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• Polymorphic NHibernate mappings

  - by Ben Aston

  I have an interface IUserLocation and a concrete type UserLocation. When I use ICriteria, specifying the interface IUserLocation, I want NHibernate to instantiate a collection of the concrete UserLocation type. I have created an HBM mapping file using the table per concrete type strategy (shown below). However, when I query NHibernate using ICriteria I get: NHibernate cannot instantiate abstract class or interface MyNamespace.IUserLocation Can anyone see why this is? (source code for the relevant bit of NHibernate here (I think)) My ICriteria: var filter = DetachedCriteria.For<IUserLocation>() .Add(Restrictions.Eq("UserId", userId)); return filter.GetExecutableCriteria(UoW.Session) .List<IUserLocation>(); My mapping file: <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-lazy="true"> <class xmlns="urn:nhibernate-mapping-2.2" name="MyNamespace.IUserLocation,MyAssembly" abstract="true" table="IUserLocations"> <composite-id> <key-property name="UserId" column="UserId" type="System.Guid"></key-property> <key-many-to-one name="Location" column="LocationId" class="MyNamespace.ILocation,MyAssembly"></key-many-to-one> </composite-id> <union-subclass table="UserLocations" name="MyNamespace2.UserLocation,MyAssembly2"> <property name="IsAdmin" /> </union-subclass> </class> </hibernate-mapping>

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• iPhone - return from an NSOperation

  - by lostInTransit

  Hi I am using a subclass of NSOperation to do some background processes. I want the operation to be cancelled when the user clicks a button. Here's what my NSOperation subclass looks like - (id)init{ self = [super init]; if(self){ //initialization code goes here _isFinished = NO; _isExecuting = NO; } return self; } - (void)start { if (![NSThread isMainThread]) { [self performSelectorOnMainThread:@selector(start) withObject:nil waitUntilDone:NO]; return; } [self willChangeValueForKey:@"isExecuting"]; _isExecuting = YES; [self didChangeValueForKey:@"isExecuting"]; //operation goes here } - (void)finish{ //releasing objects here [self willChangeValueForKey:@"isExecuting"]; [self willChangeValueForKey:@"isFinished"]; _isExecuting = NO; _isFinished = YES; [self didChangeValueForKey:@"isExecuting"]; [self didChangeValueForKey:@"isFinished"]; } - (void)cancel{ [self willChangeValueForKey:@"isCancelled"]; [self didChangeValueForKey:@"isCancelled"]; [self finish]; } And this is how I am adding objects of this class to a queue and listening for KVO notifications operationQueue = [[NSOperationQueue alloc] init]; [operationQueue setMaxConcurrentOperationCount:5]; [operationQueue addObserver:self forKeyPath:@"operations" options:0 context:&OperationsChangedContext]; - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { if (context == &OperationsChangedContext) { NSLog(@"Queue size: %u", [[operationQueue operations] count]); } else { [super observeValueForKeyPath:keyPath ofObject:object change:change context:context]; } } To cancel an operation (on a button click for instance), I tried calling -cancel but it doesn't make a difference. Also tried calling -finish but even that doesn't change anything. Every time I add an operation to the queue, the queue size only increases. finish is called (checked using NSLog statements) but it doesn't really end the operation. I'm still not very confident I'm doing this right Can someone please tell me where I am going wrong? Thanks a lot

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• Java complex validation in Dropwizard?

  - by miku

  I'd like to accept JSON on an REST endpoint and convert it to the correct type for immediate validation. The endpoint looks like this: @POST public Response createCar(@Valid Car car) { // persist to DB // ... } But there are many subclasses of Car, e.g. Van, SelfDrivingCar, RaceCar, etc. How could I accept the different JSON representations on the endpoint, while keeping the validation code in the Resource as concise as something like @Valid Car car? Again: I send in JSON like (here, it's the representation of a subclass of Car, namely SelfDrivingCar): { "id" : "t1", // every Car has an Id "kind" : "selfdriving", // every Car has a type-hint "max_speed" : "200 mph", // some attribute "ai_provider" : "fastcarsai ltd." // this is SelfDrivingCar-specific } and I'd like the validation machinery look into the kind attribute, create an instance of the appropriate subclass, here e.g. SelfDrivingCar and perform validation. I know I could create different endpoints for all kind of cars, but thats does not seem DRY. And I know that I could use a real Validator instead of the annotation and do it by hand, so I'm just asking if there's some elegant shortcut for this problem.

