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  • (this == null) in C#!

    - by SLaks
    Due to a bug that was fixed in C# 4, the following program prints true. (Try it in LINQPad) void Main() { new Derived(); } class Base { public Base(Func<string> valueMaker) { Console.WriteLine(valueMaker()); } } class Derived : Base { string CheckNull() { return "Am I null? " + (this == null); } public Derived() : base(() => CheckNull()) { } } In VS2008 in Release mode, in throws an InvalidProgramException. (In Debug mode, it works fine) In VS2010 Beta 2, it doesn't compile (I didn't try Beta 1); I learned that the hard way Is there any other way to make this == null in pure C#?

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  • wpf treeview does not show child objects

    - by gangt
    I have an object with child object(s) and I load it using linq. And I assign it to a treeView's itemssource. treeView.DisplayMemberPath = "Name"; treeView.ItemsSource = tasks; It shows only the parent nodes (task.name), I couldn't figure out how to add children (TaskItems.name). All the examples show HierarchicalData in xaml. I need to do it in code-behind, just like the above code. Is it possible? public class Task { public int Id; public string Name; public bool IsActive; public List<TaskItem> TaskItems = new List<TaskItem>(); } public class TaskItem { public int TaskId; public string Name; public string Value; } -------------- var tasks1 = from t in xd.Descendants("taskheader") select new Task { Id = (int)t.Element("id"), Name = t.Element("name").Value, IsActive = t.Element("isactive").Value == "1", TaskItems = t.Elements("taskdetail").Select(e => new TaskItem { TaskId = (int)e.Element("taskid"), Name = (string)e.Element("name"), Value = (string)e.Element("value"), }).ToList() }; -------------- List<Task> tasks = new List<Task>(); tasks = tasks1;

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  • Rails: url_for to be available in a isolated class that must be instanced

    - by Totty
    Rails: url_for to be available in a isolated class that must be instanced: class ProfilePresenter < ActionController::Base attr_reader :profile def initialize(profile) super @a = url_for(:controller => 'profiles', :action => 'view', :profile_url => 'dd') @a @profile = profile end end How to make the url_for work? i tried to extend the ActionController::Base and the ActionView::Base and i cant :s

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  • Help me plan larger Qt project

    - by Pirate for Profit
    I'm trying to create an automated task management system for our company, because they pay me to waste my time. New users will create a "profile", which will store all the working data (I guess serialize everything into xml rite?). A "profile" will contain many different tasks. Tasks are basically just standard computer janitor crap such as moving around files, reading/writing to databases, pinging servers, etc.). So as you can see, a task has many different jobs they do, and also that tasks should run indefinitely as long as the user somehow generates "jobs" for them. There should also be a way to enable/disable (start/pause) tasks. They say create the UI first so... I figure the best way to represent this is with a list-view widget, that lists all the tasks in the profile. Enabled tasks will be bold, disabled will be then when you double-click a task, a tab in the main view opens with all the settings, output, errors,. You can right click a task in the list-view to enable/disable/etc. So each task will be a closable tab, but when you close it just hides. My question is: should I extend from QAction and QTabWidget so I can easily drop tasks in and out of my list-view and tab bar? I'm thinking some way to make this plugin-based, since a lot of the plugins may share similar settings (like some of the same options, but different infos are input). Also, what's the best way to set up threading for this application?

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  • Behavior of virtual function in C++

    - by Summer_More_More_Tea
    Hi everyone: I have a question, here are two class below: class Base{ public: virtual void toString(); // generic implementation } class Derive : public Base{ public: ( virtual ) void toString(); // specific implementation } The question is: If I wanna subclass of class Derive perform polymophism using a pointer of type Base, is keyword virtual in the bracket necessary? If the answer is no, what's the difference between member function toString of class Derive with and without virtual?

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  • How to highlight ListView item on touch?

