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  • Should I use a metaclass, class decorator, or override the __new__ method?

    - by 007brendan
    Here is my problem. I want the following class to have a bunch of property attributes. I could either write them all out like foo and bar, or based on some other examples I've seen, it looks like I could use a class decorator, a metaclass, or override the __new__ method to set the properties automagically. I'm just not sure what the "right" way to do it would be. class Test(object): def calculate_attr(self, attr): # do calculaty stuff return attr @property def foo(self): return self.calculate_attr('foo') @property def bar(self): return self.calculate_attr('bar')

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  • You are only allowed to have a single MapView in a MapActivity

    - by ProNeticas
    I have a function that shows a map page so I can get the user to choose their current location. But if you run this function twice it crashes the App with the Single MapView in a MapActivity error (i.e. opening that settings view again). public void showMapSetterPage(View v) { Log.i(DEBUG_TAG, "Settings screen, set map center launched"); // Set which view object we fired off from set_pv(v); // Show Map Settings Screen setContentView(R.layout.set_map_center); // Initiate the center point map if (mapView == null) { mapView = (MapView) findViewById(R.id.mapview); } mapView.setLongClickable(true); mapView.setStreetView(true); mapView.setBuiltInZoomControls(false); mapView.setSatellite(false); mapController = mapView.getController(); mapController.setZoom(18); LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE); Location location = lm .getLastKnownLocation(LocationManager.GPS_PROVIDER); int lat = (int) (location.getLatitude() * 1E6); int lng = (int) (location.getLongitude() * 1E6); Log.i(DEBUG_TAG, "The LAT and LONG is: " + lat + " == " + lng); point = new GeoPoint(lat, lng); // mapController.setCenter(point); mapController.animateTo(point); } So I have a button that shows this View and onClick="showMapSetterPage". But if you go back to the settings screen out of the map and click the button again I get this error: 03-06 20:55:54.091: ERROR/AndroidRuntime(28014): Caused by: java.lang.IllegalStateException: You are only allowed to have a single MapView in a MapActivity How can I delete the MapView and recreate it?

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  • Attaching methods to prototype from within constructor function

    - by Matthew Taylor
    Here is the textbook standard way of describing a 'class' or constructor function in JavaScript, straight from the Definitive Guide to JavaScript: function Rectangle(w,h) { this.width = w; this.height = h; } Rectangle.prototype.area = function() { return this.width * this.height; }; I don't like the dangling prototype manipulation here, so I was trying to think of a way to encapsulate the function definition for area inside the constructor. I came up with this, which I did not expect to work: function Rectangle(w,h) { this.width = w; this.height = h; this.constructor.prototype.area = function() { return this.width * this.height; }; } I didn't expect this to work because the this reference inside the area function should be pointing to the area function itself, so I wouldn't have access to width and height from this. But it turns out I do! var rect = new Rectangle(2,3); var area = rect.area(); // great scott! it is 6 Some further testing confirmed that the this reference inside the area function actually was a reference to the object under construction, not the area function itself. function Rectangle(w,h) { this.width = w; this.height = h; var me = this; this.constructor.prototype.whatever = function() { if (this === me) { alert ('this is not what you think');} }; } Turns out the alert pops up, and this is exactly the object under construction. So what is going on here? Why is this not the this I expect it to be?

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  • Java: using generic wildcards with subclassing

    - by gibberish
    Say I have a class Foo, a class A and some subclass B of A. Foo accepts A and its sublclasses as the generic type. A and B both require a Foo instance in their constructor. I want A's Foo to be of type A , and B's Foo to be of type B or a superclass of B. So in effect, So I only want this: Foo<X> bar = new Foo<X>; new B(bar); to be possible if X is either A, B, or a both subclass of A and superclass of B. So far this is what I have: class Foo<? extends A>{ //construct } class A(Foo<A> bar){ //construct } class B(Foo<? super B> bar){ super(bar); //construct } The call to super(...) doesn't work, because <A> is stricter than <? super B>. Is it somehow possible to use the constructor (or avoid code duplication by another means) while enforcing these types? Edit: Foo keeps a collection of elements of the generic parameter type, and these elements and Foo have a bidirectional link. It should therefore not be possible to link an A to a Foo.

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  • Using member variables inherited from a templated base class (C++)

    - by Aaron Becker
    I'm trying to use member variables of a templated base class in a derived class, as in this example: template <class dtype> struct A { int x; }; template <class dtype> struct B : public A<dtype> { void test() { int id1 = this->x; // always works int id2 = A<dtype>::x; // always works int id3 = B::x; // always works int id4 = x; // fails in gcc & clang, works in icc and xlc } }; gcc and clang are both very picky about using this variable, and require either an explicit scope or the explicit use of "this". With some other compilers (xlc and icc), things work as I would expect. Is this a case of xlc and icc allowing code that's not standard, or a bug in gcc and clang?

