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  • c++ constructors

    - by aharont
    i wrote this code: class A { public: A(){d=2.2;cout<<d;} A(double d):d(d){cout<<d;} double getD(){return d;} private: double d; }; class Bing { public: Bing(){a=A(5.3);} void f(){cout<<a.getD();} private: A a; }; int main() { Bing b; b.f(); } i get the output: 2.2 5.3 5.3 instead of 5.3 5.3. it's something in the constructor.... wahy am i getting this? how can i fix it?

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  • can constructors actually return Strings?

    - by elwynn
    Hi all, I have a class called ArionFileExtractor in a .java file of the same name. public class ArionFileExtractor { public String ArionFileExtractor (String fName, String startText, String endText) { String afExtract = ""; // Extract string from fName into afExtract in code I won't show here return afExtract; } However, when I try to invoke ArionFileExtractor in another .java file, as follows: String afe = ArionFileExtractor("gibberish.txt", "foo", "/foo"); NetBeans informs me that there are incompatible types and that java.lang.String is required. But I coded ArionFileExtractor to return the standard string type, which is java.lang.string. I am wondering, can my ArionFileExtractor constructor legally return a String? I very much appreciate any tips or pointers on what I'm doing wrong here.

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  • Use of .apply() with 'new' operator. Is this possible?

    - by Premasagar
    In JavaScript, I want to create an object instance (via the new operator), but pass an arbitrary number of arguments to the constructor. Is this possible? What I want to do is something like this (but the code below does not work): function Something(){ // init stuff } function createSomething(){ return new Something.apply(null, arguments); } var s = createSomething(a,b,c); // 's' is an instance of Something The Answer From the responses here, it became clear that there's no in-built way to call .apply() with the new operator. However, people suggested a number of really interesting solutions to the problem. My preferred solution was this one from Matthew Crumley (I've modified it to pass the arguments property): var createSomething = (function() { function F(args) { return Something.apply(this, args); } F.prototype = Something.prototype; return function() { return new F(arguments); } })();

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  • How to get an array to work with oops concepts in Perl

    - by superstar
    Hello guys, I need some help regarding the arrays in Perl This is the constructor i have. sub new { my $class = shift; my @includeobjects = (); my @excludeobjects = (); my $Packet = { _PacketName => shift, _Platform => shift, _Version => shift, @_IncludePath => @includeobjects, }; bless $Packet, $class; return $Packet; } sub SetPacketName { my ( $Packet, $PacketName ) = @_; $Packet->{_PacketName} = $PacketName if defined($PacketName); return $Packet->{_PacketName}; } sub SetIncludePath { my ( $Packet, @IncludePath ) = @_; $Packet->{@_IncludePath} = @IncludePath; return $Packet->{@_IncludePath}; } sub GetPacketName { my( $Packet ) = @_; return $Packet->{_PacketName}; } sub GetIncludePath { my( $Packet ) = @_; return $Packet->{@_IncludePath}; } The get and set methods work fine for PacketName. But since IncludePath is an array, I could not get it work. The declaration is what i am not able to get right Any suggestions please...

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  • How to create a Binary Tree from a General Tree?

    - by mno4k
    I have to solve the following constructor for a BinaryTree class in java: BinaryTree(GeneralTree<T> aTree) This method should create a BinaryTree (bt) from a General Tree (gt) as follows: Every Vertex from gt will be represented as a leaf in bt. If gt is a leaf, then bt will be a leaf with the same value as gt If gt is not a leaf, then bt will be constructed as an empty root, a left subTree (lt) and a right subTree (lr). Lt is a stric binary tree created from the oldest subtree of gt (the left-most subtree) and lr is a stric binary tree created from gt without its left-most subtree. The frist part is trivial enough, but the second one is giving me some trouble. I've gotten this far: public BinaryTree(GeneralTree<T> aTree){ if (aTree.isLeaf()){ root= new BinaryNode<T>(aTree.getRootData()); }else{ root= new BinaryNode<T>(null); // empty root LinkedList<GeneralTree<T>> childs = aTree.getChilds(); // Childs of the GT are implemented as a LinkedList of SubTrees child.begin(); //start iteration trough list BinaryTree<T> lt = new BinaryTree<T>(childs.element(0)); // first element = left-most child this.addLeftChild(lt); aTree.DeleteChild(hijos.elemento(0)); BinaryTree<T> lr = new BinaryTree<T>(aTree); this.addRightChild(lr); } } Is this the right way? If not, can you think of a better way to solve this? Thank you!