    - by AndroidNoob
    I have a simple ListView and I want each of it items to be highlighted on user's touch. I thought this should happen by default but it isn't. Can you advice? ListView xml: <ListView android:id="@+id/list_view" android:layout_width="fill_parent" android:layout_height="fill_parent" android:padding="10dp" android:divider="#206600" android:dividerHeight="2dp" android:smoothScrollbar="true" android:background="#ffffff" > </ListView> And code of my Adapter: private class MyAdapter extends ArrayAdapter<Task> { private LayoutInflater mInflater; public MyAdapter(Context context, int resource, List<Task> list) { super(context, resource, list); mInflater = LayoutInflater.from(context); } @Override public View getView(int position, View convertView, ViewGroup parent) { View v = convertView; if (v == null) { v = mInflater.inflate(R.layout.list_item, null); } Task task = taskList.get(position); /* Setup views from your layout using data in Object here */ return v; }

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  • How to avoid becoming a programmer while still beign closely involved with computer science/Industry

    - by WeShallOvercome
    I am studying computer science (A masters at an Ivy league), however most of the jobs i find involve way too much of programming. And frankly programming is not an issue, however programming without a meaning (read financial institution (non trading), other non mainstream jobs) bore me to death! I dont want to end up becoming a .NET,C#, Java kind of programmer. Can someone tell where i should look for jobs if i wish to do some real computer science work such as Machine Learning etc. I don't mind programming but becoming a Financial Software dev at Bloomeberg or an SDET at Microsoft isn't actually one of my goals. [note: I have interviewed for intern both positions listed above, and thankfully i got an intern for a data mining position in a top 750 Alexa rank web company] Sorry if angered anyone with a subjective question

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  • Whats wrong with the following code, its not compiling

    - by Ganesh Kundapur
    #include <iostream> #include <vector> using namespace std; class Base { public: void Display( void ) { cout<<"Base display"<<endl; } int Display( int a ) { cout<<"Base int display"<<endl; return 0; } }; class Derived : public Base { public: void Display( void ) { cout<<"Derived display"<<endl; } }; void main() { Derived obj; obj.Display(); obj.Display( 10 ); } $test1.cpp: In function ‘int main()’: test1.cpp:35: error: no matching function for call to ‘Derived::Display(int)’ test1.cpp:24: note: candidates are: void Derived::Display() On commenting obj.Display(10), it works.

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  • How do I execute queries upon DB connection in Rails?

    - by sycobuny
    I have certain initializing functions that I use to set up audit logging on the DB server side (ie, not rails) in PostgreSQL. At least one has to be issued (setting the current user) before inserting data into or updating any of the audited tables, or else the whole query will fail spectacularly. I can easily call these every time before running any save operation in the code, but DRY makes me think I should have the code repeated in as few places as possible, particularly since this diverges greatly from the ideal of database agnosticism. Currently I'm attempting to override ActiveRecord::Base.establish_connection in an initializer to set it up so that the queries are run as soon as I connect automatically, but it doesn't behave as I expect it to. Here is the code in the initializer: class ActiveRecord::Base # extend the class methods, not the instance methods class << self alias :old_establish_connection :establish_connection # hide the default def establish_connection(*args) ret = old_establish_connection(*args) # call the default # set up necessary session variables for audit logging # call these after calling default, to make sure conn is established 1st db = self.class.connection db.execute("SELECT SV.set('current_user', 'test@localhost')") db.execute("SELECT SV.set('audit_notes', NULL)") # end "empty variable" err ret # return the default's original value end end end puts "Loaded custom establish_connection into ActiveRecord::Base" sycobuny:~/rails$ ruby script/server = Booting WEBrick = Rails 2.3.5 application starting on http://0.0.0.0:3000 Loaded custom establish_connection into ActiveRecord::Base This doesn't give me any errors, and unfortunately I can't check what the method looks like internally (I was using ActiveRecord::Base.method(:establish_connection), but apparently that creates a new Method object each time it's called, which is seemingly worthless cause I can't check object_id for any worthwhile information and I also can't reverse the compilation). However, the code never seems to get called, because any attempt to run a save or an update on a database object fails as I predicted earlier. If this isn't a proper way to execute code immediately on connection to the database, then what is?

