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• Dynamic Object Not Creating for Privately Inherited Class.

  - by mahesh

  Hi, What is the reason for the following code that does not let me to create object. class base { public: void foo() { cout << "base::foo()"; } }; class derived : private base { public: void foo() { cout << "deived::foo()"; } }; void main() { base *d = new derived(); d->foo(); } It Gives me error : " 'type cast' : conversion from 'derived *' to 'base *' exists, but is inaccessible" Thanks in advance :)

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• How do I find out if an object can be Invoke()'d?

  - by Jurily

  Consider the following class: public class Event<T> { public delegate void Handler<t>(t msg); private event Handler<T> E; public void connect(Delegate handler) { E += delegate(T msg) { object target = handler.Target; if (Invokable(target) { target.BeginInvoke(handler, new object[] { msg }); } }; } public void emit(T msg) { if ( E != null ) { E(msg); } } private static bool Invokable(object o) { // magic } } How do I implement Invokable(), and what else do I need for this code to compile?

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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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• Java Swing- Create a function to add elements to JScrollPanel

  - by battousai622

  I want to create a function so that i can call add JLabel's, etc inside the JScrollPanel. I am not sure what the command is in NetBeans. I tried doing JScrollPanel - events - container - componentAdded to create the code below. But nothing shows up when i add code to that function. private void initComponents() { scrollPanel = new javax.swing.JScrollPane(); scrollPanel.addContainerListener(new java.awt.event.ContainerAdapter() { public void componentAdded(java.awt.event.ContainerEvent evt) { scrollPanelComponentAdded(evt); } } private void scrollPanelComponentAdded(java.awt.event.ContainerEvent evt) { System.out.println("main"); } Any help would be great, thanks.

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• How can I delete video stored in the photo library ?

  - by srikanth rongali

  I have saved video in to the photo library. -(void)exportVideo:(id)sender { NSString *path = [DOCUMENTS_FOLDER stringByAppendingString:@"/air.mp4"]; NSLog(@"Path:%@", path); NSLog(@"Export Button CLicked"); UISaveVideoAtPathToSavedPhotosAlbum(path, self, @selector(video:didFinishSavingWithError: contextInfo:), nil); } - (void)video:(NSString *)videoPath didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo { NSLog(@"Finished saving video with error: %@", error); } Now I need to delete the video i have stored programmatically. How can I delete the video ? Are there any functions for it? Thank You.

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• Please see following code and answer

  - by user323422

  template <class T> class _cExplicitInstation { public: void show1(T c) { double d =10.02 ; std::cout<<c; } void show2(T d) { std::cout<<d; } }; template _cExplicitInstation<char>; template void _cExplicitInstation<int>::show1(int c); int main() { _cExplicitInstation<char> abc; _cExplicitInstation<int>().show2(10);// it should show error as i have // explicitly declare for show1() function but its working // can u tell why? }

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• How does C++ free the memory when a constructor throws an exception and a custom new is used

  - by Joshua

  I see the following constructs: new X will free the memory if X constructor throws. operator new() can be overloaded. The canonical definition of an operator new overload is void *operator new(heap h) and the corrisponding operator delete. The most common operator new overload is pacement new, which is void *operator new(void *p) { return p; } You almost always cannot call delete on the pointer given to placement new. This leads to a single question. How is memory cleaned up when X constructor throws and an overloaded new is used?

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• XAML-based applications - Event Naming Conventions for C#

  - by user118190

  For event handling, I am starting to see many coders doing this: XButton.Click += OnXButtonClicked() ... void OnXButtonClicked() { ... } Where did this On_ convention come from? It just doesn't feel right in terms of methods. I am starting to see this as well and am wondering what others thought: XButton.Click += HandleXButtonClick() ... void HandleXButtonClick() { ... } When using intellisense, Visual Studio handles these like so: XButton.Click += XButton_Click; ... void XButton_Click(object sender, RoutedEventArgs e) { ... } I am seeking some advice on these naming conventions and would greatly appreciate some advice.

