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  • MVVM Binding To Property == Null

    - by LnDCobra
    I want to show some elements when a property is not null. What is the best way of achieving this? The following is my ViewModel: class ViewModel : ViewModelBase { public Trade Trade { get { return _trade; } set { SetField(ref _trade, value, () => Trade); } } private Trade _trade; } ViewModelBase inherits INotifyPropertyChanged and contains SetField() The Following is the Trade class: public class Trade : INotifyPropertyChaged { public virtual Company Company { get { return _company; } set { SetField(ref _company, value, () => Company); } } private Company _company; ...... } This is part of my View.xaml <GroupBox Visibility="{Binding Path=Trade.Company, Converter={StaticResource boolToVisConverter}}" /> I would like this groupbox to show only if Trade.Company is not null (so when a user selects a company). Would I need to create a custom converter to check for null and return the correct visibility or is there one in .NET?

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  • Syncronizing indices of function pointer table to table contents

    - by Thomas Matthews
    In the embedded system I'm working on, we are using a table of function pointers to support proprietary Dynamic Libraries. We have a header file that uses named constants (#define) for the function pointer indices. These values are used in calculating the location in the table of the function's address. Example: *(export_table.c)* // Assume each function in the table has an associated declaration typedef void (*Function_Ptr)(void); Function_Ptr Export_Function_Table[] = { 0, Print, Read, Write, Process, }; Here is the header file: *export_table.h* #define ID_PRINT_FUNCTION 1 #define ID_READ_FUNCTION 2 #define ID_WRITE_FUNCTION 3 #define ID_PROCESS_FUNCTION 4 I'm looking for a scheme to define the named constants in terms of their location in the array so that when the order of the functions changes, the constants will also change. (Also, I would like the compiler or preprocessor to calculate the indices to avoid human mistakes like typeo's.)

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  • Pointer to another classs as a property

    - by arjacsoh
    Why I receive an error when I try to create a property to another class through a pointer like that: #ifndef SQUARE_H #define SQUARE_H #include <string> //using namespace std; #include "Player.h" class Square { public: Square(int); void process(); protected: int ID; Player* PlayerOn; <--- }; #endif and the Player class is : #ifndef PLAYER_H #define PLAYER_H #include <string> //using namespace std; #include "Square.h" class Player { public: Player(int,int); // ~Player(void); int playDice(); private: int ID; int money; }; #endif I receive: syntax error missing ; before * (on the declaration of Player* PlayerOn;) and missing type specifier (on the same line...)

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  • Dynamic creation of a pointer function in c++

    - by Liberalkid
    I was working on my advanced calculus homework today and we're doing some iteration methods along the lines of newton's method to find solutions to things like x^2=2. It got me thinking that I could write a function that would take two function pointers, one to the function itself and one to the derivative and automate the process. This wouldn't be too challenging, then I started thinking could I have the user input a function and parse that input (yes I can do that). But can I then dynamically create a pointer to a one-variable function in c++. For instance if x^2+x, can I make a function double function(double x){ return x*x+x;} during run-time. Is this remotely feasible, or is it along the lines of self-modifying code?

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  • fetchedResultsController objectAtIndexPath: i "Passing argument 1 of objectAtIndexPath: makes pointer from integer without cast

    - by cocos2dbeginner
    NSMutableDictionary* dict = [[NSMutableDictionary alloc] init]; id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:0]; for (int i; i<[sectionInfo numberOfObjects]; i++) { NSManagedObject *o = [self.fetchedResultsController objectAtIndexPath:i]; [dict setObject:[[o valueForKey:@"frontCard"] description] forKey:@"frontCard"]; [dict setObject:[[o valueForKey:@"flipCard"] description] forKey:@"flipCard"]; } In this line NSManagedObject *o = [self.fetchedResultsController objectAtIndexPath:i]; i get this warning: warning: passing argument 1 of 'objectAtIndexPath:' makes pointer from integer without a cast

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  • Java - Does null variable require space in memory

    - by Yatendra Goel
    class CheckStore { private String displayText; private boolean state; private String meaningfulText; private URL url; public CheckStore(String text, boolean state) { this.displayText = text; this.state = state; } : : } As I am initializing only two variables (displayText and state) in the constructor, Will the rest two variables (meaningfulText and url which will have the value null) will require space in memory to store null value. Q1. I think they will require space. If they will, then how much memory does a null value takes in the memory (like int takes 4 bytes). Q2. How much space a string takes in memory. I guess it will depend on the length of the string. So how much space a string takes of how much length?

