I downloaded the sample xamarin.mac hello world project and when I try to run I get a null reference exception on the outletes when it runs. I see the outlets get properties set to them in the MainWindow.designer.cs partial classes but when it tries to reference them in MainWindowController.cs a null reference exception is thrown.
How does the sample project work when the property definitions are in the MainWindow.cs partial class and not in the controller class. Is the sample project supposed to work out of the box?
I am not familiar with the hello world example, but I come across this problem all the time in native Mac/Xcode land and I just hit it again inside Xamarin Studio. My problem happened to be this: I have a GUI full of NSTextFields. I wired each in turn to a new outlet in MainWindowController.h, however I accidentally re-wired the second NSTextField in my list to the outet I'd previously defined for the first TextField. This automatically disconnects the previous link, and even though the outlet remains defined in the .h, the connection in the .xib is broken and thus the first outlet never gets initialized with the xib's NSTextField instance.
The solution is basically right-click the GUI element in question in interface builder and be sure its referencing outlet is actually wired up to the outlet you expect in the .h.
Related
Unannounced, the 2 notices in the image below were discovered while searching for why -applicationShouldTerminate: is not being called in AppDelegate.m on quit (Cmd+Q). It worked some time ago.
Hovering over the two yellow triangles reveals:
NSObject does not have an outlet named delegate.
The action 'terminate:' is not defined on 'NSObject'.
Xcode is not showing errors or warnings and the app builds.
-applicationShouldTerminateAfterLastWindowClosed: IS called within AppDelegate.m when the red dot of the window is clicked.
My experience with Cocoa is thin (learning). I've compared the connections for File's Owner, Application and App Delegate in 2 other projects, and think a missing window outlet might be the cause. The notices above point to something else.
I would like to make sure the connections are correct as a first step. How do I repair this?
Edit: Add image of Main Window Controller connections
Edit 2: Add image of File's Owner connections
In the main NIB of an application, the two placeholders, File's Owner and Application, both end up referring to the same object. That object is the application object, the sole instance of NSApplication or a custom subclass of it. The Application placeholder is always holding the place of the application object because that's its purpose. The File's Owner placeholder is holding the place of whatever object is specified as the NIB's owner when it is loaded at run time. When Cocoa loads the main NIB at application startup, it specifies the application object as the owner. For other NIBs, File's Owner will likely be some other object.
However, Interface Builder doesn't know that a given NIB is the main one. So, it treats those two placeholders independently.
I don't know why Interface Builder has taken to setting the class of the Application placeholder to NSObject. It should really be NSApplication. That's why Interface Builder doesn't realize that the application object has a delegate outlet and an action method -terminate:.
As it happens, the class of File's Owner is properly set to NSApplication.
So, there are two ways to fix this:
Set the class of the Application placeholder to NSApplication or, in the rare case that you're using a subclass, that subclass.
Disconnect those connection from the Application placeholder and connect them to File's Owner instead. This is the way that the standard project templates do it.
For any given main NIB, you should probably standardize on using one or the other but not both. That is, one or the other should have no connections. That way you avoid conflicting or redundant connections.
I've been fiddling with Objective-C + Cocoa and writing a fairly simple Cocoa application. Then I encountered a runtime error that has no effect on my program execution:
Could not connect the action textField: to target of class BarController
I'm experimenting with pulling some of the windows out of MainMenu.xib and loading them with separate controllers and xib files.
In one window within a new xib I've created a Text Field and linked it to an IBOutlet NSTextField (textField) in a new NSWindowController subclass. It works and I am able to use textField to update the contents of the Text Field.
I am curious why I am getting the above runtime error and I'm hoping that understanding it will clear up some of the magic around the UI construction process.
Not much magic with plain IBOutlets, really - the fun starts when using Bindings or actions sent to some yet unknown target via First Responder and the responder chain :-)
Regarding your error:
Sounds like you've connected an outlet to a target that doesn't exist in your target class?
You might have established a connection to a property in File Owner (or some other proxy object) at some point where the owner's class was e.g. MyAppDelegate.
Then you've moved the window (or other object containing the outlet) to some other .xib and now the owner's class is MyWindowController that doesn't have a property of the same name you've connected your outlet to - and voila, the runtime won't be able to establish the connection for your outlet at runtime.
