText(this, "Pending | Submitted", Toast.LENGTH_SHORT).show();
        imageView.setImageResource(R.drawable.ic_success);
    }

    @Override
    public void onTransactionFailed() {
        // Payment Failed
        Toast.makeText(this, "Failed", Toast.LENGTH_SHORT).show();
        imageView.setImageResource(R.drawable.ic_failed);
    }

    @Override
    public void onTransactionCancelled() {
        // Payment Cancelled by User
        Toast.makeText(this, "Cancelled", Toast.LENGTH_SHORT).show();
        imageView.setImageResource(R.drawable.ic_failed);
    }

To get details about transactions, we have callback method onTransactionCompleted() with parameter of TransactionDetails. TransactionDetails instance includes details about previously completed transaction.
To get details, below method of TransactionDetails are useful :

Hurrah.... We have successfully implemented UPI integration in our Android app. Thank You!

We can collaboratively make it happen. So if you have any issues, new ideas about implementations then just raise issue and we are open for Pull Requests. Improve and make it happen.