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  • Java Null Pointer Exception :-(

    - by John-Michael Reed
    I've got a Null Pointer Exception in my main that just won't go away and I'm totally out of ideas. The error is on the line "Board[x][y].color = 2;" in which Board is a public, static array of piece objects that contain instance variables like the one "color" that is being set to 2 in the above statement. Pieces is not static - that is there are many different copies of pieces, each with its own data, but only one board. The array has been initialized and defined as both public Piece[][] Board = new Piece[8][8] and public static Piece[][] Board = new Piece[8][8], but no matter how I mess around with it (getting rid of static, putting the variable in another object, etc.), I can't seem to get the error to go away. Help?

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  • MACRO Question: Returning pointer to a certain value

    - by Andrei Ciobanu
    Is it possible to write a MACRO that has a type and a value as its input parameters (MACRO(type,value)), and returns a valid pointer to a location that holds the submitted value. This macro should perform like the following function, but in a more generic manner: int *val_to_ptr(int val){ int *r = NULL; r = nm_malloc(sizeof(*r)); *r = val; return r; } Where nm_malloc() is a failsafe malloc. The Macro usage should be compatible with this usage: printf("%d",*MACRO(int,5)); Is it possible to achieve that ?

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  • if specific row = null, execute query

    - by fusion
    how do i check if the value of a column is null, and only then execute the query? for example: col1 col2 col3 01 abc i run a query which first checks if the record exists or not; if it exists, it should execute the update query and if it doesn't exist, it executes the insert query. how do i check if col3 is null and if it is null, it should execute the update query. . $sql = "SELECT uid FROM `users` WHERE uid = '" . $user_id . "'"; $result = mysql_query($sql,$conn) or die('Error:' .mysql_error()); $totalrows = mysql_num_rows($result); if($totalrows < 1) { insertUser($user_id,$sk, $conn); } else { updateSessionKey($user_id,$sk,$conn); }

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  • AutoComplete textbox and "Hide Pointer While Typing" in windows

    - by Joe
    How can the "Hide Pointer While Typing" option be disabled by application? I'm having an issue with the cursor hiding and not getting it back without pressing escape or losing window focus. The application has been written in C# and uses WPF. A technology specific answer is not required because it'll likely be possible using any technology. Here's the scenario: A user can type in a TextBox and an AutoComplete list shows up below the box. Once the user starts typing though, he/she can no longer select an item from the drop down because there is no mouse cursor. I noticed that Firefox does not have this behavior. For example, while typing in a URL in the address bar the mouse cursor never disappears. There are other places I've seen this behavior so I know it must be possible. Any help is greatly appreciated!

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  • How can I declare a pointer structure using {}?

    - by Y_Y
    This probably is one of the easiest question ever in C programming language... I have the following code: typedef struct node { int data; struct node * after; struct node * before; }node; struct node head = {10,&head,&head}; Is there a way I can make head to be *head [make it a pointer] and still have the availability to use '{ }' [{10,&head,&head}] to declare an instance of head and still leave it out in the global scope? For example: //not legal!!! struct node *head = {10,&head,&head};

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  • SQL Select between two fields depending on the value of one field

    - by Filip
    Hi. I am using a PostgreSQL database, and in a table representing some measurements I've two columns: measurement, and interpolated. In the first I've the observation (measurement), and b is the interpolated value depending on nearby values. Every record with an original value has also an interpolated value. However, there are a lot of records without "original" observations (NULL), hence the values are interpolated and stored in the second column. So basically there are just two cases in the database: Value Value NULL Value Of course, it is preferable to use the value from the first column if available, hence I need to build a query to select the data from the first column, and if not available (NULL), then the database returns the value from the second column for the record in question. I have no idea how to build the SQL query. Please help. Thanks.

