ASP.NET Core: global handling for showing exception message in current page - asp.net-core

Question

In my application I have a set of errors that are "expected" and thus they shouldn't redirect the user to a full error page when they occur. For example, I would like to show the error message in a red box above the current page.
I can easily catch an error on a model action and show the message on the current view, but I was wondering how to do it globally.
I tried a custom middleware with TempData and a filter with ModelState, but can't wrap my head around how to actually pass the error data back to the current page.
This works for a single model (setting the error data in TempData):
public async Task<IActionResult> OnPost() {
try {
// methodThatThrows
}
catch (ApplicationError e) {
TempData["Error"] = e.Message;
return RedirectToPage("Current_Page");
}
return RedirectToPage("Other_Page");
}
For some reason, this doesn't work (in a global middleware), as TempData is empty when the redirect completes. Also setting the middleware doesn't really work with showing the other, more critical errors in the normal error page:
public class ApplicationErrorMiddleware {
private readonly RequestDelegate _next;
private readonly ITempDataDictionaryFactory _tempFactory;
public ApplicationErrorMiddleware(RequestDelegate next, ITempDataDictionaryFactory tempFactory) {
_next = next;
_tempFactory = tempFactory;
}
public async Task InvokeAsync(HttpContext httpContext) {
try {
await _next(httpContext);
}
catch (ApplicationError ex) {
HandleError(httpContext, ex);
}
}
private void HandleError(HttpContext context, ApplicationError error) {
var tempData = _tempFactory.GetTempData(context);
tempData.Add("Error", error.Message);
context.Response.Redirect(context.Request.Path);
}
}

Answer 1

By the tip of #hiiru, I went through a wild goose chase through the configuration options to find a working solution.
My issue was a missing call from the middleware HandleError-method:
private void HandleError(HttpContext context, ApplicationError error) {
var tempData = _tempFactory.GetTempData(context);
tempData.Add("Error", error.Message);
tempData.Save(); // this call was missing
context.Response.Redirect(context.Request.Path);
}
After popping that in there, the tempdata is sent with the redirection back to the original page. Note that this is using the default cookie-based temp data, so no specific configuration is needed.
Now, this works, but it might not be the best way to do this.