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• iPhone SDK - UITabBarConroller and custom design

  - by Cheryl

  Hi I am having a problem with my tab bars at the bottom of the screen. The designer has decided it should be one colour (not black) when inactive and another colour when active. I have worked out how to replace the main colour of the tabbar by subclassing UITabBarController and doing this:- - (void)viewDidLoad { [super viewDidLoad]; CGRect frame = CGRectMake(0.0, 0, self.view.bounds.size.width, self.view.bounds.size.height); UIView *v = [[UIView alloc] initWithFrame:frame]; //get percentage values from digitalcolour meter and enter as decimals v.backgroundColor = [UIColor colorWithRed:.0 green:.706 blue:.863 alpha:1]; [tabBar1 insertSubview:v atIndex:0]; [v release]; } I just can't see how to make the active tabbar be a separate colour when it is selected. I have tried subclassing UITabBarItem but there doesn't seem to be any property for me to set to change the background colour of the tab. They also want to have the icons on the tab bar not be blue and grey and I can't figure out how to do that. In the ViewController for one tab bar item I have put this into viewdidload:- myTabBarItem *tabItem = [[myTabBarItem alloc] initWithTitle:@"listOOO" image:[UIImage imageNamed:@"starcopy.png"] tag:1]; tabItem.customHighlightedImage=[UIImage imageNamed:@"starcopy.png"]; self.tabBarItem=tabItem; [tabItem release]; tabItem=nil; and in my subclass of UITabBarItem I have put this:- -(UIImage *) selectedImage{ return self.customHighlightedImage; } Only I don't see the icon at all. If I put this into the viewDidLoad of my subclass of UITabBarController:- for (UITabBarItem *item in tabBar1.items){ item.image = [UIImage imageNamed:@"starcopy.png"]; } Then all my tab bars have the icon but they are blue (and grey when inactive) how would I get them not to become blue but stay their original colour? If you have any light on this problem please help as I have been banking my head on the wall for 2 days now and it's getting me down. Thanks in advance Cheryl

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• Unable to access a primitive array inside a custom class from a UIViewController instance

  - by Daniel

  Hello! I have made a subclass of NSObject that is meant to be the model of my application. The class has a few methods and on instance primitive array as such: @interface Cube : NSObject { int cubeState[5][2][2]; } - (id)printContent; @end @implementation Cube - (void)init { if (self = [super init]) { for (int i=0; i<=5; i++) { for (int j=0; j<=2; j++) { for (int k=0; k<=2; k++) { cubeState[i][j][k] = i; } } } } return self; } - (void)printContent { for (int i=0; i<=5; i++) { for (int j=0; j<=2; j++) { for (int k=0; k<=2; k++) { NSLog(@"[%d] [%d] [%d] = %d", i, j, k, cubeState[i][j][k]); } } } } @end This works fine if instanciated from the delegate as such: #include "Cube.h" @implementation CubeAppDelegate @synthesize window; - (void)applicationDidFinishLaunching:(UIApplication *)application { Cube *cube = [[Cube alloc] init]; [cube printContent]; [cube release]; [window makeKeyAndVisible]; } However, the application crashes if I try to create a subclass of UIViewController with a Cube *cube property and later try to access the Cube instance object through the view controller's property as such: @interface CustomController : UIViewController { Cube *cube; } @property (nonatomic, retain) Cube *cube; @end @implementation CustomController @synthesize cube; - (void)dealloc { [cube release]; [super dealloc]; } @end and in the delegate: - (void)applicationDidFinishLaunching:(UIApplication *)application { viewController = [[CustomController alloc] initWithNibName:@"MainView" bundle:nil]; viewController.cube = [[[Cube alloc] init] autorelease]; [viewController.cube printContent]; // Application crashes here } Any ideas?

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• Jackson object mapping - map incoming JSON field to protected property in base class

