Migrating from WinForms or WPF to Qt: when does it make sense?

Moving from WinForms or WPF to Qt makes sense when it removes a specific barrier to your product's development, such as the lack of a version for customers using Linux or macOS. If the application will stay on Windows and the problem is slow searches, difficult workflows or the cost of making changes, first compare migration with improving the existing application. Choosing Qt does not, by itself, guarantee better performance or lower costs.

For someone responsible for the product, the key question is what the business will gain from the rebuild. A different look can be part of the change, but it does not explain its value. Start with a specific need: a user must be able to complete a task on another operating system, work with a different device or stop repeating a cumbersome step.

When staying with WinForms or WPF is worth considering

WinForms and WPF are used to build Windows applications. That platform limitation does not mean every application built with them needs replacing. WPF offers extensive interface capabilities, and Microsoft provides guidance on modernising WPF applications on .NET, including compatibility with existing libraries and code.

If staff will continue to use Windows, include an option for improving the current application. That might involve making searches faster, simplifying a form or separating lengthy processing from the interface so that it remains responsive. First establish what causes the problem. Rewriting the interface will not remove a delay in an external system whose response the application is waiting for.

Compare both options against the same expected outcome. Otherwise, a quote for a small fix and a quote for rebuilding the whole product may look like alternatives even though they cover very different work. Also account for the features that will have to wait while the migration is under way.

What Qt offers beyond Windows

Qt supports Windows, Linux and macOS in specific configurations. The list of supported platforms depends on the Qt version, operating system and modules used. This lets you share development work on parts of the application across platforms, but the complete product still needs checking on each one.

Before asking for an estimate, establish which operating systems customers actually need. “Perhaps macOS one day” is a different reason from an order that requires the product to run on particular computers. In the latter case, check printers, scanners, sign-in, reports and other parts of everyday work too. Having a Qt interface available does not establish that these dependencies will work.

Supporting several operating systems also means delivering new releases for them. Qt describes separate deployment procedures for each platform. The scope should therefore include installation, updates and a test on a user's computer without development tools installed.

Assess the interface and the business rules separately

WinForms or WPF interfaces use different components from Qt interfaces. Qt provides Qt Widgets and Qt Quick for building the interface. A migration needs a plan for reproducing the behaviour users rely on: a similar-looking button or table does not mean all its functions will work the same way.

Assess calculations, approval rules, data handling and connections to other systems separately. Consider keeping some .NET logic outside the new interface if its dependencies and the way it communicates allow this. Check how that arrangement affects installation and what happens when a connection is unavailable. Assume neither that everything must be rewritten nor that all existing code can be retained at no cost.

Ask the supplier to identify what stays, what needs changing and what has not yet been assessed. The last group might include proprietary device libraries or a complex reporting tool. Checking these may matter more to the decision than producing a new welcome screen.

A trial that resolves a significant unknown

Suppose a company has a WPF application for configuring a device, and a new customer needs a Linux version. The application sends settings, receives a result and produces a PDF report. This is a hypothetical migration scenario, not a client project.

The first trial should cover that entire workflow on the target operating system. Displaying a form in Qt does not establish whether the user can complete the task. Check the device connection, whether saved settings remain compatible, the result and report, and what happens if the connection drops. If the device library only runs on Windows, a new interface does not remove that obstacle.

The trial should inform a decision to continue the migration, change the integration approach or stop the project. The first phase is meant to resolve an important unknown and update the scope, not commit the business to a technology it has already chosen.

Keeping work running during the change

A phased migration is useful when you can define clear boundaries between the old and new parts. Establish which version writes data, whether both understand the same format and what will happen to work completed after the switch if you need to revert. Keeping the old installer is not enough to solve data compatibility problems.

Where functions are closely coupled, maintaining two versions in parallel can be costly. Compare that approach with preparing a new version and moving users over in a controlled change. Either option needs tests based on everyday tasks, a way to handle support requests and someone responsible for deciding whether to withdraw a release.

Protecting everyday work matters whichever interface library you use. In our work on modernising the TimeCamp desktop application, we are developing a controlled release process and regression tests: checks that changes do not break existing features. These cover time tracking, projects and time entries. The tasks users need to carry out should define what must pass acceptance testing.

What to include in the decision and budget

The budget should cover assessing dependencies, rebuilding the necessary parts, checking data compatibility, testing on the target operating systems, preparing releases and training the team. Add maintenance of the old application until the switch, and establish responsibility for subsequent fixes. A quote that covers only recreating the screens may leave out a substantial part of the work.

Check Qt's licensing terms as well. Commercial and open source options are available, but terms differ between modules. Do not assume either that there will be no licence cost or that every product requires a purchased licence. Assess the specific components and how the application will be distributed.

You are ready to make a migration decision when you can identify the customer need, show the trial's result for the most difficult dependency and define the conditions for moving users over. If a smaller change to WinForms or WPF can meet the same needs, it deserves equal consideration.