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  • make VIEW of SHOW TABLE query

    - by cneeds
    Is there a way to make a VIEW of this SHOW TABLE query? SHOW FULL TABLES FROM `db_name` WHERE `Table_type` = "Base table" When I save this as a view (using phpMyAdmin) I get #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SHOW FULL TABLES FROM `db_name` WHERE `Table_type` = "Base table"' at line 4 when phpMyAdmin tries to execute this CREATE ALGORITHM = UNDEFINED VIEW `Tables` AS SHOW FULL TABLES FROM `db_name` WHERE `Table_type` = "Base table"

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  • Inheritance - initialization problem

    - by dumbquestion
    I have a c++ class derived from a base class in a framework. The derived class doesn't have any data members because I need it to be freely convertible into a base class and back - the framework is responsible for loading and saving the objects and I can't change it. My derived class just has functions for accessing the data. But there are a couple of places where I need to store some temporary local variables to speed up access to data in the base class. mydata* MyClass::getData() { if ( !m_mydata ) { // set to NULL in the constructor m_mydata = some_long_and complex_operation_to_get_the_data_in_the_base() } return m_mydata; } The problem is if I just access the object by casting the base class pointer returned from the framework to MyClass* the ctor for MyClass is never called and m_mydata is junk. Is there a way of only initializing the m_mydata pointer once?

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  • Getting a type for a template instantiation?

    - by ebo
    I have the following situation: I have a object of type MyClass, which has a method to cast itself to it's base class. The class includes a typedef for it's base class and a method to do the downcast. template <class T, class B> class BaseClass; template <class T> class NoAccess; template <class T> class MyClass : public BaseClass<T, NoAccess<T> > { private: typedef BaseClass<T, NoAccess<T> > base; public: base &to_base(); }; I need to pass the result of a base call to a functor Operator: template <class Y> class Operator { Operator(Y &x); }; Operator<???> op(myobject.to_base()); Is there a easy way to fill the ??? provided that I do not want to use NoAccess?

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  • Figuring out what makes a C++ class abstract in VS2008

    - by suszterpatt
    I'm using VS2008 to build a plain old C++ program (not C++/CLI). I have an abstract base class and a non-abstract derived class, and building this: Base* obj; obj = new Derived(); fails with the error "'Derived': cannot instantiate abstract class". (It may be worth noting, however, that if I hover over Base with the cursor, VS will pop up a tooltip saying "class Base abstract", but hovering over Derived will only say "class Derived" (no "abstract")). The definitions of these classes are fairly large and I'd like to avoid manually checking if each method has been overridden. Can VS do this for me somehow? Any general tips on pinpointing the exact parts of the class' definition that make it abstract?

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  • Why doesn't C++ allow you to request a pointer to the most derived class?

    - by Matthew Lowe
    (This question should probably be answered with a reference to Stroustrup.) It seems extremely useful to be able to request a pointer to the most derived class, as in the following: class Base { ... }; class DerivedA { ... }; class DerivedB { ... }; class Processor { public: void Do(Base* b) {...} void Do(DerivedA* d) {...} void Do(DerivedB* d) {...} }; list<Base*> things; Processor p; for(list<Base*>::iterator i=things.begin(), e=things.end(); i!=e; ++i) { p.Do(CAST_TO_MOST_DERIVED_CLASS(*i)); } But this mechanism isn't provided in c++. Why?

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  • multiple models in Rails with a shared interface

    - by dfondente
    I'm not sure of the best structure for a particular situation in Rails. We have several types of workshops. The administration of the workshops is the same regardless of workshop type, so the data for the workshops is in a single model. We collect feedback from participants about the workshops, and the questionnaire is different for each type of workshop. I want to access the feedback about the workshop from the workshop model, but the class of the associated model will depend on the type of workshop. If I was doing this in something other than Rails, I would set up an abstract class for WorkshopFeedback, and then have subclasses for each type of workshop: WorkshopFeedbackOne, WorkshopFeedbackTwo, WorkshopFeedbackThree. I'm unsure how to best handle this with Rails. I currently have: class Workshop < ActiveRecord::Base has_many :workshop_feedbacks end class Feedback < ActiveRecord::Base belongs_to :workshop has_many :feedback_ones has_many :feedback_twos has_many :feedback_threes end class FeedbackOne < ActiveRecord::Base belongs_to :feedback end class FeedbackTwo < ActiveRecord::Base belongs_to :feedback end class FeedbackThree < ActiveRecord::Base belongs_to :feedback end This doesn't seem like to the cleanest way to access the feedback from the workshop model, as accessing the correct feedback will require logic investigating the Workshop type and then choosing, for instance, @workshop.feedback.feedback_one. Is there a better way to handle this situation? Would it be better to use a polymorphic association for feedback? Or maybe using a Module or Mixin for the shared Feedback interface? Note: I am avoiding using Single Table Inheritance here because the FeedbackOne, FeedbackTwo, FeedbackThree models do not share much common data, so I would end up with a large sparsely populated table with STI.