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  • safe placement new & explicit destructor call

    - by uray
    this is an example of my codes: ` template <typename T> struct MyStruct { T object; } template <typename T> class MyClass { MyStruct<T>* structPool; size_t structCount; MyClass(size_t count) { this->structCount = count; this->structPool = new MyStruct<T>[count]; for( size_t i=0 ; i<count ; i++ ) { //placement new to call constructor new (&this->structPool[i].object) T(); } } ~MyClass() { for( size_t i=0 ; i<this->structCount ; i++ ) { //explicit destructor call this->structPool[i].object.~T(); } delete[] this->structPool; } } ` my question is, is this a safe way to do? do I make some hidden mistake at some condition? will it work for every type of object (POD and non-POD) ?

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  • How do I use an array as an object attribute in Perl?

    - by superstar
    Hello guys, I need some help regarding the arrays in Perl This is the constructor i have. sub new { my $class = shift; my @includeobjects = (); my @excludeobjects = (); my $Packet = { _PacketName => shift, _Platform => shift, _Version => shift, @_IncludePath => @includeobjects, }; bless $Packet, $class; return $Packet; } sub SetPacketName { my ( $Packet, $PacketName ) = @_; $Packet->{_PacketName} = $PacketName if defined($PacketName); return $Packet->{_PacketName}; } sub SetIncludePath { my ( $Packet, @IncludePath ) = @_; $Packet->{@_IncludePath} = @IncludePath; return $Packet->{@_IncludePath}; } sub GetPacketName { my( $Packet ) = @_; return $Packet->{_PacketName}; } sub GetIncludePath { my( $Packet ) = @_; return $Packet->{@_IncludePath}; } The get and set methods work fine for PacketName. But since IncludePath is an array, I could not get it work. The declaration is what I am not able to get right.

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  • Is there a good way to copy a Gtk widget?

    - by Jake
    Is there a way, using the Gtk library in C, to clone a Gtk button (for instance), and pack it somewhere else in the app. I know you can't pack the same widget twice. And that this code obviously wouldn't work, but shows what happens when I attempt a shallow copy of the button: GtkButton *a = g_object_new(GTK_TYPE_BUTTON, "label", "o_0", NULL); GtkButton *b = g_memdup(b, sizeof *b); gtk_box_pack_start_defaults(GTK_BOX(vbox), GTK_WIDGET(b)); There is surrounding code which creates a vbox and packs it in a window and runs gtk_main(). This will result in these hard to understand error messages: (main:6044): Gtk-CRITICAL **: gtk_widget_hide: assertion `GTK_IS_WIDGET (widget)' failed (main:6044): Gtk-CRITICAL **: gtk_widget_realize: assertion `GTK_WIDGET_ANCHORED (widget) || GTK_IS_INVISIBLE (widget)' failed ** Gtk:ERROR:/build/buildd/gtk+2.0-2.18.3/gtk/gtkwidget.c:8431:gtk_widget_real_map: assertion failed: (GTK_WIDGET_REALIZED (widget)) Along the same lines, if I were to write my own GObject (not necessarily a Gtk widget), is there a good way to write a copy constructor. Im thinking it should be an interface with optional hooks and based mostly on the properties, handling the class's hierarchy in some way. I'd want to do this: GtkButton *b = copyable_copy(COPYABLE(a)); If GtkButton could use a theoretical copyable interface.

