Django FormView Message Persistence Issue

The issue you're experiencing is related to how extra_context works in Django class-based views. The extra_context attribute is a class attribute, not an instance attribute. This means it's shared across all instances of your view class.

When you modify self.extra_context directly in your get() method, you're actually modifying the class attribute that's shared across all requests to this view. This is why the message persists even when the query parameter is no longer present.

Solution

Instead of modifying self.extra_context directly, you should override the get_context_data() method to add your conditional context data:

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class MyView(LoginRequiredMixin, FormView):
    # Your other view attributes...
    
    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        param = self.request.GET.get("param")
        if param == "showme":
            context["showme"] = {"some text on a message box"}
        return context

This approach ensures that the context is generated fresh for each request, and the message will only appear when the query parameter is present.

Alternatively, if you want to keep your current structure, you can initialize a new dictionary for each request:

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class MyView(LoginRequiredMixin, FormView):
    def get(self, request, *args, **kwargs):
        """Handle GET requests: instantiate a blank version of the form."""
        
        # Create a new dictionary for each request
        self.extra_context = getattr(self, 'extra_context', {}).copy()
        
        param = request.GET.get("param")
        if param == "showme":
            self.extra_context["showme"] = {"some text on a message box"}
        return super().get(request, *args, **kwargs)

The get_context_data() approach is generally preferred as it's the Django-recommended way to customize context data in class-based views.