Just double-check your outlets in the Interface Editor, there's probably already some kind of warning message displayed next to outlets that look fishy.
Delete or reassign them and you're done.
I created a very simple new Cocoa application, with a new class and custom controller (or object in interface builder, the plain blue cube). I connected all outlets with interface builder and assigned the custom delegate to the class. The problem is, the code does not get executed (checked by setting breakpoints), the window presents itself, and there are no errors.
The code of the class is really irrelevant, I tried once before with a proper set up and it worked there, I couldn't spot the difference however.
The key here is a separate controller together with class instead of the standard App's Delegate, to integrate the project to a bigger one.
For a Mac graphics application (not iPhone), I need something like a main method in Java, the first method that gets a program going. I've been looking at things like NSViewController and NSWindow object. I've looked around but can't find an answer to this seemingly easy question anywhere. (I am very new at this by the way)
Thanks
If you create a Cocoa project from one of the Xcode "Cocoa Application" templates, you'll get a main.m file that includes the usual startup code.
Try working through one of the tutorial projects that you'll find in the documentation.
If you are using the project templates, the startup code is in the ApplicationDelegate file. The main.m, for a Cocoa application, sets up the run loop, runs NSApplication (as you can see in the Info.plist file under the 'Principle class' key.
This then loads the nib file that is specified in the Info.plist file (under the 'Main nib file base name' key). The default is MainMenu.xib. Now have a look at this nib file.
This is already set up by the template to have a 'Files's Owner' of NSApplication (the class that loaded the nib) But There is also a blue block which represents the application delegate. This is already filled out with one delegate method one outlet.
The delegate method is applicationDidFinishLaunching: This method is called by the application. This is only one of the possible delegate methods that it can handle, but it is sent after the run loop is started but before the application receives any events. It is the common place to put your initialisation code. It is in here that you should start to set up your window, which you can get to using the pre-supplied window outlet.
This is just a quick summary. A handy referenece is on Cocoa With Love and Apple's Introduction to Application Architecture document.
I've got two controls in my Interface Builder file, and each of those controls I've created a separate delegate class for in code (Control1Delegate and Control2Delegate). I created two "Objects" in interface builder, made them of that type, and connected the controls to them as delegates. The delegates work just fine. My problem is, I need to share information from one delegate to the other delegate, and I'm not sure how.
What is the best way to do this? Combine the two delegates into one class, or somehow access a third class that they can both read? Since I'm not actually initializing the class anywhere in my code, I'm not sure how to get a reference to the actual instance of it (if there is an actual instance of it), or even access the "main" class that the project came with.
You can add outlets from either delegate to the other delegate. There are two ways to add an outlet to an object in IB (assuming you're using Xcode/IB version 3.0 or later:
If you have not generated the code for your delegate classes yet, select the desired delegate, then open the "Object Identity" tab in the IB inspector. Add a "Class outlet" of type NSObject. You should then be able to set this new outlet to the other delegate. Of course you will have to generate the code for your delegate class and add the generated source files to your Xcode project before you can load the nib.
If you've already generated the code for the delegate class (or added an NSObject to your NIB and set its Class to an existing class in your Xcode project), add an instance variable to the delegate class:
IBOutlet id outletToOtherDelegate;
As long as your Xcode project is open (as indicated by the green bubble in the lower-left of your NIB window), IB will automatically detect the new outlet and allow you to assign it to the other delegate object in your NIB.
Cocoa automatically connects these outlets at NIB load time. Once awakeFromNib is called on instances of your delegate objects, you may assume that all the other objects in the NIB have been instantiated and all outlets have been connected. You should not assume an order on calls to awakeFromNib, however.
I think you can create outlets on each one and cross-bind them so that they each have the same data all the time. If there's one model object they need to share, that's pretty tidy. I don't actually know how to do this; I think I saw it in an iPhone tutorial one time!
I don't have my Mac in front of me currently since I'm at work, but would it be possible to bind an instance of one delegate to a member of the other delegate? This would be similar to binding an NSArrayController to a member of another controller class, for example.
However, depending on what the delegate classes are doing, if the tasks are similar I would probably just combine them into once class. That would eliminate the problem altogether.