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  • Apples, oranges, and pointers to the most derived c++ class

    - by Matthew Lowe
    Suppose I have a bunch of fruit: class Fruit { ... }; class Apple : public Fruit { ... }; class Orange: public Fruit { ... }; And some polymorphic functions that operate on said fruit: void Eat(Fruit* f, Pesticide* p) { } void Eat(Apple* f, Pesticide* p) { ingest(f,p); } void Eat(Orange* f, Pesticide* p) { peel(f,p); ingest(f,p); } OK, wait. Stop right there. Note at this point that any sane person would make Eat() a virtual member function of the Fruit classes. But that's not an option, because I am not a sane person. Also, I don't want that Pesticide* in the header file for my fruit class. Sadly, what I want to be able to do next is exactly what member functions and dynamic binding allow: typedef list<Fruit*> Fruits; Fruits fs; ... for(Fruits::iterator i=fs.begin(), e=fs.end(); i!=e; ++i) Eat(*i); And obviously, the problem here is that the pointer we pass to Eat() will be a Fruit*, not an Apple* or an Orange*, therefore nothing will get eaten and we will all be very hungry. So what I really want to be able to do instead of this: Eat(*i); is this: Eat(MAGIC_CAST_TO_MOST_DERIVED_CLASS(*i)); But to my limited knowledge, such magic does not exist, except possibly in the form of a big nasty if-statement full of calls to dynamic_cast. So is there some run-time magic of which I am not aware? Or should I implement and maintain a big nasty if-statement full of dynamic_casts? Or should I suck it up, quit thinking about how I would implement this in Ruby, and allow a little Pesticide to make its way into my fruit header?

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  • django access to parent

    - by SledgehammerPL
    model: class Product(models.Model): name = models.CharField(max_length = 128) (...) def __unicode__(self): return self.name class Receipt(models.Model): name = models.CharField(max_length=128) (...) components = models.ManyToManyField(Product, through='ReceiptComponent') def __unicode__(self): return self.name class ReceiptComponent(models.Model): product = models.ForeignKey(Product) receipt = models.ForeignKey(Receipt) quantity = models.FloatField(max_length=9) unit = models.ForeignKey(Unit) def __unicode__(self): return unicode(self.quantity!=0 and self.quantity or '') + ' ' + unicode(self.unit) + ' ' + self.product.genitive And now I'd like to get list of the most often useable products: ReceiptComponent.objects.values('product').annotate(Count('product')).order_by('-product__count' the example result: [{'product': 3, 'product__count': 5}, {'product': 6, 'product__count': 4}, {'product': 5, 'product__count': 3}, {'product': 7, 'product__count': 2}, {'product': 1, 'product__count': 2}, {'product': 11, 'product__count': 1}, {'product': 8, 'product__count': 1}, {'product': 4, 'product__count': 1}, {'product': 9, 'product__count': 1}] It's almost what I need. But I'd prefer having Product object not product value, because I'd like to use this in views.py for generating list.

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  • Python, invoke super constructor

    - by Mike
    class A: def __init__(self): print "world" class B(A): def __init__(self): print "hello" B() hello In all other languages I've worked with the super constructor is invoked implicitly. How does one invoke it in Python? I would expect super(self) but this doesn't work

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  • C++ superclass constructor calling rules

    - by levik
    What are the C++ rules for calling the superclass constructor from a subclass one?? For example I know in Java, you must do it as the first line of the subclass constructor (and if you don't an implicit call to a no-arg super constructor is assumed - giving you a compile error if that's missing).

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  • Delegate Methods Not Firing on Search Results Table