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• Java SWING- Create a function to add elements to JScrollPanel ??? PLEASE

  - by battousai622

  I want to create a function so that i can call add JLables, ect inside the JScrollPanel. Im not sure what the command is in netbeans. I tried doing JScrollPanel - events - container - componentAdded to create the code below. But nothing shows up when i add code to that function. Any help would be great please! =] private void initComponents() { scrollPanel = new javax.swing.JScrollPane(); scrollPanel.addContainerListener(new java.awt.event.ContainerAdapter() { public void componentAdded(java.awt.event.ContainerEvent evt) { scrollPanelComponentAdded(evt); } } private void scrollPanelComponentAdded(java.awt.event.ContainerEvent evt) { System.out.println("main"); }

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• Android: Prompt user to save changes when Back button is pressed

  - by chriskopec

  I have an activity that contains several user editable items (an EditText field, RatingBar, etc). I'd like to prompt the user if the back/home button is pressed and changes have been made that have not yet been saved. After reading through the android documentation, it seems like this piece of code should go in the onPause method. I've tried putting an AlertDialog in the onPause however the dialog gets shown and then immediately tears down because nothing is there to block the pause from completing. This is what I've come up with so far: @Override protected void onPause() { super.onPause(); AlertDialog ad = new AlertDialog.Builder(this).setMessage( R.string.rating_exit_message).setTitle( R.string.rating_exit_title).setCancelable(false) .setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { // User selects OK, save changes to db } }).setNeutralButton(android.R.string.cancel, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { // User selects Cancel, discard all changes } }).show(); } Am I on the right track or is there another way to accomplish what I'm trying to do here? Any help would be great!

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• How to Execute Base Class's Method Before Implementors's Method?

  - by DaveDev

  I have the following page public partial class GenericOfflineCommentary : OfflineFactsheetBase { } where OfflineFactsheetBase is defined as public class OfflineFactsheetBase : System.Web.UI.Page { public OfflineFactsheetBase() { this.Load += new EventHandler(this.Page_Load); this.PreInit += new EventHandler(this.Page_PreInit); } protected void Page_PreInit(object sender, EventArgs e) { if (Request.QueryString["data"] != null) { this.PageData = StringCompressor.DecompressString(Request.QueryString["data"]); this.ExtractPageData(); } } } OfflineFactsheetBase has the following virtual method: public virtual void ExtractPageData() { // get stuff relevant to all pages that impmement OfflineFactsheetBase } which is implemented in all pages that impmement OfflineFactsheetBase as follows: public partial class GenericOfflineCommentary : OfflineFactsheetBase { public override void ExtractPageData() { // get stuff relevant to an OfflineCommentary page. } } Currently, only GenericOfflineCommentary's ExtractPageData() is firing. How can I modify this to first run OfflineFactsheetBase's ExtractPageData() and then GenericOfflineCommentary's? edit: I'm trying to avoid having to call base.ExtractPageData() in every implementor. Is this possible?

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• doubt in Exceptions

  - by Ajay Singh

  class MyException extends Exception { MyException() {} MyException(String msg) { super(msg);} } public class NewException { static void f() throws MyException { System.out.println("throwing exception from f()"); throw new ClassCastException(); } static void g() throws MyException { System.out.println("throwing exception from g()"); throw new MyException("parametrized "); } public static void main(String ...strings ) { try { f(); } catch(MyException e) { e.printStackTrace(System.out); } try { g(); } catch(MyException e) { e.printStackTrace(System.out); } } } In the function f() iam specifying that "MyException " exception will be thrown and actually iam throwing some other exception which has no relation with MyException but still the compiler does not report any complain.Why is it so??

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• C++: namespace conflicht between extern "C" and class member

  - by plaisthos

  Hi, I stumbled upon a rather exotic c++ namespace problem: condensed example: extern "C" { void solve(lprec * lp); } class A { public: lprec * lp; void solve(int foo); } void A::solve(int foo) { solve(lp); } I want to call the c funcition solve in my C++ member function A::solve. The compiler is not happy with my intents: error C2664: 'lp_solve_ilp::solve' : cannot convert parameter 1 from 'lprec *' to 'int' Is there something I can prefix the solve function? C::solve does not work

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• ASP.NET null reference exception