  - by Pete

  We use Jersey/Jackson for our REST application. Incoming JSON strings get mapped to the @Entity objects in the backend by Jackson to be persisted. The problem arises from the base class that we use for all entities. It has a protected id property, which we want to exchange via REST as well so that when we send an object that has dependencies, hibernate will automatically fetch these dependencies by their ids. Howevery, Jackson does not access the setter, even if we override it in the subclass to be public. We also tried using @JsonSetter but to no avail. Probably Jackson just looks at the base class and sees ID is not accessible so it skips setting it... @MappedSuperclass public abstract class AbstractPersistable<PK extends Serializable> implements Persistable<PK> { @Id @GeneratedValue(strategy = GenerationType.AUTO) private PK id; public PK getId() { return id; } protected void setId(final PK id) { this.id = id; } Subclasses: public class A extends AbstractPersistable<Long> { private String name; } public class B extends AbstractPersistable<Long> { private A a; private int value; // getter, setter // make base class setter accessible @Override @JsonSetter("id") public void setId(Long id) { super.setId(id); } } Now if there are some As in our database and we want to create a new B via the REST resource: @POST @Consumes(MediaType.APPLICATION_JSON) @Produces(MediaType.APPLICATION_JSON) @Transactional public Response create(B b) { if (b.getA().getId() == null) cry(); } with a JSON String like this {"a":{"id":"1","name":"foo"},"value":"123"}. The incoming B will have the A reference but without an ID. Is there any way to tell Jackson to either ignore the base class setter or tell it to use the subclass setter instead? I've just found out about @JsonTypeInfo but I'm not sure this is what I need or how to use it. Thanks for any help!

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• Annotate over Multi-table Inheritance in Django

  - by user341584

  I have a base LoggedEvent model and a number of subclass models like follows: class LoggedEvent(models.Model): user = models.ForeignKey(User, blank=True, null=True) timestamp = models.DateTimeField(auto_now_add=True) class AuthEvent(LoggedEvent): good = models.BooleanField() username = models.CharField(max_length=12) class LDAPSearchEvent(LoggedEvent): type = models.CharField(max_length=12) query = models.CharField(max_length=24) class PRISearchEvent(LoggedEvent): type = models.CharField(max_length=12) query = models.CharField(max_length=24) Users generate these events as they do the related actions. I am attempting to generate a usage-report of how many of each event-type each user has caused in the last month. I am struggling with Django's ORM and while I am close I am running into a problem. Here is the query code: ef usage(request): # Calculate date range today = datetime.date.today() month_start = datetime.date(year=today.year, month=today.month - 1, day=1) month_end = datetime.date(year=today.year, month=today.month, day=1) - datetime.timedelta(days=1) # Search for how many LDAP events were generated per user, last month baseusage = User.objects.filter(loggedevent__timestamp__gte=month_start, loggedevent__timestamp__lte=month_end) ldapusage = baseusage.exclude(loggedevent__ldapsearchevent__id__lt=1).annotate(count=Count('loggedevent__pk')) authusage = baseusage.exclude(loggedevent__authevent__id__lt=1).annotate(count=Count('loggedevent__pk')) return render_to_response('usage.html', { 'ldapusage' : ldapusage, 'authusage' : authusage, }, context_instance=RequestContext(request)) Both ldapusage and authusage are both a list of users, each user annotated with a .count attribute which is supposed to represent how many particular events that user generated. However in both lists, the .count attributes are the same value. Infact the annotated 'count' is equal to how many events that user generated, regardless of type. So it would seem that my specific authusage = baseusage.exclude(loggedevent__authevent__id__lt=1) isn't excluding by subclass. I have tried id_lt=1, id_isnull=True, and others. Halp.

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• ActiveX control loading but not activating correctly (only when using in Reg Free COM)

  - by embnut

  I have an ActiveX control (created using C#) that I am adding to a form in Visual FoxPro using late binding. It works without problems when I register the control. I want to use reg free COM and created necessary manifest files. Now it load and displays in an inactive state until I double click or programatically activate it. I don't think it has anything to do with the reg free com manifest files. However is there something I need to do to set it up before/after making the late binding call AddObject()? this.AddObject('OleControl1', 'oleControl', 'SomeCompany.SomeOleControl') When I check the OleTypeAllowed Property of the OleControl created by AddObject() it is 1 (Embedded OLE object) instead of -2 (ActiveX object). So the OleControl got instantiated to the wrong type. I also tried the following: DEFINE(d) a subclass of OleControl and set the property OleTypeAllowed = -2. Used late binding to load the control. It did not work as required. The OleTypeAllowed came back as 1 Registered the ActiveX control. Added the ActiveX control to the project as a subclass using the visual editor. Unregistered the control. Used late binding to load the control. It did not work as required. The OleTypeAllowed came back as 1. Is it possible to load the OleControl as a ActiveX control? Any input from VB that I can convert to FoxPro would also be appreciated.

