I'm creating an app that has a UITableView.
The data will be comming from an XML fetched over the net. I'm using NSXMLParser for this and it works. I used my tableView controller as the delegate for this so it implements the protocol for it:
#protocol NSXMLParserDelegate;
#interface MainView : UITableViewController <NSXMLParserDelegate>
Now this works perfectly, as I've nslogged the resulting parse.
Now, I want to populate the NStableView, so Reading I find that I need to add the datasource and delegate.
UITableViewDataSource
and
UITableViewDelegate
both of which are protocols.
How would I go about doing this on the same class? can I implement more than one protocol with the same class? should I move the delegation of the parser to another object and use this controller for this purpose?
Basically the question is what is the best way to do this?
thank you
Sure, you can implement as many protocols in a class as you want:
#interface MainView : UITableViewController <NSXMLParserDelegate, UITableViewDataSource, UITableViewDelegate>
Is that the "proper" way of doing that? I don't think there's a "right" answer to that. A purist might say no. I'd say do it where is makes sense, but err on the side of breaking it out into separate classes. For example, if your view controller is a simple menu then it would make sense for your view controller to also be your table view delegate and data source; there's no advantage in breaking it out into multiple classes.
If you have to parse XML my intuition suggests that it's starting to get a bit more complex. Maybe have a data class that implements the data source and XML parser and a controller class?
Related
I want to do some stuff from the appDelegate in Xcode. One of these things are to change a UILabel.
ViewController *viewController = [[UIStoryboard storyboardWithName:#"Main_iPhone" bundle:nil] instantiateViewControllerWithIdentifier:#"id"];
viewController.label.text = #"heeej";
I was told this would do the trick. Doesn't work. Label doesn't change. Does anyone know what the problem is?
There are several problems:
Don't do anything in the AppDelegate except for loading the window an the initial view controllers (if needed).
You are instantiating a new view controller in the first line. I assume you already have a view controller and you want to change the label in that view controller. Than you need a reference to that view controller and use this reference to send messages to it.
The label should not be a property of the view controller. You should try to follow the design pattern Model-View-Controller or the pattern Model-View-ViewModel. Ask you preferred search engine what those are if you don't know.
id as an identifier for anything in Objective-C is a bad idea because this is used as an object type.
Edit: You don't need a reference to change a property in the view controller. Use notifications to update the label. The system sends a notification with the name UIApplicationWillEnterForgroundNotification' (see [here][1]). Add the view controller as an observer to the[NSNotificationCenter defaultCenter]` for this name and react on the notification. Read the Apple documentation if you don't know what I am talking about.
I have a very simple application test in which I want to drag and drop files in a NSImageView object.
I can already get the list of files from this action, but now I want to store this data in an array to be accessed in the View using data bindings. The only code I have that works fine with data bindings, tough, has an array in AppDelegate that I access using an Array Controller. But then, my data is inside a class I created to the NSImageView called "DropView", which extends "NSImageView" class and handles the drop action.
How can I pass the array information to make the bindings possible?
Any suggestion is welcome. Thanks!
I decided to use a singleton in a bigger project. In this smaller one I did like this:
1 - Add AppDelegate reference to the subclass (m file):
#import "AppDelegate.h"
2 - Call a method declared in the AppDelegate passing all the information needed like this:
[[NSApp delegate] doSomething:someInformation];
3 - Set all the information in the method used.
4 - Make the bindings in the interface.
The simple answer is that you should not be storing model data (the array of file URLs) in a view.
Your view should pass the list of files to some other controller object, which then stores the list of files in some sort of model object. This is what MVC is about.