    - by Slinky
    All, I have a UITableView w/detail, with a Search bar, created from code. Works fine on selected items except it doesn't work when an item is clicked from the search results; no delegate methods fire. Never seen this type of behavior before so I don't know where the issue lies. I get the same behavior with standard table cells as well as custom table cells. Appreciate any guidance on this and thanks. Just Hangs Here //ViewController.h @interface SongsViewController : UITableViewController <UISearchBarDelegate,UISearchDisplayDelegate> { NSMutableArray *searchData; UISearchBar *searchBar; UISearchDisplayController *searchDisplayController; UITableViewCell *customSongCell; } //ViewController.m -(void)viewDidLoad { [super viewDidLoad]; CGRect screenRect = [[UIScreen mainScreen] bounds]; CGFloat screenWidth = screenRect.size.width; searchBar = [[UISearchBar alloc] initWithFrame:CGRectMake(0, 0, screenWidth, 88)]; [searchBar setShowsScopeBar:YES]; [searchBar setScopeButtonTitles:[[NSArray alloc] initWithObjects:@"Title",@"Style", nil]]; searchDisplayController = [[UISearchDisplayController alloc] initWithSearchBar:searchBar contentsController:self]; searchDisplayController.delegate = self; searchDisplayController.searchResultsDataSource = self; self.tableView.tableHeaderView = searchBar; //Load custom table cell UINib *songCellNib = [UINib nibWithNibName:@"SongItem" bundle:nil]; //Register this nib, which contains the cell [[self tableView] registerNib:songCellNib forCellReuseIdentifier:@"SongItemCell"]; // create a filtered list that will contain products for the search results table. SongStore *ps = [SongStore defaultStore]; NSArray *songObjects = [ps allSongs]; self.filteredListContent = [NSMutableArray arrayWithCapacity: [songObjects count]]; self.masterSongArr = [[NSMutableArray alloc] initWithArray:[ps allSongs]]; [self refreshData]; [self.tableView reloadData]; self.tableView.scrollEnabled = YES; }

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  • Where in the standard is forwarding to a base class required in these situations?

    - by pgast
    Maybe even better is: Why does the standard require forwarding to a base class in these situations? (yeah yeah yeah - Why? - Because.) class B1 { public: virtual void f()=0; }; class B2 { public: virtual void f(){} }; class D : public B1,public B2{ }; class D2 : public B1,public B2{ public: using B2::f; }; class D3 : public B1,public B2{ public: void f(){ B2::f(); } }; D d; D2 d2; D3 d3; EDG gives: sourceFile.cpp sourceFile.cpp(24) : error C2259: 'D' : cannot instantiate abstract class due to following members: 'void B1::f(void)' : is abstract sourceFile.cpp(6) : see declaration of 'B1::f' sourceFile.cpp(25) : error C2259: 'D2' : cannot instantiate abstract class due to following members: 'void B1::f(void)' : is abstract sourceFile.cpp(6) : see declaration of 'B and similarly for the MS compiler. I might buy the first case,D. But in D2 - f is unambiguously defined by the using declaration, why is that not enough for the compiler to be required to fill out the vtable? Where in the standard is this situation defined?

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  • PHP: How to Pass child class __construct() arguments to parent::__construct() ?

    - by none
    I have a class in PHP like so: class ParentClass { function __construct($arg) { // Initialize a/some variable(s) based on $arg } } It has a child class, as such: class ChildClass extends ParentClass { function __construct($arg) { // Let the parent handle construction. parent::__construct($arg); } } What if, for some reason, the ParentClass needs to change to take more than one optional argument, which I would like my Child class to provide "just in case"? Unless I re-code the ChildClass, it will only ever take the one argument to the constructor, and will only ever pass that one argument. Is this so rare or such a bad practice that the usual case is that a ChildClass wouldn't need to be inheriting from a ParentClass that takes different arguments? Essentially, I've seen in Python where you can pass a potentially unknown number of arguments to a function via somefunction(*args) where 'args' is an array/iterable of some kind. Does something like this exist in PHP? Or should I refactor these classes before proceeding?

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  • Java method: retrieve the inheriting type

    - by DrDro
    I have several classes that extend C and I would need a method that accepts any argument of type C. But in this method I would like to know if I'm dealing with A or B. * public A extends C public B extends C public void goForIt(C c)() If I cast how can I retrieve the type in a clean way (I just read using getClass or instanceof is often not the best way). *Sorry but I can't type closing braces

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  • How to combine two separate unrelated Git repositories into one with single history timeline

    - by Antony
    I have two unrelated (not sharing any ancestor check in) Git repositories, one is a super repository which consists a number of smaller projects (Lets call it repository A). Another one is just a makeshift local Git repository for a smaller project (lets call it repository B). Graphically, it would look like this A0-B0-C0-D0-E0-F0-G0-HEAD (repo A) A0-B0-C0-D0-E0-F0-G0-HEAD (remote/master bare repo pulled & pushed from repo A) A1-B1-C1-D1-E1-HEAD (repo B) Ideally, I would really like to merge repo B into repo A with a single history timeline. So it would appear that I originally started project in repo A. Graphically, this would be the ideal end result A0-A1-B1-B0-D1-C0-D0-E0-F0-G0-E1-H(from repo B)-HEAD (new repo A) A0-A1-B1-B0-D1-C0-D0-E0-F0-G0-E1-H(from repo B)-HEAD (remote/master bare repo pulled & pushed from repo A) I have been doing some reading with submodules and subtree (Pro Git is a pretty good book by the way), but both of them seem to cater solution towards maintaining two separate branch with sub module being able to pull changes from upstream and subtree being slightly less headache. Both solution require additional and specialized git commands to handle check ins and sync between master and sub tree/module branch. Both solution also result in multiple time-lines (with --squash you even get 3 timelines with subtree). The closest solution from SO seems to talk about "graft", but is that really it? The goal is to have a single unified repository where I can pull/push check-ins, so that there are no more repo B, just repo A in the end.

