[vtkusers] When to delete objects?

[Godofredo]

Well, again many many thanks. I followed Mike's suggestion and used
vtkSmartPointer for my local objects. It worked ok for all local objects but
for the last filter I use in the local function. I explain the code flow so
you can make an idea: 
I have a function that takes a point cloud stored in a PolyData as input and
extracts a set of points which are inside a predefined volume. The output of
this function is also a PolyData. The flow is: define 2 implicit spheres
(vtkSphere) -> calculate the volume difference (vtkImplicitBoolean)
->extract the points inside the calculated volume
(vtkExtractPolyDataGeometry)->clean the data (vtkCleanPolyData) -> store the
output of vtkCleanPolyData in a Polydata which the function returns. Next to
this I call another function which triangulates the extracted points. 
The problem is that I can  wrap all objects using vtkSmartPointer except the
last filter (i.e. vtkCleanPolyData). If I wrap that one the execution of the
code crashes when calling the delaunay filter in the next function. Any
ideas?  



Mike Jackson-9 wrote:
> 
> Also you can use the vtkSmartPointer class to wrap your local  
> objects, so taking some of the examples from below:
> 
> void myfunction()
> {
>    vtkSmartPointer<vtkSomething> something =  
> vtkSmartPointer<vtkSomething>::New(); //ref count starts as 1
>    //do some things here
>   // 'something' will be deleted when this method returns, saving a  
> line of code and ensuring that the object is cleaned up.
> }
> 
> 
> Just my two cents..
> -- 
> Mike Jackson   Senior Research Engineer
> Innovative Management & Technology Services
> 
> 
> On May 21, 2007, at 9:40 AM, David E DeMarle wrote:
> 
>> Hello,
>>
>> This is what I do:
>> 1)  Make sure there is a Delete() for each New() around each  
>> temporary (local) use.
>>
>> void myfunction()
>> {
>>   vtkSomething *something = vtkSomething::New(); //ref count starts  
>> as 1
>>   //do some things here
>>   something->Delete(); //ref count -- = 0 which will call  
>> something's destructor to and deallocate it
>> }
>>
>> 2) When I want to keep the object around and use it later, I save  
>> it in an ivar within a class, and destroy it in the classes  
>> destructor, or whenever the instance of the object is replaced with  
>> another one.
>>
>> class MyClass {
>>   MyClass()
>>   {
>>     this->MySomething = NULL;
>>   }
>>   ~MyClass()
>>   {
>>     if (this->MySomething != NULL)
>>       {
>>       this->MySomething->Delete();
>>       }
>>   }
>>
>>   void MyFunction()
>>   {
>>    if (this->MySomething != NULL) //Delete what I might have made  
>> before
>>    {
>>       this->MySomething->Delete();
>>    }
>>    this->MySomething = vtkSomething::New();//Create a new thing it  
>> starts with ref count 1
>>
>>    //now you can use it and not call Delete(), because the  
>> destructor will eventually
>>    for (int i = 0; i < 99; i++)
>>    {
>>       this->MySomething->CallAMethod();
>>       ...
>>       this->UseIt();
>>       ...
>>    }
>>   }
>>
>>   void UseIt()
>>   {
>>     if (this->MySomething) //sanity check
>>     {
>>       this->MySomething->DoSomething();
>>     }
>>   }
>> }
>>
>> 3) If I need to pass a reference to another object I register it.
>> MyClass::PassItOff(AnotherClass *other)
>> {
>>    if (this->MySomething)
>>    {
>>       other->HisCopy == this->MySomething();
>>       this->MySomething->Register(); //ref count goes to 2, so now  
>> it will only be freed when this, and other Delete() it to make ref  
>> count 0
>>    }
>> }
>>
>> Note:
>> For subclasses of vtkObject you don't have to go through the steps  
>> of checking the old pointer, saving the new pointer and  
>> incrementing the reference count manually, you can just use the  
>> vtkSetObject Macro in VTK/Common/vtkSetGet.h
>> So
>>
>> Also note: to test if you've got it right, turn on the  
>> VTK_DEBUG_LEAKS flag in cmake. When on, the program will check for  
>> any vtkObjects that have not been Delete()'d thoroughly as it ends  
>> and print them.
>>
>> hth,
>> Dave DeMarle
>>
>>
>>
>> On 5/21/07, burlen <burlen at apollo.sr.unh.edu> wrote:
>> Hi,
>> Here is what I do,
>>
>> 1) when ever you ::New() something you also Delete() it.
>>
>> 2a) When ever you need to keep the output of a filter longer than  
>> the filter itself call Register(0) on the output then Delete() the  
>> filter. Make sure you Delete() the output later.
>>
>> 2b) alternatively you could DeepCopy the output of filters you want  
>> to keep around.
>>
>> Burlen
>>
>>
>> Godofredo wrote:
>>> Hi everyone. I'm trying to make the triangulation of a point cloud  
>>> using
>>> vtkDelaunay2D. What I don't know is when to exactly delete filters  
>>> and other
>>> objects such as PolyDatas that aren't used anymore. I've made some  
>>> tries but
>>>
>>> with bad results. For example, if I use vtkDelaunay2D, update it  
>>> and then
>>> save its output in a vtkPolyData, can I delete the vtkDelaunay2D  
>>> filter?
>>> Many thanks.
>>>
>>
>> -- 
>>
>>
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>>
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> 
> 
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