I have an app where on the main view that is initially loaded, it will have an indicator that will show how many items are in a tableview that is in another class. I presume I have to preload the tableview class while the app is launching so the indicator can update correctly, how can I do this?
What is the table's datasource? I'd say if the data in the table is coming from a plist or other file, you could load the file into an array in the main view's class, be able to get a count from that, and then just reference it from this class when you need it in the tableview class. But if the datasource is coming from information generated mainly inside the tableview class, then I'd think you'd have to load it all first.
A table view's job is just to be the view that represents some data model. That data model is usually an array of some kind that represents items in database, a plist, somewhere online, etc.
You shouldn't be thinking about invisibly preloading the actual table view here-- that's overkill and breaks the MVC design-- the count of the items is a function of that underlying data model, so just preload the data model (or do whatever you need to do to load the item count).
There are multiple ways to pass around or share a reference to that underlying data model once its loaded, so you can use it from both views, but you'll have to say more about the structure of your app (and probably ask another question) to get good advice on that.
Related
I have the following (view) controller arrangement:
an uitableview --(embedded in)--> navigation controller --(embedded in)--> Tab bar controller --(modal segue to)--> button in a view (uiviewcontroller).
description of my problem:
The view with the button is the initial view of my app. Pressing this button leads to a tableview in a tab bar. At the beginning the table view is empty, but you can manually add information on the cells, like names. However, once you go back to initial view (with button) and press the button again, the previous entries in the table view are erased.Can somebody give a hint how to retain these entries with the given arrangement. Thank you very much in advance.
You can use the singleton pattern. It will create a shared instance of your object, that you can access anywhere. You will then be able to write in it when the user adds a row in the table, and read it when you come to the tableView.
Here is a bit of help : Singleton pattern
EDIT : you can also use core data, but it may not be appropriate in your situation (plenty of docs on the web about that one)
This is quite a question as it really isn't about the interface per se. It is more to do with general Object Orientated Programming and the life time of objects.
Basically your data needs to be stored higher up the object hierarchy. It needs to persist across construction/destruction of the interface objects. This could also be done by storing the data in persist-able data store such as a DB or file but you would still need to store the means to extract the data or subset of data from the store.
If you wish to persist the data you could store data in a singleton data class and reference it statically or store it in your UIApplication object and pass that down the hierarchy as you create each object. you would probably have to subclass each object and add a new constructor passing in a ref to the data.
Any advice on where to store the main list data for an iPhone application like the following?
NavigationController based
Level 1 (main screen) is a List of Items. Hence it uses a table view (table of items)
Level 2_EDIT: Is a view you can get to from the main screen by clicking EDIT. Here you can add text to be added to the main view list
Level 2_DETAIL: Is a view you can get to from the main screen by clicking on a cell.
Now assuming the implementation is (rough overview):
* MainView - appDelegate (holds UIWindow & UINavigationController)
* RootViewController - table view of the main items list (? variables here ?)
* EditViewController - input text to add to main list
* DetailViewController - shows detail of record
Question - Where to hold the NSArray that keeps the main list of items? Should it be in the RootViewController where the Table View exists that displays it? Or should it be higher up in the ApplicationDelegate? I note that when you go from RootViewController to EditViewController, then in this edit view you would have to ADD items to the array, so would it be easier for the code in the EditViewController to access the main array from the AppDelegate (as opposed to the RootViewController)?
(Note - still haven't made an app that has a specific model object, re MVC, yet, so not sure if this should come into the picture.)
Your data becomes the table view's data source, and although it doesn't have to, the view controller that contains the table view often does the data source's role. The view controller can also be a delegate for the EditViewController, so the EditViewController sends a message to it so it can update the array.
Apple's CoreDataBooks sample project show similar architecture. You may want to take a look.
Having the array in the application delegate is often not a great idea. Although it can give you a little bit of convenience, now your classes totally depend on your application delegate unnecessarily.