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  • Freestanding ARM C++ Code - empty .ctors section

    - by Matthew Iselin
    I'm writing C++ code to run in a freestanding environment (basically an ARM board). It's been going well except I've run into a stumbling block - global static constructors. To my understanding the .ctors section contains a list of addresses to each static constructor, and my code simply needs to iterate this list and make calls to each function as it goes. However, I've found that this section in my binary is in fact completely empty! Google pointed towards using ".init_array" instead of ".ctors" (an EABI thing), but that has not changed anything. Any ideas as to why my static constructors don't exist? Relevant linker script and objdump output follows: .ctors : { . = ALIGN(4096); start_ctors = .; *(.init_array); *(.ctors); end_ctors = .; } .dtors : { . = ALIGN(4096); start_dtors = .; *(.fini_array); *(.dtors); end_dtors = .; } -- 2 .ctors 00001000 8014c000 8014c000 00054000 2**2 CONTENTS, ALLOC, LOAD, DATA <snip> 8014d000 g O .ctors 00000004 start_ctors <snip> 8014d000 g O .ctors 00000004 end_ctors I'm using an arm-elf targeted GCC compiler (4.4.1).

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  • CArray doesn't call copy constructors on memory reallocations, now what?

    - by MMx
    Suppose I have a class that requires copy constructor to be called to make a correct copy of: struct CWeird { CWeird() { number = 47; target = &number; } CWeird(const CWeird &other) : number(other.number), target(&number) { } void output() { printf("%d %d\n", *target, number); } int *target, number; }; Now the trouble is that CArray doesn't call copy constructors on its elements when reallocating memory (only memcpy from the old memory to the new), e.g. this code CArray<CWeird> a; a.SetSize(1); a[0].output(); a.SetSize(2); a[0].output(); results in 47 47 -572662307 47 I don't get this. Why is it that std::vector can copy the same objects properly and CArray can't? What's the lesson here? Should I use only classes that don't require explicit copy constructors? Or is it a bad idea to use CArray for anything serious?

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  • Does code in the constructor add to code in subclass constructors?

    - by Jeremy Rudd
    Does code in the constructor add to code in subclass constructors? Or does the subclass's constructor override the superclass? Given this example superclass constructor: class Car{ function Car(){ trace("CAR") } } ...and this subclass constructor: class FordCar extends Car{ function FordCar(){ trace("FORD") } } When an instance of FordCar is created, will this trace "Car" and "Ford" ??

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  • why we can't initialize a servlet using constructor itself?

    - by Reddy
    Why do we have to override init() method in Servlets while we can do the initialization in the constructor and have web container call the constructor passing ServletConfig reference to servlet while calling constructor? Ofcourse container has to use reflection for this but container has to use reflection anyway to call a simple no-arg constructor

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  • Requriing static class setter to be called before Constructor, bad design?

    - by roverred
    I have a class, say Foo, and every instance of Foo will need and contain the same List object, myList. Since every class instance will share the same List Object, I thought it would be good to make myList static and use a static function to set myList before the constructor is called. I was wondering if this was bad, because this requires the setter to be called before the constructor. If the person doesn't, the program will crash. Alternative way would be passing myList every time. Thanks.

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  • Why can't I get 100% code coverage on a method that calls a constructor of a generic type?

    - by Martin Watts
    Today I came across a wierd issue in a Visual Studio 2008 Code Coverage Analysis. Consider the following method:  private IController GetController<T>(IContext context) where T : IController, new() {     IController controller = new T();     controller.ListeningContext = context;     controller.Plugin = this;     return controller; } This method is called in a unit test as follows (MenuController has an empty constructor): controller = plugin.GetController<MenuController>(null);  After calling this method from a Unit Test, the following code coverage report is generated: As you can see, Code Coverage is only 85%. Looking up the code results in the following: Apparently, the call to the constructor of the generic type is considered only partly covered. WHY? Google didn't help. And MSDN didn't help at all, of course. Anybody who does know?

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  • C++ How to deep copy a struct with unknown datatype?