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  • C pointer question, dereferencing crash

    - by skynorth
    Why do this work? int *var; while(scanf("%d", &var) && *var != 0) printf("%d \n", var); While this does not? int *var; while(scanf("%d", &var) && var != 0) printf("%d \n", var); Doesn't * (dereference operator) give you the value pointed by the pointer? So why does *var != 0 crash the program, while var != 0 does not?

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  • Handling null values with PowerShell dates

    - by Tim Ferrill
    I'm working on a module to pull data from Oracle into a PowerShell data table, so I can automate some analysis and perform various actions based on the results. Everything seems to be working, and I'm casting columns into specific types based on the column type in Oracle. The problem I'm having has to do with null dates. I can't seem to find a good way to capture that a date column in Oracle has a null value. Is there any way to cast a [datetime] as null or empty?

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  • Create JavaScript array of function pointer, without calling it

    - by sibidiba
    I have the code below. I would like to have an array (buttons) with a single element pointing to the a function (closeFlag). <script type="text/javascript"> var closeFlag = new function() { alert('Clicked'); } var buttons = { 'OK': closeFlag } </script> However, when loading the page the alert immediately pops up. When the array is constructed, instead of using it as a pointer, JavaScript calls my function. Why? What mistake, misconception do I have?

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  • Activiti Engine: Task Event - User is null

    - by sockeqwe
    I have a problem, which should be simple to solve, but i can't find the method to call to solve this problem: My problem is, that every Task Event (org.activiti.engine.task.Event) returnes null by calling Event.getUserId(); If I take a look into the database I see that the database table ACT_HI_COMMENT has null as value for the column USER_ID_ for every row. I generate these TaskEvents programmatically by calling (for example) processEngine.getTaskService().addComment(task.getId(), null, commentMessage); processEngine.getTaskService().addUserIdentityLink(task.getId(), user.getId(), IDENTITY_LINK_OBSERVER); I guess there is a simple method that I must call to solve this problem, something like processEngine.setCurrentUser(authenticatedUser.getId()); Any suggestions?

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  • GWT : NULL Session

    - by jidma
    I'm using spring4gwt in my project. I have the following login service implementation: @Service("loginService") public class LoginServiceImpl extends RemoteServiceServlet implements LoginService { @Override @Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class) public UserBean checkUser(String userName, String password) throws Exception { HttpSession httpSession = getThreadLocalRequest().getSession(); } } When i call the loginService.checkUser("test","test") (In hosted mode), I get a null pointer exception, as getThreadLocalRequest() returns NULL instead of the actual session. I didn't try in web mode yet. Why would I get a null session ? Does it have something to do with spring4gwt ? Thank you

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  • How to set the pointer to the current row in the Datagridview in C#

    - by user286546
    I have a datagridview on the Windows Form in c#. I am updating and filling the table adapter on the cell event. The problem is that When I go to lower half of the datagrid which is not visible until I scroll down, as I click any cell, the table adapter is filled and updated and the pointerpoints to the very first row. Any suggestion on how to fix it. I have a ideas to record the top row of the datagridview that is visible and set the pointer to that row. But how to do it?

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  • C++ - Creating folder method

    - by Matthew
    I have the following method in C++: void create_folder(LPCWSTR full_folder) //Method to create folder in case it does not exist { if(!CreateDirectory(full_folder,attr)) //Checking whether the folder already exists { switch (GetLastError()) { case ERROR_ALREADY_EXISTS: printf("The folder already exists!\n\n"); break; case NULL: printf("The folder does not exist!\n\n"); printf("The folder was created successfully!\n\n"); break; } } } In case the folder already exists, the correct message is displayed on the screen. However, if the folder does NOT exist, nothing is displayed on the screen, that is, the part identified by case NULL is not executed. How can I solve this problem? In other words, how can I get the code after the case NULL to run if the folder does not exist?

