iPhone How To Save View States

I have been developing iphone applications for around 3months now and theres a few things that stump me and i don't really have an idea how to work round them.

I have a navigation controller controlling the v开发者_开发问答iews in my application however every screen that is loaded, used then pushed back loses all the information as it seems to be reinstantiated... I believe this is a possible memory management issue?

But how to i create an app that navigates and retains all information in its views until the application is closed.

Thanks :)

---

Possible you didn't keep a reference to the view controller, the issue is for UIVIewController not to be released.

Make the view controller an ivar you will instanciate only one time when you push it on stack.

// in .h
MyViewController *mVC;

// in .m
// maybe when the user selects a row in a tableview
if(mVC == nil) {
    // first time use, alloc/init
    mVC = [[MyViewController ....];
}
// then push on the stack
[self.navigationController ....];

Of course don't forget to release it later.

---

In this part:

MyViewController *myViewController=[MyViewController alloc] initWithNibName:@"myView" bundle:nil];
[[self navigationController] pushViewController:myViewController animated:YES];
[myViewController release];

You will probably have something like this... Instead, make your myViewController a class's property so you have a reference to it. And drop the [myViewController release]; statement.

---

Possibly your app is receiving a didReceiveMemoryWarning.

In such cases, when the super class is called, the framework does memory cleaning by unloading all the views that are not currently displayed. This could explain the behavior you are seeing.

To check it further, override didReceiveMemoryWarning in one of your view controllers or applicationDidReceiveMemoryWarning in your app delegate, and put a breakpoint in it. Don't forget to call [super...] appropriately, otherwise pretty soon your app will be killed. What you should see in this way is that the views do not disappear before hitting the breakpoint, and do disappear after that.

If the hypothesis is correct, you should find a way to save the state of your view in viewDidUnload and restore it in viewDidLoad. Look also at didReceiveMemoryWarning reference.

---

Try to save data in NSUserDefaults it its small or use plist or it its too small like 5-10 objects save in in some variable in appDelegate, and if its too large use sqlite and for saving something like images of files like xml use Document directory

---

The UINavigationController works like a stack: you push and pop UIViewControllers on it. That means when a UIViewController get popped, it will have its retain count decremented by 1, and if no other object holds a reference to it, it will be deallocated. You can avoid the UIViewControllers getting dealloced by keeping a reference to them yourself by calling -retain on the objects, for instance in your appDelegate.

---

You can use NSUserDefaults to save the states of the UIControls in the view.

So whenever u r loading a view, set the values to the controls so that it looks like it resume from the place where we left.