    - by Ewald Peters
    hi, i have a "data provider" which stores its output in a struct of a certain type, for instance struct DATA_TYPE1{ std::string data_string; }; then this struct has to be casted into a general datatype, i thought about void * or char *, because the "intermediate" object that copies and stores it in its binary tree should be able to store many different types of such struct data. struct BINARY_TREE_ENTRY{ void * DATA; struct BINARY_TREE_ENTRY * next; }; this void * is then later taken by another object that casts the void * back into the (struct DATA_TYPE1 *) to get the original data. so the sender and the receiver know about the datatype DATA_TYPE1 but not the copying object inbetween. but how can the intermidiate object deep copy the contents of the different structs, when it doesn't know the datatype, only void * and it has no method to copy the real contents; dynamic_cast doesn't work for void *; the "intermediate" object should do something like: void store_data(void * CASTED_DATA_STRUCT){ void * DATA_COPY = create_a_deepcopy_of(CASTED_DATA_STRUCT); push_into_bintree(DATA_COPY); } a simple solution would be that the sending object doesn't delete the sent data struct, til the receiving object got it, but the sending objects are dynamically created and deleted, before the receiver got the data from the intermediate object, for asynchronous communication, therefore i want to copy it. instead of converting it to void * i also tried converting to a superclass pointer of which the intermediate copying object knows about, and which is inherited by all the different datatypes of the structs: struct DATA_BASE_OBJECT{ public: DATA_BASE_OBJECT(){} DATA_BASE_OBJECT(DATA_BASE_OBJECT * old_ptr){ std::cout << "this should be automatically overridden!" << std::endl; } virtual ~DATA_BASE_OBJECT(){} }; struct DATA_TYPE1 : public DATA_BASE_OBJECT { public: string str; DATA_TYPE1(){} ~DATA_TYPE1(){} DATA_TYPE1(DATA_TYPE1 * old_ptr){ str = old_ptr->str; } }; and the corresponding binary tree entry would then be: struct BINARY_TREE_ENTRY{ struct DATA_BASE_OBJECT * DATA; struct BINARY_TREE_ENTRY * next; }; and to then copy the unknown datatype, i tried in the class that just gets the unknown datatype as a struct DATA_BASE_OBJECT * (before it was the void *): void * copy_data(DATA_BASE_OBJECT * data_that_i_get_in_the_sub_struct){ struct DATA_BASE_OBJECT * copy_sub = new DATA_BASE_OBJECT(data_that_i_get_in_the_sub_struct); push_into_bintree(copy_sub); } i then added a copy constructor to the DATA_BASE_OBJECT, but if the struct DATA_TYPE1 is first casted to a DATA_BASE_OBJECT and then copied, the included sub object DATA_TYPE1 is not also copied. i then thought what about finding out the size of the actual object to copy and then just memcopy it, but the bytes are not stored in one row and how do i find out the real size in memory of the struct DATA_TYPE1 which holds a std::string? Which other c++ methods are available to deepcopy an unknown datatype (and to maybe get the datatype information somehow else during runtime) thanks Ewald

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  • Cannot find Symbol = new