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  • Rails 3 HABTM Strange Association: Project and Employee in a tree.

    - by Mauricio
    Hi guys I have to adapt an existing model to a new relation. I have this: A Project has many Employees. the Employees of a Project are organized in some kind of hierarchy (nothing fancy, I resolved this adding a parent_id for each employee to build the 'tree') class Employee < AR:Base belongs_to :project belongs_to :parent, :class_name => 'Employee' has_many :childs, :class_name => 'Employee', :foreign_column => 'parent_id' end class Project < AR:Base has_many :employees, end That worked like a charm, now the new requirement is: The Employees can belong to many Projects at the same time, and the hierarchy will be different according to the project. So I though I will need a new table to build the HABTM, and a new class to access the parent_id to build the tree. Something like class ProjectEmployee < AR:Base belongs_to :project belongs_to :employee belongs_to :parent, :class_name => 'Employee' # <--- ?????? end class Project < AR:Base has_many :project_employee has_many :employees, :through => :project_employee end class Employee < AR:Base has_many :project_employee has_many :projects, :through => :project_employee end How can I access the parent and the childs of an employee for a given project? I need to add and remove childs as wish from the employees of a project. Thank you!

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  • How to implement a private virtual function within derived classes?

    - by Dane
    Hi, I know why I want to use private virtual functions, but how exactly can I implement them? For example: class Base{ [...] private: virtual void func() = 0; [...] } class Derived1: puplic Base{ void func() { //short implementation is ok here } } class Derived2: puplic Base{ void func(); //long implementation elsewhere (in cpp file) } [...] void Derived2::func() { //long implementation } The first version is ok but not always possible. Isn't the second version simply name hiding? How do you define the Base::func() of Derived2, if you cannot do it within the class declaration of Dereived2? Thanks

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  • Can I safely bind to data on multi-threaded applications?

    - by Paul
    Hi everyone, I'm trying to solve a classic problem - I have a multi-threaded application which runs some processor-intensive calculations, with a GUI interface. Every time one of the threads has completed a task, I'd like to update a status on a table taskID | status I use DataGridView and BindingList in the following way: BindingList<Task> tasks; dataGridView.DataSource = tasks public class Task : INotifyPropertyChanged { ID{get;} Status{get;set;} } Can a background thread safely update a task's status? and changes will be seen in the correct order in the GUI? Second Question: When do I need to call to PropertyChanged? I tried running with and without the call, didn't seem to bother.. Third Question: I've seen on MSDN that dataGridView uses BindingSource as a mediator between DataGridView.DataSource and BindingList Is this really necessary?

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  • Retrieve value of one column in a table

    - by user327094
    Here is my problem: I have 2 tables Accounts and Transaction Logs. in Accounts table, it has column "Amount" which is a base amount of an account. and in Trans Logs table, it also has column "Amount" which is additional (add or minus to the base amount) amount of the account. and I don't know how to retrieve that base amount to edit it, then save it back to the table. That means I need to get a value of the right column by using Acc_No to find. I'm using DataSet, by the way. i think it should go like this: Dim Amount as Decimal Amount = *the code to retrieve the base amount* Amount = Amount + txtAmount.Text *the code to save the new amount back to Accounts table* Thank you!

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  • How do I change the class of an object to a subclass of its current class in C++?