Your table view shows your data. This corresponds to View in the MVC design pattern. I assume RootViewController is the view controller of the table view, which acts as a Controller in the pattern. Your data, the location of which is not decided yet, corresponds to Model. The role of RootViewController becomes connecting the Model and View.
The ideal, or the reason of the MVC pattern is to isolate the model and the view, so the model can work with other views with appropriate controllers, and the view can also work with other models with appropriate controllers. For example, your RootViewController will provide the table view with data. It will specify the data in the language of table view, e.g. the number of sections and rows, the contents of cells, etc. If you want to present the data in a different way, for example a graph, your controller will access the same data (model) and provide the graph view with a different representation of the same data. The model need not change, neither do the views. You write only the controller, for each combination of a model and a view.
Ideally, therefore, you will have a different class for the model. In this class, you will store the array, and provide a general interface for controllers can interact with the data.
However, it's often not that necessary, either because it's unlikely that you will use the model class often again, or because the model itself is way too simple so it can be easily implemented anywhere. For example, if your data for the table is a simple array, an NSArray object is often sufficient for the model's role. Therefor, here comes an idea that to combine the controller and the model into a single object.
This is why it makes sense that your table view controller often acts as the data source of the table view.
However, storing the data in the application delegate is a completely different idea. Now the application delegate becomes your model, but which does not make sense, because the application delegate is only used for the specific application. Why would you have a separate model object that totally depends on a single application? Also, if your table view directly interacts with the application delegate, it means that now your view cannot work for other applications either because it now depends on the specific application's application delegate.
Often the reason why people are tempted to have data in the application delegate is, that the application delegate is easily accessible by any objects in the application by using [UIApplication sharedApplication].delegate. The M-V-C relationship is not always very simple. For example, your EditViewController also need to access the same model. To do this, you have to write some code to make the model accessible by both the table view and the edit view. If you have the data in the application delegate, you don't need to do anything, because you can magically access the array by accessing the application delegate.
But that's all. A few minute's saving in your coding time, for the price of ruining your software architecture. I'm not a fundamentalist, and I do sometimes use application delegate to store some data when I'm absolutely sure that it's not worth to provide well-formed interfaces, but it's rare.
So how should you connect your edit view to the data merged into the table view controller? There could be multiple ways. What I suggested before is let the edit view controller has a weak reference to the table view controller (delegate) and send a defined message, for example - (void)editViewController:(EditViewController *editViewController) didFinishEditing:(id) someData. In this way, you can use this edit view controller with some other view controllers as long as they use the same protocol. But others may implement different interfaces for it.
You need to store in the appDelegate,as you can acees the data in anyviewcontroller then.But if you use rootviewController,then you can only send data to next ViewController then,not to the 2nd or 3rd ViewController directly.
Hope it will help you.
Good Luck
I have a program that displays a list (a TableView).
When the user clicks an item, it's detail is shown.
On the detail view, the user can ask to modify it so a modify window is shown.
Here, the user can ask to delete the item.
I would like at this time return to the list with the item deleted from the list and from the data source.
There may be thousands of methods to do this, but I wonder which is the best / good one.
Could you help me, and/or give me a good reference to read about this ?
I think he ask how to get from view number 3 back to first view.
Then you can put your three views inside a UINavigationController and call on the last view popToRootViewControllerAnimated:
at least Two options:
Delegation - Create a protocol called something like: TableDetailModifierDelegat
and add methods like modifierDidChangedItem:(id)item
or modifierDidDeleteItem:(id)item
and to the modifying view controller add instance variable id so when you done editing or deleting you will call the appropriate methods.
of course you will need to make your table view controller implement the protocol you created. if you modified or deleted an item you should update your data source and reload the data to the table.
also pass the Table View Controller as the delegate when creating the Modifying View Controller.
Passing The Data Model.
This is much more simple to implement.
you can simply pass your data model to the modifying view controller, and make the changes directly to the data model.