One way to do this is to use the delegate pattern, where your view would declare a protocol method something like this:
#protocol YourViewProtocol
- (void)imageView:(YourImageViewClass*)aView receivedDroppedURLs:(NSArray*)arrayOfURLs;
#end
Your view would also have a weak datasource property:
#interface YourImageViewClass : NSImageView
#property (weak) id <YourViewProtocol> datasource;
#end
You would then set your controller object as the datasource of the view. The controller must conform to the protocol and implement its method:
#interface YourController <YourViewProtocol>
- (void)imageView:(YourImageViewClass*)aView receivedDroppedURLs:(NSArray*)arrayOfURLs;
#end
Then, in the view method that receives the drop, you'd do something like:
- (void)receivedDroppedURLs:(NSArray*)urls
{
if([datasource conformsToProtocol:#protocol(YourViewProtocol)])
{
[datasource imageView:self receivedDroppedURLs:urls];
}
}
The other way to do this is via custom bindings. Implementing bindings in a custom view is a bit more complicated and I'd recommend that you use the delegate/datasource pattern initially, if you're not an experienced Cocoa developer.
at the risk of a public flogging, I was hoping someone could clarify my understanding of communicating between the app controller and a window controller. Here is the scenario using xcode4.
using the default AppDelegate.h and .m as the "controller" (which is also a delegate to MainMenu.xib). Have an ivar called int counter.
Created page.xib and PageController.h and .m (subclass NSWindowController). Imported it into AppDelegate.m
Used IBAction to create and view the page object. Like this:
if (!page1) {
PageController *page1 = [[Page
if (!page1) {
page1 = [[PageControoer alloc] initWithWindowNibName:#"page"];
}
[page1 showWindow:sender];
So the new window pops and we can press buttons, etc. The code for the new window is all in PageController.h and .m. and things basically work.
That is the context, here is where I'm confused.
a) question: let's say I want to access that original ivar in AppDelegate.h called counter from PageController. Either retrieving or updating the variable. What approach would I take?
b) confirm: let's say I'm back in the AppDelegate and want to get access to a selector from page1. I believe I can do this as so: [page1 runaction]; or [[page1 variable] setStringValue:#"hello"];
(this complies but I'm not sure it really works because I can't get the changes into the xib view.)
ok and the stumper. Say another view was created with another view controller call it Page2Controller.h and .m.
c) how should data flow between page and page2 -> via the AppDelegate or directly? what would the syntax look like to connect them together?
I've been following tutorials, but they don't really cover this back and forth messaging. Thanks for all the help!
a) Generally, if you want to have data that is accessed by your controllers, it should be in a model which they are given access to in some way. You can access things in the app delegate using this method:
AppDelegate* appDelegate = [[NSApplication sharedApplication] delegate];
[appDelegate <some method>];
b) I don't understand what you're asking. If the app delegate has a pointer to page1, then yes, you can call it directly.
c) Again, you should have a data model of some sort. The controllers should update the data model when the user changes the view. You can use notifications, IBActions, and direct calls to do the updating, for example. You should look up the Model, View, Controller design pattern.
I want to implement MVC architicture in my project. So I have to implement NSObject class for NSTableView.But some delegate method is not called. How to implement this class? Please help me for this issue.
The Table View Programming Guide can teach you what you need to know.
The NSTableView class reference page lists some sample code for you to try out on your own
I have to implement an Form View, or in other words: A class that is used to put a complex input form on the screen.
The Form is built up of FormComponents. There is an addFormComponent() Method to compose the form with these. And then, the form has an isValid() Method which will go through all the FormComponents and check their associated FormValidators.
For sure this thing has a lot of "intelligence", but most of this is just a call to some other class. For example the isValid() method does cool stuff, but it really only calls the isValid() methods of the FormComponents which are registered in an array. Nothing too fancy.
Well, that beeing said, must I make a fat FormViewController for this, or is an View just fine?
My understanding of these is, that a ViewController is used when there's some big logic involved. In this case, the Form View has a template which will simply iterate over the FormComponents and include them. Each FormComponent has it's own template in turn and does it's own stuff.
I've always been struggling with ViewController and View and I think I'll keep on doing that until I get a nice R.I.P. brick... but maybe someone can clear this up a little bit ;-)
The purist in me is saying that this belongs in a ViewController. I guess maybe it would depend on the framework you are using. For example, this type of setup would be very easily implemented in a Spring Controller object. It sounds like creating a controller in your case would be a lot of extra work.
Nothing is ever set in stone. You can implement in the View for now and if this turns out to be a huge burdon, move it to a Controller class. Knowing when to refactor is the difficult part.