    - by Jared P
    I have an array of pointers to a base class, so that I can make those pointers point to (different) subclasses of the base class, but still interact with them. (really only a couple of methods which I made virtual and overloaded) I'm wondering if I can avoid using the pointers, and instead just make an array of the base class, but have some way to set the class to the subclass of my choosing. I know there must be something there specifying the class, as it needs to use that to look up the function pointer for virtual methods. By the way, the subclasses all have the same ivars and layout. Note: the design is actually based on using a template argument instead of a variable, due to performance increases, so really the abstract base class is just the interface for the subclasses, which are all the same except for their compiled code. Thanks

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  • how to avoid temporaries when copying weakly typed object

    - by Truncheon
    Hi. I'm writing a series classes that inherit from a base class using virtual. They are INT, FLOAT and STRING objects that I want to use in a scripting language. I'm trying to implement weak typing, but I don't want STRING objects to return copies of themselves when used in the following way (instead I would prefer to have a reference returned which can be used in copying): a = "hello "; b = "world"; c = a + b; I have written the following code as a mock example: #include <iostream> #include <string> #include <cstdio> #include <cstdlib> std::string dummy("<int object cannot return string reference>"); struct BaseImpl { virtual bool is_string() = 0; virtual int get_int() = 0; virtual std::string get_string_copy() = 0; virtual std::string const& get_string_ref() = 0; }; struct INT : BaseImpl { int value; INT(int i = 0) : value(i) { std::cout << "constructor called\n"; } INT(BaseImpl& that) : value(that.get_int()) { std::cout << "copy constructor called\n"; } bool is_string() { return false; } int get_int() { return value; } std::string get_string_copy() { char buf[33]; sprintf(buf, "%i", value); return buf; } std::string const& get_string_ref() { return dummy; } }; struct STRING : BaseImpl { std::string value; STRING(std::string s = "") : value(s) { std::cout << "constructor called\n"; } STRING(BaseImpl& that) { if (that.is_string()) value = that.get_string_ref(); else value = that.get_string_copy(); std::cout << "copy constructor called\n"; } bool is_string() { return true; } int get_int() { return atoi(value.c_str()); } std::string get_string_copy() { return value; } std::string const& get_string_ref() { return value; } }; struct Base { BaseImpl* impl; Base(BaseImpl* p = 0) : impl(p) {} ~Base() { delete impl; } }; int main() { Base b1(new INT(1)); Base b2(new STRING("Hello world")); Base b3(new INT(*b1.impl)); Base b4(new STRING(*b2.impl)); std::cout << "\n"; std::cout << b1.impl->get_int() << "\n"; std::cout << b2.impl->get_int() << "\n"; std::cout << b3.impl->get_int() << "\n"; std::cout << b4.impl->get_int() << "\n"; std::cout << "\n"; std::cout << b1.impl->get_string_ref() << "\n"; std::cout << b2.impl->get_string_ref() << "\n"; std::cout << b3.impl->get_string_ref() << "\n"; std::cout << b4.impl->get_string_ref() << "\n"; std::cout << "\n"; std::cout << b1.impl->get_string_copy() << "\n"; std::cout << b2.impl->get_string_copy() << "\n"; std::cout << b3.impl->get_string_copy() << "\n"; std::cout << b4.impl->get_string_copy() << "\n"; return 0; } It was necessary to add an if check in the STRING class to determine whether its safe to request a reference instead of a copy: Script code: a = "test"; b = a; c = 1; d = "" + c; /* not safe to request reference by standard */ C++ code: STRING(BaseImpl& that) { if (that.is_string()) value = that.get_string_ref(); else value = that.get_string_copy(); std::cout << "copy constructor called\n"; } If was hoping there's a way of moving that if check into compile time, rather than run time.

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  • Different button's name at the opening of jquery dialog

    - by Luca Belluco
    Hello, I have a dialog form and when I open it I have the button "add a task", I would like to keep this "name", when I open the form from an empty case, but I want to have a button named "edit this task" when I open an already existing task. I also want to send the form with this button when I push enter key, no matter where I am on the form. Thank you.

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  • patterns in case statement in bash scripting

    - by Ramiro Rela
    The man says that case statements use "filename expansion pattern matching". I usually want to have short names for some parameters, so I go: case $1 in req|reqs|requirements) TASK="Functional Requirements";; met|meet|meetings) TASK="Meetings with the client";; esac logTimeSpentIn "$TASK" I tried patterns like "req*" or "me{e,}t" which I understand would expand correctly to match those values in the context of filename expansion, but it doesn't work. Thanks.

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