    - by Nick G.
    Java is complaining! cannot find symbol symbol : constructor Bar() location: class Bar JPanel panel = new Bar(); ^ QUESTION: Why am I getting this error?...everything seems to be correct. this is the coding: public class JFrameWithPanel { public static void main(String[] args) { JPanel panel = new Bar(); } } Bar( ) is public class Bar extends JPanel { public Bar(final JFrame frame) { super(new BorderLayout()); String[] tests = { "A+ Certification", "Network+ Certification", "Security+ Certification", "CIT Full Test Package" }; JComboBox comboBox = new JComboBox(tests); TextArea text = new TextArea(5, 10); add(new JLabel("Welcome to the CIT Test Program ")); add(new JLabel("Please select which Test Package from the list below.")); JMenuBar menuBar = new JMenuBar(); JMenu fileMenu = new JMenu("File"); JMenu editMenu = new JMenu("Edit"); JMenu helpMenu = new JMenu("Help"); menuBar.add(fileMenu); menuBar.add(editMenu); menuBar.add(helpMenu); JMenuItem newMenu = new JMenuItem("New (Ctrl+N)"); JMenuItem openMenu = new JMenuItem("Open (Ctrl+O)"); JMenuItem saveMenu = new JMenuItem("Save (Ctrl+S)"); JMenuItem exitMenu = new JMenuItem("Exit (Ctrl+W)"); JMenuItem cutMenu = new JMenuItem("Cut (Ctrl+X)"); JMenuItem copyMenu = new JMenuItem("Copy (Ctrl+C)"); JMenuItem pasteMenu = new JMenuItem("Paste (Ctrl+V)"); JMenuItem infoMenu = new JMenuItem("Help (Ctrl+H)"); fileMenu.add(newMenu); fileMenu.add(openMenu); fileMenu.add(saveMenu); fileMenu.add(exitMenu); editMenu.add(cutMenu); editMenu.add(copyMenu); editMenu.add(pasteMenu); helpMenu.add(infoMenu); this.add(comboBox, BorderLayout.NORTH); this.add(text, BorderLayout.SOUTH); frame.setJMenuBar(menuBar); add(new JButton("Select") { { addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { frame.dispose(); JOptionPane.showMessageDialog(frame, "IT WORKS!"); } }); } }); } }

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  • C++ keeping a list of objects and calling a contructor through another function

    - by Nona Urbiz
    why isnt my object being created? When I do it like so, I am told error C2065: 'AllReferrals' : undeclared identifier as well as error C2228: left of '.push_back' must have class/struct/union. If I put the list initialization before the class I get error C2065: 'AllReferrals' : undeclared identifier. Thanks! #include <iostream> #include <fstream> #include <regex> #include <string> #include <list> #include <map> using namespace std; using namespace tr1; class Referral { public: string url; map<string, int> keywords; static bool submit(string url, string keyword, int occurrences) { //if(lots of things i'll later add){ Referral(url, keyword, occurrences); return true; //} //else // return false; } private: list<string> urls; Referral(string url, string keyword, int occurrences) { url = url; keywords[keyword] = occurrences; AllReferrals.push_back(this); } }; static list<Referral> AllReferrals; int main() { Referral::submit("url", "keyword", 1); cout << AllReferrals.size(); cout << "\n why does that ^^ say 0 (help me make it say one)?"; cout << "\n and how can i AllReferrals.push_back(this) from my constructor?"; cout << " When I do it like so, I am told error C2065: 'AllReferrals' : undeclared identifier"; cout << " as well as error C2228: left of '.push_back' must have class/struct/union."; cout << " If I put the list initialization before the class I get error C2065: 'AllReferrals' : undeclared identifier."; cout << "\n\n\t Thanks!"; getchar(); }

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  • How to approach copying objects with smart pointers as class attributes?

