# Ho to check for left button single click event vs click and drag event
**URL:** https://discourse.vtk.org/t/ho-to-check-for-left-button-single-click-event-vs-click-and-drag-event/3629
**Category:** Support
**Created:** [June 24, 2020, 5:39am UTC](https://discourse.vtk.org/t/ho-to-check-for-left-button-single-click-event-vs-click-and-drag-event/3629 "2020-06-24T05:39:34Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@dwventer](https://discourse.vtk.org/u/dwventer)
#### Post date: [June 24, 2020, 5:39am UTC](https://discourse.vtk.org/t/ho-to-check-for-left-button-single-click-event-vs-click-and-drag-event/3629/1 "2020-06-24T05:39:34Z")
I have a view with a vtkInteractorStyleTrackballCamera interactor. When you drag the mouse (left click and drag) it rotates the object. This is good. Now I want to return the mouse coordinates when the user does a single left button click and release.
At the moment, when I add a vtkCallbackCommand with the vtkCommand::KeyPressEvent the rotational ability of the object gets disabled. Any thoughts?
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [June 27, 2020, 9:11pm UTC](https://discourse.vtk.org/t/ho-to-check-for-left-button-single-click-event-vs-click-and-drag-event/3629/2 "2020-06-27T21:11:51Z")
Hi, Daniel,
Do you extend `vtkInteractorStyleTrackballCamera`? If so, you need to forward the event to the superclass: `vtkInteractorStyleTrackballCamera::OnLeftButtonDown();` in your class if you wish to maintain the original behavior in addition to the one of your code.
regards,
Paulo
---
### Author:  [@dwventer](https://discourse.vtk.org/u/dwventer)
#### Post date: [June 28, 2020, 11:09pm UTC](https://discourse.vtk.org/t/ho-to-check-for-left-button-single-click-event-vs-click-and-drag-event/3629/3 "2020-06-28T23:09:36Z")
Hi Paulo,
Thanks for your response. I have managed to find a solution to my problem. Not sure if it is the best one but it works.
I prefer to use observers then I do not have to do the whole inheritance thing. I added a callback method to my vtkInteractorStyleTrackballCamera object using the vtkCommand::LeftButtonPressEvent and the vtkCommand::LeftButtonReleaseEvent (on the same method).
I then record the mouse pointer location on the LeftButtonPressEvent and compare it to when the mouse button is released (LeftButtonReleaseEvent). If they match I then do my stuff. That is it.
Regards,
Daniel
---
### Author:  [@KaiHarvert](https://discourse.vtk.org/u/KaiHarvert)
#### Post date: [July 23, 2024, 8:05am UTC](https://discourse.vtk.org/t/ho-to-check-for-left-button-single-click-event-vs-click-and-drag-event/3629/4 "2024-07-23T08:05:30Z")
Hi, Paulo.I have a question. I Do not extend `vtkInteractorStyleTrackballCamera`,because I use C# program Kitware.VTK.When I drag the mouse (left click and drag) it rotates the object,but the event function: renWinInteractor.LeftButtonReleaseEvt+=LeftButtonReleaseEvt can not capture Button Release at once , As you say,in C++ program ,just need to forward the event to the superclass: `vtkInteractorStyleTrackballCamera::OnLeftButtonDown()`,I want to know how to realize this in Kitware.VTK using event function
regards
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [July 23, 2024, 7:20pm UTC](https://discourse.vtk.org/t/ho-to-check-for-left-button-single-click-event-vs-click-and-drag-event/3629/5 "2024-07-23T19:20:40Z")
Hello,
You first need to derive `vtkInteractorStyleTrackballCamera` to “forward the event to the superclass”. C# certainly has an inheritance mechanism.
best,
PC
---
### Author:  [@jaswantp](https://discourse.vtk.org/u/jaswantp)
#### Post date: [July 24, 2024, 7:52pm UTC](https://discourse.vtk.org/t/ho-to-check-for-left-button-single-click-event-vs-click-and-drag-event/3629/6 "2024-07-24T19:52:36Z")
Not sure about what’s available from Kitware’s C# VTK. If you’re doing it without extending the interactor style, it is best to listen to the interactor for events and then forward the event to the interactor style.
Here’s an example in C++, it should apply to Python and C# assuming VTK C# exposes the enums from `vtkCommand` and functions from interactor style.
```cpp
void OnLeftButtonDown(....)
{
// ...
// switch style could be a special case, so just to be safe, let's handle it.
auto* style = vtkInteractorStyle::SafeDownCast(interactor->GetInteractorStyle());
if (auto* switchableStyle = vtkInteractorStyleSwitch::SafeDownCast(style))
{
switchableStyle->GetCurrentStyle()->OnLeftButtonDown();
}
else
{
style->OnLeftButtonDown();
}
}
void OnLeftButtonUp(....)
{
// ...
// switch style could be a special case, so just to be safe, let's handle it.
auto* style = vtkInteractorStyle::SafeDownCast(interactor->GetInteractorStyle());
if (auto* switchableStyle = vtkInteractorStyleSwitch::SafeDownCast(style))
{
switchableStyle->GetCurrentStyle()->OnLeftButtonUp();
}
else
{
style->OnLeftButtonUp();
}
}
interactor->AddObserver(vtkCommand::LeftButtonPressEvent, OnLeftButtonDown);
interactor->AddObserver(vtkCommand::LeftButtonReleaseEvent, OnLeftButtonUp);
```
---
### Author:  [@Paulo\_Carvalho](https://discourse.vtk.org/u/Paulo_Carvalho)
#### Post date: [July 31, 2024, 6:53pm UTC](https://discourse.vtk.org/t/ho-to-check-for-left-button-single-click-event-vs-click-and-drag-event/3629/7 "2024-07-31T18:53:22Z")
Hello,
In case it’s not clear, C++, I do this:
```cpp
class MyInteractor : public vtkInteractorStyleTrackballCamera {
public:
...
void OnLeftButtonDown() override {
do_my_stuff();
// Forward the event to the base class to keep current behavior.
vtkInteractorStyleTrackballCamera::OnLeftButtonDown();
}
...
private:
...
protected:
...
};
```
I think translating this to C# is straightforward.
best,
PC