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  • AS3: Performance question calling an event function with null param

    - by adehaas
    Lately I needed to call a listener function without an actual listener like so: foo(null); private function foo(event:Event):void { //do something } So I was wondering if there is a significant difference regarding performance between this and using the following, in which I can prevent the null in calling the function without the listener, but am still able to call it with a listener as well: foo(); private function foo(event:Event = null):void { } I am not sure wether it is just a question of style, or actually bad practice and I should write two similar functions, one with and one without the event param (which seems cumbersome to me). Looking forward to your opinions, thx.

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  • passing a float as a pointer to a matrix

    - by numerical25
    Honestly, I couldnt think of a better title for this issue because I am having 2 problems and I don't know the cause. The first problem I have is this //global declaration float g_posX = 0.0f; ............. //if keydown happens g_posX += 0.03f; &m_mtxView._41 = g_posX; I get this error cannot convert from 'float' to 'float *' So I assume that the matrix only accepts pointers. So i change the varible to this.... //global declaration float *g_posX = 0.0f; ............. //if keydown happens g_posX += 0.03f; &m_mtxView._41 = &g_posX; and I get this error cannot convert from 'float' to 'float *' which is pretty much saying that I can not declare g_posX as a pointer. honestly, I don't know what to do.

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  • Misunderstanding function pointer - passing it as an argument

    - by Stef
    I want to pass a member function of class A to class B via a function pointer as argument. Please advise whether this road is leading somewhere and help me fill the pothole. #include <iostream> using namespace std; class A{ public: int dosomeA(int x){ cout<< "doing some A to "<<x <<endl; return(0); } }; class B{ public: B(int (*ptr)(int)){ptr(0);}; }; int main() { A a; int (*APtr)(int)=&A::dosomeA; B b(APtr); return 0; } This brilliant piece of code leaves me with the compiler error: cannot convert int (A::*)(int)' toint (*)(int)' in initialization Firstly I want it to compile. Secondly I don't want dosomeA to be STATIC.

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  • char pointer array in c#

    - by james
    consider the following c++ code #include "stdafx.h" #include<iostream> using namespace std; void ping(int,char* d[]); void ping(int a,char *b[]) { int size; size=sizeof(b)/sizeof(int); // total size of array/size of array data type //cout<<size; for(int i=0;i<=size;i++) cout<<"ping "<<a<<b[i]<<endl; } int _tmain(int argc, _TCHAR* argv[]) { void (*funcptr)(int,char* d[]); char* c[]={"a","b"}; funcptr= ping; funcptr(10,c); return 0; } how can i implement the same in c#.. m new to c#. how can i have char pointer array in c#?

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  • this pointer to base class constructor?

    - by Rolle
    I want to implement a derived class that should also implement an interface, that have a function that the base class can call. The following gives a warning as it is not safe to pass a this pointer to the base class constructor: struct IInterface { void FuncToCall() = 0; }; struct Base { Base(IInterface* inter) { m_inter = inter; } void SomeFunc() { inter->FuncToCall(); } IInterface* m_inter; }; struct Derived : Base, IInterface { Derived() : Base(this) {} FuncToCall() {} }; What is the best way around this? I need to supply the interface as an argument to the base constructor, as it is not always the dervied class that is the interface; sometimes it may be a totally different class. I could add a function to the base class, SetInterface(IInterface* inter), but I would like to avoid that.

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  • Pointer aliasing- in C++0x

    - by DeadMG
    I'm thinking about (just as an idea) disjointed pointer aliasing in C++0x. I was thinking about seeing if it could be implemented similarly to const correctness- that is, enforced by the compiler. What would be the requirements for such a thing? As this is more of a thought experiment, I'm perfectly happy to look at solutions that destroy legacy code or redefine half the language and that kind of thing. What I'd really rather not do is have, say, restrict from C99 where the programmer just promises it. It should be enforced.

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