# Observer crash after double clicking

**URL:** https://discourse.vtk.org/t/observer-crash-after-double-clicking/11046
**Category:** Support
**Tags:** python
**Created:** [March 26, 2023, 7:53am UTC](https://discourse.vtk.org/t/observer-crash-after-double-clicking/11046 "2023-03-26T07:53:41Z")
**Posts on this page:** 2
**Page:** 1

<div class="post-metadata">

### Author: ![Hamedo\_Esk](https://discourse.vtk.org/user_avatar/discourse.vtk.org/hamedo_esk/32/6759_2.png) [@Hamedo\_Esk](https://discourse.vtk.org/u/Hamedo_Esk)
#### Post date: [March 26, 2023, 7:53am UTC](https://discourse.vtk.org/t/observer-crash-after-double-clicking/11046/1 "2023-03-26T07:53:41Z")

</div>

I made a simple app to track the number of clicks.  
Everything works fine and the number of clicks is printed as expected, but the observer stops working after performing double clicks.  
How can i solve this issue?

```auto
from PySide2 import QtWidgets
import pyvista as pv
import pyvistaqt
from vtkmodules.vtkInteractionStyle import vtkInteractorStyleTrackballCamera
import sys

class MainWindow(QtWidgets.QMainWindow):

    def __init__ (self, parent=None):
        super(MainWindow, self). __init__ (parent)

        self.frame = QtWidgets.QFrame()
        vlayout = QtWidgets.QVBoxLayout()
        self.vtk_widget = pyvistaqt.QtInteractor(self.frame)
        style = MyStyle()
        self.vtk_widget.interactor.SetInteractorStyle(style)
        vlayout.addWidget(self.vtk_widget)
        self.frame.setLayout(vlayout)
        self.setCentralWidget(self.frame)

        sphere = pv.Sphere()
        self.vtk_widget.add_mesh(sphere)

class MyStyle(vtkInteractorStyleTrackballCamera):
    def __init__ (self):
        super(). __init__ ()
        self.click_number = 0
        self.AddObserver("LeftButtonPressEvent", self.left_button_press_event)

    def left_button_press_event(self, obj, event):
        self.click_number += 1
        print(self.click_number)

if __name__ == " __main__":
    app = QtWidgets.QApplication(sys.argv)
    window = MainWindow()
    window.show()
    sys.exit(app.exec_())

```

---

<div class="post-metadata">

### Author: ![Hamedo\_Esk](https://discourse.vtk.org/user_avatar/discourse.vtk.org/hamedo_esk/32/6759_2.png) [@Hamedo\_Esk](https://discourse.vtk.org/u/Hamedo_Esk)
#### Post date: [March 27, 2023, 12:40pm UTC](https://discourse.vtk.org/t/observer-crash-after-double-clicking/11046/2 "2023-03-27T12:40:31Z")

</div>

I found the solution on my own.  
It’s better to add the observers directly to the `iren`:

```auto
from PySide2 import QtWidgets
import pyvista as pv
import pyvistaqt
import sys

class MyObserver:
    click_number = 0

    def clicker(self, obj, event):
        self.click_number += 1
        print(self.click_number)

class MainWindow(QtWidgets.QMainWindow):
    def __init__ (self, parent=None):
        super(MainWindow, self). __init__ (parent)

        self.frame = QtWidgets.QFrame()
        vlayout = QtWidgets.QVBoxLayout()
        self.vtk_widget = pyvistaqt.QtInteractor(self.frame)
        observer = MyObserver()
        # Add observer directly to the iren
        self.vtk_widget.iren.add_observer("LeftButtonPressEvent", observer.clicker)
        vlayout.addWidget(self.vtk_widget)
        self.frame.setLayout(vlayout)
        self.setCentralWidget(self.frame)

        sphere = pv.Sphere()
        self.vtk_widget.add_mesh(sphere)

if __name__ == " __main__":
    app = QtWidgets.QApplication(sys.argv)
    window = MainWindow()
    window.show()
    sys.exit(app.exec_())

```