ios - Retain view state upon reloading

Question

I am developing an iPad application that is essentially a sequence of user instructions to mimic a real life system test, with the ability to make modifications on each view if components were to fail (indicating issues that will need to be resolved).

The problem I am having is that the default behaviour of the views seems to be that as I progress forward through the hierarchy, it retains the state of each view, but if I progress back and then move forward again it will have reset the screen.

What I would like to do is have each view save its state, regardless of how the user leaves that screen, so that they can be confident that their work is preserved even if they need to return to a previous step.

Is there any way of doing this? Or do I need to fundamentally reconsider my design?

Answer 1

You need model objects for your views. These could be as simple as dictionaries or as involved as a custom class for each view.

Each view's controller must update its associated model with the changes made via its interface before the view goes off-screen. When it reappears, the VC will update the display with the information from the model.

This follows the dominant Cocoa paradigm of Model-View-Controller (see also: Cocoa Design Patterns); your views display information, your models store information, and the controllers mediate and translate between the two of them.

How to update a model from the view depends heavily on the design of your model. Here's a mockup that may or may not be helpful. All the things named xField are outlets to UITextFields.

// When the view is taken off screen
- (void) viewWillDisappear {

    // Assume that when created, view controller is given a pointer 
    // to the relevant model object (probably by the previous view
    // controller)
    [model setNameOfHorse:[[self horseNameField] text]];
    NSUInteger newBetValue;
    newBetValue = [[dollarValueFormatter 
                        numberFromString:[[self betField] text]] 
                    unsignedIntegerValue];
    [model setBet:newBetValue];
    [model setNote:[[self noteField] text];
}