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• NSBorderlessWindow not responding to CMD-W/CMD-M

  - by Sean

  I have an NSBorderlessWindow subclass of NSWindow with a transparent and non-opaque background (so it's non-rectangular in appearance). I've added my own buttons to function as the close and minimize buttons when I click them, but for some reason the window will not respond to CMD-W or CMD-M like a normal one does. I have my NSWindow subclass set to return YES to canBecomeKeyWindow and canBecomeMainWindow. My NIB still has all the standard menu items in it that are there when you create a new project - including the "Minimize" item in the Window menu with the default shortcut CMD-M defined. It's hooked up to send performMiniaturize: to the first responder. However it is not enabled when the app is run, so it seems like it must be asking the window if it can minimize and the window says no or something. (I'm still very new to OSX/Cocoa.) What am I missing? Also, and maybe this is related, my borderless window has a shadow enabled - but unlike a normal titled window, when I make my window the active/front window by clicking on it, the shadow doesn't change. Normally an OSX focused window has a slightly larger/darker shadow to make it stand out more but mine never changes the shadow. It's like I'm missing something to make the OS treat this window as a real/normal/main window or something and as a result I lose the shadow change and functioning CMD-W/CMD-M.

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• C# reflexion, cloning

  - by Enriquev

  Say I have this class Myclass that contains this method: public class MyClass { public int MyProperty { get; set; } public int MySecondProperty { get; set; } public MyOtherClass subClass { get; set; } public object clone<T>(object original, T emptyObj) { FieldInfo[] fis = this.GetType().GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic); object tempMyClass = Activator.CreateInstance(typeof(T)); foreach (FieldInfo fi in fis) { if (fi.FieldType.Namespace != original.GetType().Namespace) fi.SetValue(tempMyClass, fi.GetValue(original)); else fi.SetValue(tempMyClass, this.clone(fi.GetValue(original), fi.GetValue(original))); } return tempMyClass; } } Then this class: public class MyOtherClass { public int MyProperty777 { get; set; } } when I do this: MyClass a = new MyClass { MyProperty = 1, MySecondProperty = 2, subClass = new MyOtherClass() { MyProperty777 = -1 } }; MyClass b = a.clone(a, a) as MyClass; how come on the second call to clone, T is of type object and not of type MyOtherClass

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• Will the following NHibernate interface mapping work?

  - by Ben Aston

  I'd like to program against interfaces when working with NHibernate due to type dependency issues within the solution I am working with. SO questions such as this indicate it is possible. I have an ILocation interface and a concrete Location type. Will the following work? HBM mapping: <class name="ILocation" abstract="true" table="ILocation"> <id name="Id" type="System.Guid" unsaved-value="00000000-0000-0000-0000-000000000000"> <column name="LocationId" /> <generator class="guid" /> </id> <union-subclass table="Location" name="Location"> <property name="Name" type="System.String"/> </union-subclass> </class> Detached criteria usage using the interface: var criteria = DetachedCriteria.For<ILocation>().Add(Restrictions.Eq("Name", "blah")); var locations = criteria.GetExecutableCriteria(UoW.Session).List<ILocation>(); Are there any issues with not using the hilo ID generator and/or with this approach in general?

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• How to add View Controller with Tab Bar interfaced View Controller

  - by TechFusion

  I have created Window based Tab Bar controller app, One Tab Bar of viewController has been interfaced with WebVIew ..I am looking to create another view once touch event happened in that WebView.. //TabBarViewController.m - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { TabMainView *mainView = [[TabMainView alloc] init]; mainView.hidesBottomBarWhenPushed = YES; [self.navigationController pushViewController: mainView animated:YES]; [mainView release]; } I have created MainView, which is UIViewController Subclass. //TabMainView.m - (void)loadView { CGRect frame = CGRectMake(0.0, 0.0, 480, 320); WebView = [[[UIWebView alloc] initWithFrame:frame] autorelease]; WebView.backgroundColor = [UIColor whiteColor]; WebView.scalesPageToFit = YES; WebView.autoresizingMask = (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleTopMargin); WebView.autoresizesSubviews = YES; WebView.exclusiveTouch = YES; //self.WebView.UserInteractionEnabled = NO; WebView.clearsContextBeforeDrawing = YES; self.view = WebView; [WebView release]; } - (void)viewWillAppear:(BOOL)animated { [self.WebView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.apple.com"]]]; } Here when touch event happened then it is not passing control to TabMainView.m 's Viewload function although I am pushing it's view? TabBarView is also UIViewController subclass not a UINavigationController.

