App crash on emitting signal

[TagLog]

Hi everyone,

In my app I emit a signal when a variable in TaskGraphicsScene (QGraphicsScene custom class) is changed:

//TaskGraphicsScene.cpp
void TaskGraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *btnReleased){
  if(btnReleased->button() == Qt::LeftButton){
      //view as current node
      *currentPointer = taskShown;
      emit changeTask();
  }
}

When the signal is recieved by the MainWindow class, the app crashes.

I have seen this post but I don't know how to "so i moved signals into the graphics item class and added a getter function to the graphics view which returns a pointer to that graphics item. now, main widget will get signals directly from the graphics item." as the OP did.

Any tip or clue?? Thank you.

[KonradMD]

Hi, can you post your connection

[TagLog]

This is my connection, I have 12 TaskGraphicsScenes in the UI:

    for(unsigned i= 0; i < 12; i++){
      connect(childrenScenes[i], SIGNAL(changeTask()), this, SLOT(on_taskChanged()));
    }

[jsulm]

@TagLog said in App crash on emitting signal:

on_taskChanged

What does on_taskChange do? Did you try to use debugger to go step by step through it to see where exactly it crashes and why?

[Pradeep Kumar]

Hi,

check the return status of connect statement.
and check logs in slot() and function where ur emmitting signal();

Thanks,

[dheerendra]

on_taskChanged() slot must be culprit here. You can focus on the code inside the slot. You can use debugger to look at the issue as @jslum already suggested.

[TagLog]

@jsulm It call another function called updateWindow(), but that function is also called by other buttons and stuff, so the problem is in the connection/signal/slot

[SGaist]

Hi,

Please post the stack trace of your crash, that should help pinpoint the problem.

[TagLog]

@SGaist

This is the stack trace (as a newbie, I think the problem could be in thread 1, the last one in the stack trace), in a breakpoint the debugger says this message: Disassembler failed: Cannot access memory at address 0x6a85097c, the function is unknown (??)

[jsulm]

@TagLog
Can you show the content of following methods:

• MainWindow::updateTree
• MainWindow::updateWindow
• MainWindow::on_taskChanged
  ?

[TagLog]

@jsulm
Here you go:

void MainWindow::on_taskChanged(){
  updateWindow();
}

void MainWindow::updateWindow()
{

  currentScene->clear();

  for (unsigned i = 0; i < 12; i ++){
      childrenScenes[i]->clear();
  }

  ui->btnModify->setEnabled(true);
  ui->btnComplete->setEnabled(true);
  ui->btnAddChild->setEnabled(true);

  ui->lblProjectTitle->setText(currentProj.getTitle());
  ui->lblCurrentTitle->setText(currentTask->getTitle());
  ui->tedCurrentText->setText(currentTask->getText());

  currentTask->drawAsCurrent(currentScene);

  for(unsigned i = 0; i < 12 && i < currentTask->getChildren().size(); i++){
      childrenScenes[i]->setTaskShown(currentTask->getChildren()[i] );
      childrenScenes[i]->drawTaskShown();
  }
  updateTree();
}

void MainWindow::updateTree(){

  QString TaskTree;
  Task* masterPointer = currentTask;

  while(masterPointer != Q_NULLPTR){
      TaskTree = "/" + masterPointer->getTitle() + TaskTree;
      masterPointer = currentTask->getMaster();
  }

  ui->lblDepTree->setText(TaskTree);
}

I'm willing for any explanation if you need

[BjornW]

First suspects are the following:

 for (unsigned i = 0; i < 12; i ++){
      childrenScenes[i]->clear();
  }

and

  for(unsigned i = 0; i < 12 && i < currentTask->getChildren().size(); i++){
      childrenScenes[i]->setTaskShown(currentTask->getChildren()[i] );
      childrenScenes[i]->drawTaskShown();
  }

Are you confident thay you remain in bounds here? for both containers (currentTask->getChildren() and childrenScenes)?

EDIT: also, what is

currentTask

? Is it set properly?

[VRonin]

If you make assumptions in your code, assert them (even static assert them if you can)

• is currentTask null?
• is currentScene null?
• is childrenScenes of size >=12
• is any childrenScenes[i] null

The easiest way to debug this is put a breakpoint at the first line of on_taskChanged and step into/over every line untill you find exactly where it explodes and fix whatever is wrong there

[TagLog]

@BjornW In this test case I remain in bounds in those lines of code.

currentTask is a pointer to a custom class object which is initialized at the beginnning of the test.

[VRonin]

@VRonin said in App crash on emitting signal:

The easiest way to debug this is put a breakpoint at the first line of on_taskChanged and step into/over every line untill you find exactly where it explodes and fix whatever is wrong there

[TagLog]

@VRonin I'm doing this right now, as soon as I finish I'll tell you what I found

Edit: I can't find anything now, but for few days I can't look at the code, I'll continue to look ASAP

[TagLog]

@VRonin

I finally found what caused crashes: it was the UpdateTree function. I wrote a wrong line which caused an infinite loop. I'm feeling both stupid and happy :) / :(