How WeChat Pay Built a C++ Cross‑Platform Architecture to Boost Mobile Development Efficiency

Background

WeChat Pay, as a critical business, faces many client‑side issues, the most fundamental being the split‑platform implementation:

Inconsistent iOS and Android implementations

Easily leads to bugs

Communication cannot guarantee quality

Poor scalability, slow response to business needs

Long iteration cycles

Incomplete data reporting

Incomplete quality‑assurance system

Lack of business and design knowledge accumulation

Loose protocol management

No unified automated testing

Inconsistent user experience (see the previous Android and iOS checkout screens)

To solve the core split‑platform problem and address technical debt, we built a C++ cross‑platform framework and refactored the core payment flow. The framework covers iOS from version 7.0.4 and Android from version 7.0.7.

Online Metrics

Example for iOS:

Crash rate remained stable before and after launch, with no impact on WeChat stability; users did not notice the switch.

Performance improvement The cross‑platform payment flow consists of 3,512 lines of code, compared with 6,328 lines for native iOS – a reduction of nearly 45%. For new feature development:

Cross‑platform implementation: 3 person‑days for iOS + Android, completed before the freeze.

Native implementation: about one week after the freeze for iOS and Android.

Thus, the cross‑platform architecture improves quality assurance and productivity.

For those interested in building a C++ cross‑platform framework from scratch, download the QCon 2019 keynote Keynote .

What Is Software Architecture?

Software architecture can be defined in many ways, from coding standards to release processes. For WeChat Pay, we define it as the system components and their communication relationships, essentially the MVC or MVVM patterns.

Why Do We Need Architecture?

Since 1986, the myth of the man‑month has highlighted that software complexity stems from complex business requirements. Architecture manages this complexity by separating responsibilities, enabling code reuse, and improving productivity.

Building a Payment Cross‑Platform Architecture from Scratch

In the mobile client domain, C++ is used for business logic, but there was no mature architecture for UI and navigation. Simply applying existing architectures would not suffice.

1. Abstract Business Processes

Common patterns like MVC, MVP, MVVM handle UI but ignore business flow and page transitions. We abstract the business flow into a UseCase and the UI into a UIPage, allowing a large process to be decomposed into smaller, reusable units.

Benefits:

Business logic aggregates in UseCase instead of being scattered across ViewControllers/Activities.

Business flow and UI become reusable.

Matches the complex, multi‑step nature of WeChat Pay.

2. Add a Routing Mechanism

Routing passes data to a central router, which parses it and triggers actions. The payment domain model becomes the routing payload.

Special flows (WebView, mini‑programs, pop‑ups) are handled uniformly by the router.

3. Manage Network Requests

Old architecture used a singleton network center, causing one‑to‑many communication issues and lifecycle problems. The new design treats each request as an independent Cgi object, created by a UseCase and bound to its lifecycle.

Advantages:

Eliminates one‑to‑many bugs.

Lifecycle tied to business logic, preventing stray callbacks.

High cohesion, low coupling, with unified caching and encryption.

4. Standardize Data Transfer

Old architecture used a shared model (blackboard pattern), leading to data pollution and untraceable flows. The new approach uses value‑type data, single‑direction injection, and the proxy pattern for notifications.

Results:

Eliminates data contamination.

Data flow becomes single‑direction and traceable.

Summary

The essence of software complexity lies in complex business requirements; architecture manages that complexity. A well‑designed architecture not only fixes legacy defects but also empowers business, delivering benefits such as automated data reporting, duplicate‑payment prevention, and security cross‑cutting. The WeChat Pay cross‑platform architecture will continue to evolve as new payment features emerge.