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• C# reflection, cloning

  - by Enriquev

  Say I have this class Myclass that contains this method: public class MyClass { public int MyProperty { get; set; } public int MySecondProperty { get; set; } public MyOtherClass subClass { get; set; } public object clone<T>(object original, T emptyObj) { FieldInfo[] fis = this.GetType().GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic); object tempMyClass = Activator.CreateInstance(typeof(T)); foreach (FieldInfo fi in fis) { if (fi.FieldType.Namespace != original.GetType().Namespace) fi.SetValue(tempMyClass, fi.GetValue(original)); else fi.SetValue(tempMyClass, this.clone(fi.GetValue(original), fi.GetValue(original))); } return tempMyClass; } } Then this class: public class MyOtherClass { public int MyProperty777 { get; set; } } when I do this: MyClass a = new MyClass { MyProperty = 1, MySecondProperty = 2, subClass = new MyOtherClass() { MyProperty777 = -1 } }; MyClass b = a.clone(a, a) as MyClass; how come on the second call to clone, T is of type object and not of type MyOtherClass

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• Accessing the stringValue from NSTextFields on different NIBs

  - by Kyle Zaragoza

  I'm having an extremely difficult time trying to access information from an object (e.g. an NSTextField) that is located on a NIB other than my "MainMenu.nib". My current setup: I have a MainMenu.xib that contains only a toolbar at the top and an NSView. I have four other .xib files containing custom NSViews and each of their File Owner's are assigned to a NSViewController subclass which I have created for each. My MainMenu.xib contains an object that is set to my WindowController subclass that takes care of swapping the fours views into the NSView on my MainMenu.xib. All of this works fantastic. Where I have a problem: I have another class that acts as the brains to my application which sends and receives data from an online server, all of the methods I have created rely on inputs from the user that are located on the individual .xibs that swap into my MainMenu.xib's NSview. Unfortunately I have no idea on how to grab the information from the NSTextFields, textViews, etc. that are located on my individual .xib files. What I've tried: I have tried setting the File Owner's of the four individual .xibs to my "brains" class and connecting outlets defined in my "brains".h, but when I call [textField stringValue] I receive a NULL response. I'm thinking this is because I'm creating multiple instances of my "brains" class but not totally sure. Any help on accessing information from textFields from other nibs would be a great benefit, thanks in advance.

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• addChild, etc. using NSTreeController and NSTreeNode (snow leopard)

  - by John Velman

  I have a setup with an object (OTNodeDatum) (OT for OutlineTest) to be the represented object in NSTreeNode. NSTreeNode is the Class shown in the attributes page for NSTreeController. I have document based app, no core data. On MyDocument init, I set up content with an NSMutableArray containing one item, an NSTreeNode with a represented object which contains a single property (yes, name). Add button, Add Child button, Delete button, hooked up via interface builder to the NSTreeController add action, etc. It works up to a point. When I do an add, I get a new blank line which I can edit, but the inserted text goes away when I leave the cell. When I do a delete, things get deleted. When I do add child, nothing happens. I think I have to subclass either NSTreeNode, or NSTreeController to get the right behavior in terms of adding children and adding a new represented object in addition to adding a new tree node. IS this on the right track? If I subclass NSTreeController would I just override the add, addChild, to get the right thing to happen? And what could I mess up? I can't seem to find any guidance on this, although I've spent a long time looking. Thanks. John V

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• Is it legal to extend the Class class?

  - by spiralganglion

  I've been writing a system that generates some templates, and then generates some objects based on those templates. I had the idea that the templates could be extensions of the Class class, but that resulted in some magnificent errors: VerifyError: Error #1107: The ABC data is corrupt, attempt to read out of bounds. What I'm wondering is if subclassing Class is even possible, if there is perhaps some case where doing this would be appropriate, and not just a gross misuse of OOP. I believe it should be possible, as ActionScript allows you to create variables of the Class type. This use is described in the LiveDocs entry for Class, yet I've seen no mentions of subclassing Class. Here's a pseudocode example: class Foo extends Class var a:Foo = new Foo(); trace(a is Class) // true, right? var b = new a(); I have no idea what the type of b would be. In summary: can you subclass the Class class? If so, how can you do it without errors, and what type are the instances of the instances of the Class subclass?

