DataGridView Cell Validation and Row Errors

Validation in Wisej.NETModule 6The lesson guide, the walkthrough video, the knowledge check and the hands-on lab this sample was built from are on learnwisej.com — free, with an AI tutor in every lesson.

Open the course

The contacts grid rejects uncommitted bad email/age values, explains conversion failures, marks Closed rows without a date and checks every row before saving the working copy. This folder is the complete application at this point in the course, with its own solution and port.

The source of this sample

iceteagroup/LearnWisej-SamplesValidation in Wisej.NET Course/Module 6

Browse this folder on GitHub

Or clone it: git clone https://github.com/iceteagroup/LearnWisej-Samples.git — then open ValidationClinic.slnx in Visual Studio and press F5.

Run it

Requirements: .NET 10 SDK and NuGet access to Wisej-4 4.1.0. Use a Wisej development license or trial as required by your installation. No database setup or external service is needed.

cd "Validation in Wisej.NET Course/Module 6/ValidationClinic"
dotnet run -f net10.0 --urls http://localhost:5906

Open http://localhost:5906. In Visual Studio, open ValidationClinic.slnx and press F5. The project targets both net10.0-windows and net10.0, so the CLI needs -f when running.

What to try

Action	Expected result
Double-click a grid email, type missing-at-sign, then Tab	CellValidating reads FormattedValue, refuses the edit and puts a message on the cell and in the summary.
Type abc, -1 or 121 in Age	The cell rejects each value; 0 and 120 pass. Escape cancels an invalid edit.
Set Status to Closed with no closed date	The row header and date cell both show the rule, and the visible summary explains it.
Type not-a-date in Closed date	DataError suppresses the conversion exception and logs technical details on the server.
Correct the date; Save grid	Every non-placeholder row is rechecked, including annotations and shared business rules, then saved together.
Start a new row but leave required fields blank; Save grid	The partially entered contact is validated; only the untouched placeholder is skipped.
Load valid values, choose Fail next write, then Save	A friendly system message appears; the write count does not change. Save again to recover with the same input.
Discard grid edits	Restores the last saved snapshot. Working-copy edits are not persisted automatically.

The repository starts with Ada Lovelace and Grace Hopper. Every browser session owns its own repository. Its data disappears when the session ends or the app restarts. The live trace shows which validation stage ran; the write count provides visible evidence that rejected input never called a successful write.

Design notes

Module note records the API choices and failure behavior.

The sample uses AutoValidate.EnableAllowFocusChange: errors remain visible while the user reaches another field to fix a related value. Cancel never causes validation. Save explicitly validates every relevant layer. The in-memory repository is deliberately a storage stand-in; callers own validation, as in the lesson. It checks name uniqueness and swaps the saved snapshot only after all repository checks pass.