  - by nanek

  Please help me to figure out what is wrong with this code: I have ASP.NET page with one button visible. When user clicks it - it instances MyClass (its implementation is in AppCode directory) and turns invisible (button2 becomes visible). When I click button2 it raises "Object reference not set to an instance of an object" Exception. What seems to be the problem? { public MyClass noviTest; protected void Page_Load(object sender, EventArgs e) { } protected void Button1_Click(object sender, EventArgs e) { noviTest = new MyClass(TextBox1.Text); Button1.Visible = false; Button2.Visible = true; } protected void Button2_Click(object sender, EventArgs e) { Label1.Text=noviTest.getID; //this is the critical line } } Thank You in advance, Regards

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• PropertyGrid + interface

  - by nilphilus

  public interface ITest { void Somethink(); } public class Test1 : ITest { public void Somethink() { /* do stuff */ } public int Test1Property { get; set; } } public class Test2 : ITest { public void Somethink() { /* do stuff */ } public float Test2Property { get; set; } } //Main class public class MainClass { [TypeConverter(ExpandableObjectConverter)] public ITest test { get; set; } } Ok, i have sth like this. Instance of MainClass is selected by PropertyGrid. How to make a DropDownList of objects of classes which implement ITest (here Test1 and Test2)

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• How to obtain listview information without refreshing the page?

  - by user1808098

  I am currently developing an Android Application for my Final Year Project. But to be honest I do not have any basic knowledges and everything started from scratch and referring to online tutorials a lot. Here is my question, I was trying to retrieve data from listview activity. There are two listview in my page using button. I was able to display the first listview but when it get data for the second listview, the data for first listview is disappeared because the page is refreshed, vice versa. What code should I modified to get both the data in the page? (Database not implemented yet) Please help, thanks a lot. Below are my codings. Codings for XML. <!-- Location --> <TextView android:id="@+id/TextViewLocation" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:layout_marginBottom="10dip" android:text="Location Information" android:gravity="center" android:textSize="15dip" android:textColor="#025f7c"/> <!-- Condition Label --> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:textColor="#372c24" android:text="Traffic Condition"/> <Button android:id="@+id/inputListView" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:layout_marginBottom="10dip" android:text="choose one..."/> <!-- Comment Label --> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:textColor="#372c24" android:text="What's Happening?"/> <Button android:id="@+id/inputListView2" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:layout_marginBottom="10dip" android:text="choose one..."/> <!-- Suggestion Label --> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:textColor="#372c24" android:text="Comments / Suggestion"/> <EditText android:layout_width="fill_parent" android:layout_height="80dp" android:layout_marginTop="5dip" android:layout_marginBottom="10dip" android:singleLine="true"/> <!-- Image button --> <Button android:id="@+id/btnImage" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:text="Upload Image"/> <!-- Report button --> <Button android:id="@+id/btnReportCheckin" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:text="Report"/> <!-- Link to Logout --> <TextView android:id="@+id/linkLogout" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_marginTop="5dip" android:layout_marginBottom="40dip" android:text="Log Out" android:gravity="center" android:textSize="20dip" android:textColor="#025f7c"/> </LinearLayout> <!-- Check or Report Form Ends --> Codings for Activity Class public class CheckinActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Set View to checkin.xml setContentView(R.layout.checkin); /* TextView LocationView = (TextView) findViewById(R.id.TextViewLocation); Intent h = getIntent(); // getting attached intent data String address = h.getStringExtra("address"); // displaying selected product name LocationView.setText(address); */ Button ListViewScreen = (Button) findViewById(R.id.inputListView); //Listening to Button ListViewScreen.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //Switching to ListView Screen Intent i = new Intent(getApplicationContext(), ListViewActivity.class); startActivity(i); } } ); Button SelectedView = (Button) findViewById(R.id.inputListView); Intent i = getIntent(); // getting attached intent data String product = i.getStringExtra("product"); // displaying selected product name SelectedView.setText(product); Button ListView2Screen = (Button) findViewById(R.id.inputListView2); //Listening to Button ListView2Screen.setOnClickListener(new View.OnClickListener() { public void onClick(View v) { //Switching to ListView Screen Intent j = new Intent(getApplicationContext(), ListView2Activity.class); startActivity(j); } } ); Button SelectedView2 = (Button) findViewById(R.id.inputListView2); Intent j = getIntent(); // getting attached intent data String product2 = j.getStringExtra("product2"); // displaying selected product name SelectedView2.setText(product2); TextView Logout = (TextView) findViewById(R.id.linkLogout); // Listening to Log out Logout.setOnClickListener(new View.OnClickListener() { public void onClick(View arg0) { // Closing menu screen // Switching to Login Screen/closing register screen finish(); } }); } } Coding for listview class public class ListViewActivity extends ListActivity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // storing string resources into Array String[] traffic_condition = getResources().getStringArray(R.array.traffic_condition); // Binding resources Array to ListAdapter this.setListAdapter(new ArrayAdapter<String>(this, R.layout.listitem, R.id.listViewLayout, traffic_condition)); ListView lv = getListView(); // listening to single list item on click lv.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View view, int position, long id) { // selected item String product = ((TextView) view).getText().toString(); // Launching new Activity on selecting single List Item Intent i = new Intent(getApplicationContext(), CheckinActivity.class); // sending data to new activity i.putExtra("product", product); startActivity(i); } }); } } Hope I made myself clear, I can provide a screen shot of my apps if it is required, thanks!