    - by tomislav-maric
    From the boost library documentation I read this: Conceptually, smart pointers are seen as owning the object pointed to, and thus responsible for deletion of the object when it is no longer needed. I have a very simple problem: I want to use RAII for pointer attributes of a class that is Copyable and Assignable. The copy and assignment operations should be deep: every object should have its own copy of the actual data. Also, RTTI needs to be available for the attributes (their type may also be determined at runtime). Should I be searching for an implementation of a Copyable smart pointer (the data are small, so I don't need Copy on Write pointers), or do I delegate the copy operation to the copy constructors of my objects as shown in this answer? Which smart pointer do I choose for simple RAII of a class that is copyable and assignable? (I'm thinking that the unique_ptr with delegated copy/assignment operations to the class copy constructor and assignment operator would make a proper choice, but I am not sure) Here's a pseudocode for the problem using raw pointers, it's just a problem description, not a running C++ code: // Operation interface class ModelOperation { public: virtual void operate = (); }; // Implementation of an operation called Special class SpecialModelOperation : public ModelOperation { private: // Private attributes are present here in a real implementation. public: // Implement operation void operate () {}; }; // All operations conform to ModelOperation interface // These are possible operation names: // class MoreSpecialOperation; // class DifferentOperation; // Concrete model with different operations class MyModel { private: ModelOperation* firstOperation_; ModelOperation* secondOperation_; public: MyModel() : firstOperation_(0), secondOperation_(0) { // Forgetting about run-time type definition from input files here. firstOperation_ = new MoreSpecialOperation(); secondOperation_ = new DifferentOperation(); } void operate() { firstOperation_->operate(); secondOperation_->operate(); } ~MyModel() { delete firstOperation_; firstOperation_ = 0; delete secondOperation_; secondOperation_ = 0; } }; int main() { MyModel modelOne; // Some internal scope { // I want modelTwo to have its own set of copied, not referenced // operations, and at the same time I need RAII to work for it, // as soon as it goes out of scope. MyModel modelTwo (modelOne); } return 0; }

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  • How does Unity.Resolve know which constructor to use?

    - by stiank81
    Given a class with several constructors - how can I tell Resolve which constructor to use? Consider the following example class: public class Foo { public Foo() { } public Foo(IBar bar) { Bar = bar; } public Foo(string name, IBar bar) { Bar = bar; Name = name; } public IBar Bar { get; set; } public string Name { get; set; } } If I want to create an object of type Foo using Resolve how will Resolve know which constructor to use? And how can I tell it to use the right one? Let's say I have a container with an IBar registered - will it understand that it should favor the constructor taking IBar? And if I specify a string too - will it use the (string, IBar) constructor? Foo foo = unityContainer.Resolve<Foo>(); And please ignore the fact that it would probably be easier if the class just had a single constructor...

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  • Is there ever a reason to do all an object's work in a constructor?

    - by Kane
    Let me preface this by saying this is not my code nor my coworkers' code. Years ago when our company was smaller, we had some projects we needed done that we did not have the capacity for, so they were outsourced. Now, I have nothing against outsourcing or contractors in general, but the codebase they produced is a mass of WTFs. That being said, it does (mostly) work, so I suppose it's in the top 10% of outsourced projects I've seen. As our company has grown, we've tried to take more of our development in house. This particular project landed in my lap so I've been going over it, cleaning it up, adding tests, etc etc. There's one pattern I see repeated a lot and it seems so mindblowingly awful that I wondered if maybe there is a reason and I just don't see it. The pattern is an object with no public methods or members, just a public constructor that does all the work of the object. For example, (the code is in Java, if that matters, but I hope this to be a more general question): public class Foo { private int bar; private String baz; public Foo(File f) { execute(f); } private void execute(File f) { // FTP the file to some hardcoded location, // or parse the file and commit to the database, or whatever } } If you're wondering, this type of code is often called in the following manner: for(File f : someListOfFiles) { new Foo(f); } Now, I was taught long ago that instantiated objects in a loop is generally a bad idea, and that constructors should do a minimum of work. Looking at this code it looks like it would be better to drop the constructor and make execute a public static method. I did ask the contractor why it was done this way, and the response I got was "We can change it if you want". Which was not really helpful. Anyway, is there ever a reason to do something like this, in any programming language, or is this just another submission to the Daily WTF?

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  • What's the proper term for a function inverse to a constructor? Deconstructor, destructor, or something else?