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• Objective-C: Getting the True Class of Classes in Class Clusters

  - by TechZen

  Recently while trying to answer a questions here, I ran some test code to see how Xcode/gdb reported the class of instances in class clusters. (see below) In the past, I've expected to see something like: PrivateClusterClass:PublicSuperClass:NSObject Such as this (which still returns as expected): NSPathStore2:NSString:NSObject ... for a string created with +[NSString pathWithComponents:]. However, with NSSet and subclass the following code: - (void)applicationDidFinishLaunching:(UIApplication *)application { NSSet *s=[NSSet setWithObject:@"setWithObject"]; NSMutableSet *m=[NSMutableSet setWithCapacity:1]; [m addObject:@"Added String"]; NSMutableSet *n = [[NSMutableSet alloc] initWithCapacity:1]; [self showSuperClasses:s]; [self showSuperClasses:m]; [self showSuperClasses:n]; [self showSuperClasses:@"Steve"]; } - (void) showSuperClasses:(id) anObject{ Class cl = [anObject class]; NSString *classDescription = [cl description]; while ([cl superclass]) { cl = [cl superclass]; classDescription = [classDescription stringByAppendingFormat:@":%@", [cl description]]; } NSLog(@"%@ classes=%@",[anObject class], classDescription); } ... outputs: // NSSet *s NSCFSet classes=NSCFSet:NSMutableSet:NSSet:NSObject //NSMutableSet *m NSCFSet classes=NSCFSet:NSMutableSet:NSSet:NSObject //NSMutableSet *n NSCFSet classes=NSCFSet:NSMutableSet:NSSet:NSObject // NSString @"Steve" NSCFString classes=NSCFString:NSMutableString:NSString:NSObject The debugger shows the same class for all Set instances. I know that in the past the Set class cluster did not return like this. What has changed? (I suspect it is a change in the bridge from Core Foundation.) What class cluster report just a generic class e.g. NSCFSet and which report an actual subclass e.g. NSPathStore2? Most importantly, when debugging how do you determine the actual class of a NSSet cluster instance?

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• Interface vs Abstract Class (general OO)

  - by Kave

  Hi, I have had recently two telephone interviews where I've been asked about the differences between an Interface and an Abstract class. I have explained every aspect of them I could think of, but it seems they are waiting for me to mention something specific, and I dont know what it is. From my experience I think the following is true, if i am missing a major point please let me know: Interface: Every single Method declared in an Interface will have to be implemented in the subclass. Only Events, Delegates, Properties (C#) and Methods can exist in a Interface. A class can implement multiple Interfaces. Abstract Class Only Abstract methods have to be implemented by the subclass. An Abstract class can have normal methods with implementations. Abstract class can also have class variables beside Events, Delegates, Properties and Methods. A class can only implement one abstract class only due non-existence of Multi-inheritance in C#. 1) After all that the interviewer came up with the question What if you had an Abstract class with only abstract methods, how would that be different from an interface? I didnt know the answer but I think its the inheritance as mentioned above right? 2) An another interviewer asked me what if you had a Public variable inside the interface, how would that be different than in Abstract Class? I insisted you can't have a public variable inside an interface. I didn't know what he wanted to hear but he wasn't satisfied either. Many Thanks for clarification, Kave See Also: When to use an interface instead of an abstract class and vice versa Interfaces vs. Abstract Classes How do you decide between using an Abstract Class and an Interface?

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• How can I make a family of singletons?

  - by Jay

  I want to create a set of classes that share a lot of common behavior. Of course in OOP when you think that you automatically think "abstract class with subclasses". But among the things I want these classes to do is to each have a static list of instances of the class. The list should function as sort of a singleton within the class. I mean each of the sub-classes has a singleton, not that they share one. "Singleton" to that subclass, not a true singleton. But if it's a static, how can I inherit it? Of course code like this won't work: public abstract A { static List<A> myList; public static List getList() { if (myList==null) myList=new ArrayList<A>(10); return myList; } public static A getSomethingFromList() { List listInstance=getList(); ... do stuff with list ... } public int getSomethingFromA() { ... regular code acting against current instance ... } } public class A1 extends A { ... } public class A2 extends A { ... } A1 somethingfromA1List=(A1) A1.getSomethingFromList(); A2 somethingfromA2List=(A2) A2.getSomethingFromList(); The contents of the list for each subclass would be different, but all the code to work on the lists would be the same. The problem with the above code is that I'd only have one list for all the subclasses, and I want one for each. Yes, I could replicate the code to declare the static list in each of the subclasses, but then I'd also have to replicate all the code that adds to the lists and searches the list, etc, which rather defeats the purpose of subclassing. Any ideas on how to do this without replicating code?