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• g++ doesn't think I'm passing a reference

  - by Ben Jones

  When I call a method that takes a reference, g++ complains that I'm not passing a reference. I thought that the caller didn't have to do anything different for PBR. Here's the offending code: //method definition void addVertexInfo(VertexInfo &vi){vertexInstances.push_back(vi);} //method call: sharedVertices[index]->addVertexInfo(VertexInfo(n1index, n2index)); And here's the error: GLUtils/GLMesh.cpp: In member function 'void GLMesh::addPoly(GLIndexedPoly&)': GLUtils/GLMesh.cpp:110: error: no matching function for call to 'SharedVertexInfo::addVertexInfo(VertexInfo)' GLUtils/GLMesh.h:93: note: candidates are: void SharedVertexInfo::addVertexInfo(VertexInfo&)

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• Mvp View knows Model

  - by userbb

  I'm trying to use MVP and I notice that my View must know Model that should not happen in MVP I presume. here is example: public partial class TestForm : Form, ITestPresenter { public void LoadList(IEnumerable<AppSignature> data) { testPresenterBindingSource.DataSource = data; } } public interface ITestPresenter { event EventHandler<EventArgs> Load; void LoadList(IEnumerable<AppSignature> data); } and the problem is that in TestForm I need reference to AppSignature. In all tutorials I saw, there are some simple examples like public void LoadList(IEnumerable<String> data) where there is no need reference to model. But how i.e DataGridView can publish current row data?

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• Why baseclass calls method of subclass?

  - by twlkyao

  I encounter some code like the following: BaseClass: public class BaseClass { String name = "Base"; public BaseClass() { printName(); } public void printName() { System.out.println(name + "——Base"); } } DrivedClass: public class SubClass extends BaseClass { String name = "Sub"; public SubClass() { printName(); } public void printName() { System.out.println(name + "——Sub"); } public static void main(String[] args) { new SubClass(); } } When run the code, the output is: null——Sub Sub——Sub while it should be: Base——Base Sub——Sub I wonder why the BaseClass constructor calls the SubClass method, can anybody explain this? Thanks in advance.

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• How to Execute Base Class's ExtractPageData() Before Implementors's ExtractPageData()?

  - by DaveDev

  I have the following page public partial class GenericOfflineCommentary : OfflineFactsheetBase { } where OfflineFactsheetBase is defined as public class OfflineFactsheetBase : System.Web.UI.Page { public OfflineFactsheetBase() { this.Load += new EventHandler(this.Page_Load); this.PreInit += new EventHandler(this.Page_PreInit); } protected void Page_PreInit(object sender, EventArgs e) { if (Request.QueryString["data"] != null) { this.PageData = StringCompressor.DecompressString(Request.QueryString["data"]); this.ExtractPageData(); } } } OfflineFactsheetBase has the following virtual method: public virtual void ExtractPageData() { // get stuff relevant to all pages that impmement OfflineFactsheetBase } which is implemented in all pages that impmement OfflineFactsheetBase as follows: public partial class GenericOfflineCommentary : OfflineFactsheetBase { public override void ExtractPageData() { // get stuff relevant to an OfflineCommentary page. } } Currently, only GenericOfflineCommentary's ExtractPageData() is firing. How can I modify this to first run OfflineFactsheetBase's ExtractPageData() and then GenericOfflineCommentary's?