You should keep the data model as Instance Variable in the modifying view controller.
when you done, dont forget to reload the data to your table.
In this instance, you could simply remove the data from the data source the UITableView is using and then call the reloadData method on the table. (As you're editing the data in question, you'll presumably have a suitable method/reference by which to delete it.)
As a bit of reading, I'd recommend Apple's Table View Programming Guide for iOS - this provides a lot of useful background information.
I'm currently working on an app that uses a UINavigationController inside UITabBars. The tab bars correspond to both UITableViews as well as a Map View. However, the root view controller of the app is not the parent, or direct parent, of the UITableView custom controllers and map view controller. I also have a p-list that creates NSDictionary objects; it is the datasource that I am using to populate entries in the tables and the map.
So, without a root view controller, how should I create the NSDictionary objects from the data source? It seems to me that the easiest way is to simply recreate the object in each view controller for a view that needs the data. Because I don't have that many views and the p-list isn't that long, memory shouldn't be an issue. However, I do know that this is all very inefficient.
Is there any alternative implementation so that I don't have to recreate the NSDictionary in each view controller?
This tutorial featuring the singleton guide neatly explains everything:
http://www.cocoanetics.com/2009/05/the-death-of-global-variables/
My only worry now is if multiple view controllers each call the singleton, wouldn't they all be generating multiple instances of the NSDictionary, and couldn't that conceivably still take up a lot of memory?
You need a data model object that stores the data for application.
A data model is a customized, standalone object accessible from anywhere in the application. The data model object knows nothing about any views or view controllers. It just stores data and the logical relationships between that data.
When different parts of the app need to write or read data, they right and read to the data model. In your case, view1 would save its data to the data model when it unloads and then view2 would read that data from the data model when it loads (or vice versa.)
In a properly designed app, no two view controllers should have access to the internal data of another controller. (The only reason a view controllers needs to know of the existence of another controller is if it has to trigger the loading of that other controller.)
The quick and dirty way to create a data model is to add attributes to the app delegate and then call the app delegate from the view controllers using:
MyAppDelegateClass *appDelegate=[[UIApplication sharedApplicaton] delegate];
myLocalProperty=appDelegate.someDataModelProperty;
This will work for small project but as your data grows complex, you should create a dedicated class for your data model.
Placing the data in an init method or a viewDidLoad won't work because in a tabbar the users can switch back and forth without unloading the view or reinitializing the view controller.
The best place to retrieve changing data is in the viewWillAppear controller method. That way the data will be updated every time the user switches to that tab.
In practical terms, a data model is usually either placed in some kind of a singleton (either your own, or the app delegate which is a kind of singleton).
You should read up on Model-View-Controller (MVC) architecture. Specifically, you'll probably want to introduce a data model where you would create and populate the dictionary during initialization and then access it from all of your view controllers.
My application has a series of table views based on some hierarchical data. For example, the user selects "Browse by XYZ" on my CategoryListController, and then I load my DocumentListController based on that selection.
Right now I'm getting the list through a web service that returns some JSON data, but that's beside the point. I could retrieve this dynamic list from a SQLite database, and I would have the same underlying challenge.
The problem here is that since the list of items for my table view in DocumentListController will change depending on which selection the user tapped on, I have to load my list after the table view is displayed.
Right now I'm using -viewWillAppear: to trigger this "refresh" of the data items from my web service. I was wondering if this is the best way to be doing this refresh, or if I should look into using a different method. I tried using -viewDidLoad but that method gets called only once for the DocumentListController, and I have to check at every invocation if the "selection" has changed, and if so, I need to call my web service again.
What's the best way to do something like this?
Since you retrieve the data through the network, I would suggest to post a notification after you process it. Your DocumentListController should register for that notification and invoke its table view's reloadData in the notification handler.
Another approach, if the data will always be there when displaying the view, is what you've suggested - update table view in viewWillAppear.