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• NHibernate / Fluent - Mapping multiple objects to single lookup table

  - by Al

  Hi all I am struggling a little in getting my mapping right. What I have is a single self joined table of look up values of certain types. Each lookup can have a parent, which can be of a different type. For simplicities sake lets take the Country and State example. So the lookup table would look like this: Lookups Id Key Value LookupType ParentId - self joining to Id base class public class Lookup : BaseEntity { public Lookup() {} public Lookup(string key, string value) { Key = key; Value = value; } public virtual Lookup Parent { get; set; } [DomainSignature] [NotNullNotEmpty] public virtual LookupType LookupType { get; set; } [NotNullNotEmpty] public virtual string Key { get; set; } [NotNullNotEmpty] public virtual string Value { get; set; } } The lookup map public class LookupMap : IAutoMappingOverride<DBLookup> { public void Override(AutoMapping<Lookup> map) { map.Table("Lookups"); map.References(x => x.Parent, "ParentId").ForeignKey("Id"); map.DiscriminateSubClassesOnColumn<string>("LookupType").CustomType(typeof(LookupType)); } } BASE SubClass map for subclasses public class BaseLookupMap : SubclassMap where T : DBLookup { protected BaseLookupMap() { } protected BaseLookupMap(LookupType lookupType) { DiscriminatorValue(lookupType); Table("Lookups"); } } Example subclass map public class StateMap : BaseLookupMap<State> { protected StateMap() : base(LookupType.State) { } } Now I've almost got my mappings set, however the mapping is still expecting a table-per-class setup, so is expecting a 'State' table to exist with a reference to the states Id in the Lookup table. I hope this makes sense. This doesn't seem like an uncommon approach when wanting to keep lookup-type values configurable. Thanks in advance. Al

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• Subclassing ViewPager Breaks Animation

  - by Ryan Thomas

  In my Android application I have an activity which uses a view pager to display 4+ pages (Fragments). I implemented buttons on each screen that move between pages by calling: pager.setCurrentItem(position, true); The view pager and fragments are all working as I desired. I then began looking for a solution to disable user swiping between pages so that the transition between pages in handled by the buttons only. The solution I found was mentioned in a few stackoverflow articles as well as This Blog that suggest subclassing the view pager to intercept touch events to disable swiping. I followed those examples by subclassing the view pager class as follows: public class ViewPager extends android.support.v4.view.ViewPager { private boolean enabled; public ViewPager(Context context, AttributeSet attrs) { super(context, attrs); this.enabled = true; } @Override public boolean onTouchEvent(MotionEvent event) { if (this.enabled) { return super.onTouchEvent(event); } return false; } @Override public boolean onInterceptTouchEvent(MotionEvent event) { if (this.enabled) { return super.onInterceptTouchEvent(event); } return false; } public void setSwipingEnabled(boolean enabled) { this.enabled = enabled; } } Using the subclassed view pager and calling setSwipingEnabled(false) works as was desired. The user can no longer move between pages with swipe gestures and I can still move between pages via button clicks by calling setCurrentItem(int position, boolean smoothScroll). However using the subclass breaks the animation between pages. When I call setCurrentItem(position, true) with android.support.v4.view.ViewPager I get very clean scrolling animations between pages. When I make the same call using the subclass the screen has a very brief 'flash' and then automatically draws the new page. I would like to know how to fix the animation while retaining the ability to disable user swiping between pages. I greatly appreciate any help with this. Let me know if you need any additional information. So far I have tested using a Samsung device running 2.3.5 and an AVD emulator targeting Android 2.3.3.

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• Which is better Java programming practice: stacking enums and enum constructors, or subclassing?