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• Partial coverage of a return statement in C++/CLI

  - by brickner

  I have C++/CLI code and I'm using Visual Studio 2008 Team Suite Code Coverage. The code header: // Library.h #pragma once #include <string> using namespace System; namespace Library { public ref class MyClass { public: static void MyFoo(); static std::string Foo(); }; } The code implementation: #include "Library.h" using namespace Library; using namespace System; void MyClass::MyFoo() { Foo(); } std::string MyClass::Foo() { return std::string(); } I have a C# unit test, that calls MyClass.MyFoo(): [TestMethod] public void TestMethod1() { Library.MyClass.MyFoo(); } For some reason, I don't get a full code coverage for MyClass. The Foo() method has 3 uncovered blocks and 5 covered blocks. The closing curly brackets (}) are marked in orange - partially covered. I have no idea why is it partially covered instead of fully covered, and this is my question.

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• Java Timer not working

  - by Jacob

  I have an Image named worldImageToUse and I have a Timer that is supposed to toggle worldImageToUse between two images every 1 second. But it does not seem to work. Help Please? public void startWorldImageFlash() { worldImageFlashTimer = new Timer(); TimerTask task = new TimerTask() { @Override public void run() { if(worldImageToUse == worldImage) setWorldImageBW(); if(worldImageToUse == worldImageBW) setWorldImageColor(); } }; worldImageFlashTimer.scheduleAtFixedRate(task, 0, 1000); } public void stopWorldImageFlash() { worldImageFlashTimer.cancel(); setWorldImageColor(); }

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• How I change a variable of a type to another one in C?

  - by drigoSkalWalker

  I want to do it: int main () { bla bla bla void *onetype; switch (USER_INPUT_TYPE) { CASE CONVERT_TO_CHAR: convert onetype VOID TO CHAR >>> HOW??? CASE CONVERT_TO_INT: convert onetype VOID TO INT >>> HOW??? LOT OF CASES... } } Yes, I know type casting, but type casting is a 'temporary' change. So, is there any way to accomplish it in C? EDIT : Stop stop stop! Please, see, what are you doing is type casting, I KNOW THIS, you are creating another variable of the desirable type like int i = (int) onetype, I don't want this, I want something else like onetype = (int) onetype, without recreate them, without allocate another variable. Thanks a lot guys!

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• Why would you precede the main() function in C with a data type?

  - by Milktrader

  Many are familiar with the hello world program in C #include <stdio.h> main () { printf ("hello world"); return 0; } Why do some precede the main () function with int as in: int main() Also, I've seen the word 'void' entered inside the () as in: int main(void) It seems like extra typing for nothing, but maybe it's a best practice that pays dividends in other situations? Also, why precede main() with an int if you're returning a character string? If anything, one would expect: char main(void) I'm also foggy about why we return 0 at the end of the function.

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• Google App Engine datastore-primary key

  - by megala

  Hi, I've created a table in the Google App Engine Datastore. It contains the following FIELDS(GROUPNAME,GROUPID,GROUPDESC). How do I set GROUPID as the primary key? My code is as follows: @Entity @Table(name="group" , schema="PUBLIC") public class Creategroup { @Basic private String groupname; @Basic private String groupid; @Basic private String groupdesc; public void setGroupname(String groupname) { this.groupname = groupname; } public String getGroupname() { return groupname; } public void setGroupid(String groupid) { this.groupid = groupid; } public String getGroupid() { return groupid; } public void setGroupdesc(String groupdesc) { this.groupdesc = groupdesc; } public String getGroupdesc() { return groupdesc; } public Creategroup(String groupname, String groupid, String groupdesc ) { // TODO Auto-generated constructor stub this.groupname = groupname; this.groupid = groupid; this.groupdesc = groupdesc; } }

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