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  • are there requirements for Struts setters beyond variable name matching?

    - by slk
    I have a model-driven Struts Web action: public class ModelDrivenAction<T extends Object> implements ModelDriven<T>, Preparable { protected Long id; protected T model; @Override public void prepare() {} public void setId(Long id) { this.id = id; } @Override public T getModel() { return model; } public void setModel(T model) { this.model = model; } } I have another action which is not currently model-driven: public class OtherAction implements Preparable { private ModelObj modelObj; private Long modelId; @Override public void prepare() { modelObj = repoService.retrieveModelById(modelId); } public void setModelId(Long modelId) { this.modelId = modelId; } } I wish to make it so, and would like to avoid having to track down all the instances in JavaScript where the action is passed a "modelId" parameter instead of "id" if at all possible. I thought this might work, so either modelId or id could be passed in: public class OtherAction extends ModelDrivenAction<ModelObj> { @Override public void prepare() { model = repoService.retrieveModelById(id); } public void setModelId(Long modelId) { this.id = modelId; } } However, server/path/to/other!method?modelId=123 is failing to set id. I thought so long as a setter matched a parameter name the Struts interceptor would call it on action invocation. Am I missing something here?

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  • Find whether a particular cell of a table has an img tag

    - by SilentPro
    I am generating a table dynamically using Django. The same table template is used to generate a variety of tables depending on the data supplied. In one scenario a particular column contains image tags. Since my table is editable (using jquery) the image cell also becomes editable and removes my content. I want some special behavior on double click of such cells like say upload an image. How do I accomplish this with a jquery? My script for making the table editable is given below. $(function() { $("td").dblclick(function() { var OriginalContent = $(this).text(); $(this).addClass("cellEditing"); $(this).html("<input type='text' value='" + OriginalContent + "' />"); $(this).children().first().focus(); $(this).children().first().keypress(function(e) { if (e.which == 13) { var newContent = $(this).val(); $(this).parent().text(newContent); $(this).parent().removeClass("cellEditing"); } }); $(this).children().first().blur(function() { $(this).parent().text(OriginalContent); $(this).parent().removeClass("cellEditing"); }); }); });

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  • flex data provider not working if XML has single node value or less

    - by Rees
    hello, i get this error when i retrieve an XML that only has 1 node (no repeating nodes) and i try to store in an ArrayCollection. -When I have MORE than 1 "name" nodes...i do NOT get an error. My test show that XMLListCollection does NOT work either. TypeError: Error #1034: Type Coercion failed: cannot convert "XXXXXX" to mx.collections.ArrayCollection. this error occurs as the line of code: myList= e.result.list.name; Why can't ArrayCollection work with a single node? I'm using this ArrayCollection as a dataprovider for a Component -is there an alternative I can use that will take BOTH single and repeating nodes as well as work as a dataprovider? Thanks in advance! code: [Bindable] private var myList:ArrayCollection= new ArrayCollection(); private function getList(e:Event):void{ var getStudyLoungesService:HTTPService = new HTTPService(); getStuffService.url = "website.com/asdf.php"; getStuffService.addEventListener(ResultEvent.RESULT, onGetList); getStuffService.send(); } private function onGetList(e:ResultEvent):void{ myList= e.result.list.name; }

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  • Saving tags into a database table in CakePHP

    - by Cameron
    I have the following setup for my CakePHP app: Posts id title content Topics id title Topic_Posts id topic_id post_id So basically I have a table of Topics (tags) that are all unique and have an id. And then they can be attached to post using the Topic_Posts join table. When a user creates a new post they will fill in the topics by typing them in to a textarea separated by a comma which will then save these into the Topics table if they do not already exist and then save the references into the Topic_posts table. I have the models set up like so: Post model: class Post extends AppModel { public $name = 'Post'; public $hasAndBelongsToMany = array( 'Topic' => array('with' => 'TopicPost') ); } Topic model: class Topic extends AppModel { public $hasMany = array( 'TopicPost' ); } TopicPost model: class TopicPost extends AppModel { public $belongsTo = array( 'Topic', 'Post' ); } And for the New post method I have this so far: public function add() { if ($this->request->is('post')) { //$this->Post->create(); if ($this->Post->saveAll($this->request->data)) { // Redirect the user to the newly created post (pass the slug for performance) $this->redirect(array('controller'=>'posts','action'=>'view','id'=>$this->Post->id)); } else { $this->Session->setFlash('Server broke!'); } } } As you can see I have used saveAll but how do I go about dealing with the Topic data?