    - by Petr Pudlák
    Edit: I'm rephrasing the question a bit. Apparently I caused some confusion because I didn't realize that the term destructor is used in OOP for something quite different - it's a function invoked when an object is being destroyed. In functional programming we (try to) avoid mutable state so there is no such equivalent to it. (I added the proper tag to the question.) Instead, I've seen that the record field for unwrapping a value (especially for single-valued data types such as newtypes) is sometimes called destructor or perhaps deconstructor. For example, let's have (in Haskell): newtype Wrap = Wrap { unwrap :: Int } Here Wrap is the constructor and unwrap is what? I've seen both, for example: ... Most often, one supplies smart constructors and destructors for these to ease working with them. ... at Haskell wiki, or ... The general theme here is to fuse constructor - deconstructor pairs like ... at Haskell wikibook (here it's probably meant in a bit more general sense). The questions are: How do we call unwrap in functional programming? Deconstructor? Destructor? Or by some other term? And to clarify, is this terminology applicable to other functional languages, or is it used just in the Has

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  • Are injectable classes allowed to have constructor parameters in DI?

    - by Songo
    Given the following code: class ClientClass{ public function print(){ //some code to calculate $inputString $parser= new Parser($inputString); $result= $parser->parse(); } } class Parser{ private $inputString; public __construct($inputString){ $this->inputString=$inputString; } public function parse(){ //some code } } Now the ClientClass has dependency on class Parser. However, if I wanted to use Dependency Injection for unit testing it would cause a problem because now I can't send the input string to the parser constructor like before as its calculated inside ClientCalss itself: class ClientClass{ private $parser; public __construct(Parser $parser){ $this->parser=$parser; } public function print(){ //some code to calculate $inputString $result= $this->parser->parse(); //--> will throw an exception since no string was provided } } The only solution I found was to modify all my classes that took parameters in their constructors to utilize Setters instead (example: setInputString()). However, I think there might be a better solution than this because sometimes modifying existing classes can cause much harm than benefit. So, Are injectable classes not allowed to have input parameters? If a class must take input parameters in its constructor, what would be the way to inject it properly? UPDATE Just for clarification, the problem happens when in my production code I decide to do this: $clientClass= new ClientClass(new Parser($inputString));//--->I have no way to predict $inputString as it is calculated inside `ClientClass` itself. UPDATE 2 Again for clarification, I'm trying to find a general solution to the problem not for this example code only because some of my classes have 2, 3 or 4 parameters in their constructors not only one.

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  • MVVM load data during or after ViewModel construction?

    - by mkmurray
    My generic question is as the title states, is it best to load data during ViewModel construction or afterward through some Loaded event handling? I'm guessing the answer is after construction via some Loaded event handling, but I'm wondering how that is most cleanly coordinated between ViewModel and View? Here's more details about my situation and the particular problem I'm trying to solve: I am using the MVVM Light framework as well as Unity for DI. I have some nested Views, each bound to a corresponding ViewModel. The ViewModels are bound to each View's root control DataContext via the ViewModelLocator idea that Laurent Bugnion has put into MVVM Light. This allows for finding ViewModels via a static resource and for controlling the lifetime of ViewModels via a Dependency Injection framework, in this case Unity. It also allows for Expression Blend to see everything in regard to ViewModels and how to bind them. So anyway, I've got a parent View that has a ComboBox databound to an ObservableCollection in its ViewModel. The ComboBox's SelectedItem is also bound (two-way) to a property on the ViewModel. When the selection of the ComboBox changes, this is to trigger updates in other views and subviews. Currently I am accomplishing this via the Messaging system that is found in MVVM Light. This is all working great and as expected when you choose different items in the ComboBox. However, the ViewModel is getting its data during construction time via a series of initializing method calls. This seems to only be a problem if I want to control what the initial SelectedItem of the ComboBox is. Using MVVM Light's messaging system, I currently have it set up where the setter of the ViewModel's SelectedItem property is the one broadcasting the update and the other interested ViewModels register for the message in their constructors. It appears I am currently trying to set the SelectedItem via the ViewModel at construction time, which hasn't allowed sub-ViewModels to be constructed and register yet. What would be the cleanest way to coordinate the data load and initial setting of SelectedItem within the ViewModel? I really want to stick with putting as little in the View's code-behind as is reasonable. I think I just need a way for the ViewModel to know when stuff has Loaded and that it can then continue to load the data and finalize the setup phase. Thanks in advance for your responses.

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