  - by Arvanem

  Hi folks, Given a finite number of items which differ in kind, is it better to represent them with stacked enums and enum constructors, or to subclass them? Or is there a better approach altogether? To give you some context, in my small RPG program (which ironically is supposed to be simple), a character has different kinds of items in his or her inventory. Items differ based on their type and use and effect. For example, one item of inventory is a spell scroll called Gremlin that adjusts the Utility attribute. Another item might be a sword called Mort that is used in combat and inflicts damage. In my RPG code, I now have tried two ways of representing inventory items. One way was subclassing (for example, InventoryItem - Spell - AdjustingAttributes; InventoryItem - Weapon - Sword) and instantiating each subclass when needed, and assigning values such as names like Gremlin and Mort. The other way was by stacking enums and enum constructors. For example, I created enums for itemCategory and itemSpellTypes and itemWeaponTypes, and the InventoryItem enum was like this: public enum InventoryItem { GREMLIN(itemType.SPELL, itemSpellTypes.ATTRIBUTE, Attribute.UTILITY), MORT(itemType.WEAPON, itemWeaponTypes.SWORD, 30); InventoryItem(itemType typeOfItem, itemSpellTypes spellType, Attribute attAdjusted) { // snip, enum logic here } InventoryItem(itemType typeOfItem, itemWeaponTypes weaponType, int dmg) { // snip, enum logic here } // and so on, for all the permutations of items. } Is there a better Java programming practice than these two approaches? Or if these are the only ways, which of the two is better? Thanks in advance for your suggestions.

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• C++ polymorphism, function calls

  - by moai

  Okay, I'm pretty inexperienced as a programmer, let alone in C++, so bear with me here. What I wanted to do was to have a container class hold a parent class pointer and then use polymorphism to store a child class object. The thing is that I want to call one of the child class's functions through the parent class pointer. Here's a sort of example of what I mean in code: class SuperClass { public: int x; } class SubClass : public SuperClass { public: void function1() { x += 1; } } class Container { public: SuperClass * alpha; Container(SuperClass& beta) { alpha = beta; } } int main() { Container cont = new Container(new SubClass); } (I'm not sure that's right, I'm still really shaky on pointers. I hope it gets the point across, at least.) So, I'm not entirely sure whether I can do this or not. I have a sneaking suspicion the answer is no, but I want to be sure. If someone has another way to accomplish this sort of thing, I'd be glad to hear it.

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• Behavior difference between UIView.subviews and [NSView subviews]

  - by zpasternack

  I have a piece of code in an iPhone app, which removes all subviews from a UIView subclass. It looks like this: NSArray* subViews = self.subviews; for( UIView *aView in subViews ) { [aView removeFromSuperview]; } This works fine. In fact, I never really gave it much thought until I tried nearly the same thing in a Mac OS X app (from an NSView subclass): NSArray* subViews = [self subviews]; for( NSView *aView in subViews ) { [aView removeFromSuperview]; } That totally doesn’t work. Specifically, at runtime, I get this: *** Collection <NSCFArray: 0x1005208a0> was mutated while being enumerated. I ended up doing it like so: NSArray* subViews = [[self subviews] copy]; for( NSView *aView in subViews ) { [aView removeFromSuperview]; } [subViews release]; That's fine. What’s bugging me, though, is why does it work on the iPhone? subviews is a copy property: @property(nonatomic,readonly,copy) NSArray *subviews; My first thought was, maybe @synthesize’d getters return a copy when the copy attribute is specified. The doc is clear on the semantics of copy for setters, but doesn’t appear to say either way for getters (or at least, it’s not apparent to me). And actually, doing a few tests of my own, this clearly does not seem to be the case. Which is good, I think returning a copy would be problematic, for a few reasons. So the question is: how does the above code work on the iPhone? NSView is clearly returning a pointer to the actual array of subviews, and perhaps UIView isn’t. Perhaps it’s simply an implementation detail of UIView, and I shouldn’t get worked up about it. Can anyone offer any insight?

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• Custom UIButton Memory Management in dealloc

  - by ddawber

  I am hoping to clarify the processes going on here. I have created a subclass of UIButton whose init method looks like this: - (id)initWithTitle:(NSString *)title frame:(CGRect)btnFrame { self = [UIButton buttonWithType:UIButtonTypeCustom]; [self setTitle:title forState:UIControlStateNormal]; self.frame = btnFrame; return self; } In my view controller I am creating one of these buttons and adding it as a subview: myButton = [[CustomButton alloc] initWithTitle:@"Title" frame:someFrame]; [self.view addSubview:myButton]; In the view controller's dealloc method I log the retain count of my button: - (void)dealloc { NSLog(@"RC: %d", [myButton retainCount]); //RC = 2 [super dealloc]; NSLog(@"RC: %d", [myButton retainCount]); //RC = 1 } The way I understand it, myButton is not actually retained, even though I invoked it using alloc, because in my subclass I created an autorelease button (using buttonWithType:). In dealloc, does this mean that, when dealloc is called the superview releases the button and its retain count goes down to 1? The button has not yet been autoreleased? Or do I need to get that retain count down to zero after calling [super dealloc]? Cheers.

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