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  • Generic Class Vb.net

    - by KoolKabin
    hi guys, I am stuck with a problem about generic classes. I am confused how I call the constructor with parameters. My interface: Public Interface IDBObject Sub [Get](ByRef DataRow As DataRow) Property UIN() As Integer End Interface My Child Class: Public Class User Implements IDBObject Public Sub [Get](ByRef DataRow As System.Data.DataRow) Implements IDBObject.Get End Sub Public Property UIN() As Integer Implements IDBObject.UIN Get End Get Set(ByVal value As Integer) End Set End Property End Class My Next Class: Public Class Users Inherits DBLayer(Of User) #Region " Standard Methods " #End Region End Class My DBObject Class: Public Class DBLayer(Of DBObject As {New, IDBObject}) Public Shared Function GetData() As List(Of DBObject) Dim QueryString As String = "SELECT * ***;" Dim Dataset As DataSet = New DataSet() Dim DataList As List(Of DBObject) = New List(Of DBObject) Try Dataset = Query(QueryString) For Each DataRow As DataRow In Dataset.Tables(0).Rows **DataList.Add(New DBObject(DataRow))** Next Catch ex As Exception DataList = Nothing End Try Return DataList End Function End Class I get error in the starred area of the DBLayer Object. What might be the possible reason? what can I do to fix it? I even want to add New(byval someval as datatype) in IDBObject interface for overloading construction. but it also gives an error? how can i do it? Adding Sub New(ByVal DataRow As DataRow) in IDBObject producess following error 'Sub New' cannot be declared in an interface. Error Produced in DBLayer Object line: DataList.Add(New DBObject(DataRow)) Msg: Arguments cannot be passed to a 'New' used on a type parameter.

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  • (Cocoa) Can I Subclass and Delegate at the same time?

    - by Alvin
    @interface ClassB <ClassADelegate> : ClassA id <ClassBDelegate> delegate; @end As the code says, ClassB subclasses from ClassA and handles the formation protocol of Class A. However, the variable "delegate" will be duplicated. (ClassA also has "delegate") In fact, it can be done without subclassing, but it seems the code is cumbersome, i.e., to use a variable/function of ClassA, I need to write [[ClassB classA] doSomething] instead of [classB doSomething], where doSomething: is a function of ClassA. Are there any tidy way for me to do that?

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  • Constructor Overload Problem in C++ Inherrentance

    - by metdos
    Here my code snippet: class Request { public: Request(void); ……….. } Request::Request(void) { qDebug()<<"Request: "<<"Hello World"; } class LoginRequest :public Request { public: LoginRequest(void); LoginRequest(QDomDocument); …………… } LoginRequest::LoginRequest(void) { qDebug()<<"LoginRequest: "<<"Hello World"; requestType=LOGIN; requestId=-1; } LoginRequest::LoginRequest(QDomDocument doc){ qDebug()<<"LoginRequest: "<<"Hello World with QDomDocument"; LoginRequest::LoginRequest(); xmlDoc_=doc; } When call constructor of Overrided LoginRequest LoginRequest *test=new LoginRequest(doc); I came up with this result: Request: Hello World LoginRequest: Hello World with QDomDocument Request: Hello World LoginRequest: Hello World Obviously both constructor of LoginRequest called REquest constructor. Is there any way to cape with this situation? I can construct another function that does the job I want to do and have both constructors call that function. But I wonder is there any solution?

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  • Me As Child Type In General Function

    - by Steven
    I have a MustInherit Parent class with two Child classes which Inherit from the Parent. How can I use (or Cast) Me in a Parent function as the the child type of that instance? EDIT: My actual goal is to be able to serialize (BinaryFormatter.Serialize(Stream, Object)) either of my child classes. However, "repeating the code" in each child "seems" wrong. EDIT2: This is my Serialize function. Where should I implement this function? Copying and pasting to each child doesn't seem right, but casting the parent to a child doesn't seem right either. Public Function Serialize() As Byte() Dim bFmt As New BinaryFormatter() Dim mStr As New MemoryStream() bFmt.Serialize(mStr, Me) Return mStr.ToArray() End Function

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