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Slot is being called multiple times every time a signal is emitted

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margin-bottom:0;

17

4

I am using one signal and slot connection in a block. My code as follows

in a.cpp

 QObject::connect(m_ptheFlange2Details,SIGNAL(GetFlang1DimAfterAnalysis()),
 this,SLOT(GetFlang1DimAftrAnalysis()));

 m_ptheFlange2Details->get();// one function inside which i am emiting
 // GetFlang1DimAfterAnalysis() signal ;

 QObject::disconnect(m_ptheFlange2Details,SIGNAL(GetFlang1DimAfterAnalysis()),
 this,SLOT(GetFlang1DimAftrAnalysis()));

Inside the get() function when this emit statement executes, the slot is called lots of times. Where as according to me it should call only once.

c++ qt qt4

share|improve this question

edited Oct 1 '15 at 17:07

Rick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

asked Jun 11 '12 at 6:20

KentaKenta

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• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  Have you make sure that connect is not called multiple times??!!! Please show us a little bit more code. In which function connect and disconnect has been written??
  
  – Ammar
  Jun 11 '12 at 6:24
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  How many times is emit called in get()?
  
  – cmannett85
  Jun 11 '12 at 6:31
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  This code looks good.Now post the ugly part of your code!
  
  – ScarCode
  Jun 11 '12 at 9:35
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Check if QObject::disconnect(...) returns true. If it does, then this part of the code is OK. You may have trouble in get(), or elsewhere.
  
  – Kuba Ober
  Jun 11 '12 at 16:10
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  i am using only one emit statement inside get() , then how can this slot invoke for lots of time ??QObject::disconnect(--) also returns true . i am not able to understand whats the problem ... shall i go for QObject::uniqueconnection()
  
  – Kenta
  Jun 12 '12 at 11:39
  
  

  
  
  
  

add a comment
 | 

17

4

I am using one signal and slot connection in a block. My code as follows

in a.cpp

 QObject::connect(m_ptheFlange2Details,SIGNAL(GetFlang1DimAfterAnalysis()),
 this,SLOT(GetFlang1DimAftrAnalysis()));

 m_ptheFlange2Details->get();// one function inside which i am emiting
 // GetFlang1DimAfterAnalysis() signal ;

 QObject::disconnect(m_ptheFlange2Details,SIGNAL(GetFlang1DimAfterAnalysis()),
 this,SLOT(GetFlang1DimAftrAnalysis()));

Inside the get() function when this emit statement executes, the slot is called lots of times. Where as according to me it should call only once.

c++ qt qt4

share|improve this question

edited Oct 1 '15 at 17:07

Rick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

asked Jun 11 '12 at 6:20

KentaKenta

1,20444 gold badges2424 silver badges5050 bronze badges

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  Have you make sure that connect is not called multiple times??!!! Please show us a little bit more code. In which function connect and disconnect has been written??
  
  – Ammar
  Jun 11 '12 at 6:24
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  How many times is emit called in get()?
  
  – cmannett85
  Jun 11 '12 at 6:31
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  This code looks good.Now post the ugly part of your code!
  
  – ScarCode
  Jun 11 '12 at 9:35
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Check if QObject::disconnect(...) returns true. If it does, then this part of the code is OK. You may have trouble in get(), or elsewhere.
  
  – Kuba Ober
  Jun 11 '12 at 16:10
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  i am using only one emit statement inside get() , then how can this slot invoke for lots of time ??QObject::disconnect(--) also returns true . i am not able to understand whats the problem ... shall i go for QObject::uniqueconnection()
  
  – Kenta
  Jun 12 '12 at 11:39
  
  

  
  
  
  

add a comment
 | 

I am using one signal and slot connection in a block. My code as follows

in a.cpp

 QObject::connect(m_ptheFlange2Details,SIGNAL(GetFlang1DimAfterAnalysis()),
 this,SLOT(GetFlang1DimAftrAnalysis()));

 m_ptheFlange2Details->get();// one function inside which i am emiting
 // GetFlang1DimAfterAnalysis() signal ;

 QObject::disconnect(m_ptheFlange2Details,SIGNAL(GetFlang1DimAfterAnalysis()),
 this,SLOT(GetFlang1DimAftrAnalysis()));

Inside the get() function when this emit statement executes, the slot is called lots of times. Where as according to me it should call only once.

c++ qt qt4

share|improve this question

edited Oct 1 '15 at 17:07

Rick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

asked Jun 11 '12 at 6:20

KentaKenta

1,20444 gold badges2424 silver badges5050 bronze badges

 QObject::connect(m_ptheFlange2Details,SIGNAL(GetFlang1DimAfterAnalysis()),
 this,SLOT(GetFlang1DimAftrAnalysis()));

 m_ptheFlange2Details->get();// one function inside which i am emiting
 // GetFlang1DimAfterAnalysis() signal ;

 QObject::disconnect(m_ptheFlange2Details,SIGNAL(GetFlang1DimAfterAnalysis()),
 this,SLOT(GetFlang1DimAftrAnalysis()));

share|improve this question

edited Oct 1 '15 at 17:07

Rick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

asked Jun 11 '12 at 6:20

KentaKenta

1,20444 gold badges2424 silver badges5050 bronze badges

share|improve this question

edited Oct 1 '15 at 17:07

Rick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

asked Jun 11 '12 at 6:20

KentaKenta

1,20444 gold badges2424 silver badges5050 bronze badges

edited Oct 1 '15 at 17:07

Rick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

edited Oct 1 '15 at 17:07

Rick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

asked Jun 11 '12 at 6:20

KentaKenta

1,20444 gold badges2424 silver badges5050 bronze badges

asked Jun 11 '12 at 6:20

KentaKenta

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1 Answer
1

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32

As stated in some of the comments, this is usually caused by calling the connect more the once. The slot will be called once for every time the connection is made. For example, the following code will result in slot() being called 3 times when signal() is emitted once.

connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));

If you are doing connects in code that may be run more than once, it is generally a good idea to use Qt::UniqueConnection as the 5th parameter. The following code will result in slot() being called 1 time when signal() is emitted once.

connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);

I'm guessing the reason your code is not working correctly is because you are omitting the 5th parameter and connect defaults to Qt::DirectConnection (for single threaded programs). This immediately calls the slot as if it were a function call. This means that it is possible for connect to be called again before the disconnect happens (if there are loops in your program).

share|improve this answer

edited Aug 27 '13 at 18:32

answered Jun 12 '12 at 17:48

Rick SmithRick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  if you are emitting a signal , then only the slot is being called right ?? it does not matter how many times you have used the connect statement .. could you please describe something on Qt::uniqueconnection ..since i am new to qt , so dont have more idea on it ..
  
  – Kenta
  Jun 14 '12 at 7:29
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It does matter how many times you call connect unless you use Qt::UniqueConnection. If you are doing connects in a function, and you call that function more than once, you need to use Qt::UniqueConnection or your slot will get called multiple times. I edited my post to try to show that a little better.
  
  – Rick Smith
  Jun 14 '12 at 21:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Rick--Thankxxx
  
  – Kenta
  Jun 15 '12 at 5:11
  

  
  
  
  

add a comment
 | 

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32

As stated in some of the comments, this is usually caused by calling the connect more the once. The slot will be called once for every time the connection is made. For example, the following code will result in slot() being called 3 times when signal() is emitted once.

connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));

If you are doing connects in code that may be run more than once, it is generally a good idea to use Qt::UniqueConnection as the 5th parameter. The following code will result in slot() being called 1 time when signal() is emitted once.

connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);

I'm guessing the reason your code is not working correctly is because you are omitting the 5th parameter and connect defaults to Qt::DirectConnection (for single threaded programs). This immediately calls the slot as if it were a function call. This means that it is possible for connect to be called again before the disconnect happens (if there are loops in your program).

share|improve this answer

edited Aug 27 '13 at 18:32

answered Jun 12 '12 at 17:48

Rick SmithRick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  if you are emitting a signal , then only the slot is being called right ?? it does not matter how many times you have used the connect statement .. could you please describe something on Qt::uniqueconnection ..since i am new to qt , so dont have more idea on it ..
  
  – Kenta
  Jun 14 '12 at 7:29
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It does matter how many times you call connect unless you use Qt::UniqueConnection. If you are doing connects in a function, and you call that function more than once, you need to use Qt::UniqueConnection or your slot will get called multiple times. I edited my post to try to show that a little better.
  
  – Rick Smith
  Jun 14 '12 at 21:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Rick--Thankxxx
  
  – Kenta
  Jun 15 '12 at 5:11
  

  
  
  
  

add a comment
 | 

32

As stated in some of the comments, this is usually caused by calling the connect more the once. The slot will be called once for every time the connection is made. For example, the following code will result in slot() being called 3 times when signal() is emitted once.

connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));

If you are doing connects in code that may be run more than once, it is generally a good idea to use Qt::UniqueConnection as the 5th parameter. The following code will result in slot() being called 1 time when signal() is emitted once.

connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);

I'm guessing the reason your code is not working correctly is because you are omitting the 5th parameter and connect defaults to Qt::DirectConnection (for single threaded programs). This immediately calls the slot as if it were a function call. This means that it is possible for connect to be called again before the disconnect happens (if there are loops in your program).

share|improve this answer

edited Aug 27 '13 at 18:32

answered Jun 12 '12 at 17:48

Rick SmithRick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  if you are emitting a signal , then only the slot is being called right ?? it does not matter how many times you have used the connect statement .. could you please describe something on Qt::uniqueconnection ..since i am new to qt , so dont have more idea on it ..
  
  – Kenta
  Jun 14 '12 at 7:29
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It does matter how many times you call connect unless you use Qt::UniqueConnection. If you are doing connects in a function, and you call that function more than once, you need to use Qt::UniqueConnection or your slot will get called multiple times. I edited my post to try to show that a little better.
  
  – Rick Smith
  Jun 14 '12 at 21:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Rick--Thankxxx
  
  – Kenta
  Jun 15 '12 at 5:11
  

  
  
  
  

add a comment
 | 

As stated in some of the comments, this is usually caused by calling the connect more the once. The slot will be called once for every time the connection is made. For example, the following code will result in slot() being called 3 times when signal() is emitted once.

connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));

If you are doing connects in code that may be run more than once, it is generally a good idea to use Qt::UniqueConnection as the 5th parameter. The following code will result in slot() being called 1 time when signal() is emitted once.

connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);

I'm guessing the reason your code is not working correctly is because you are omitting the 5th parameter and connect defaults to Qt::DirectConnection (for single threaded programs). This immediately calls the slot as if it were a function call. This means that it is possible for connect to be called again before the disconnect happens (if there are loops in your program).

share|improve this answer

edited Aug 27 '13 at 18:32

answered Jun 12 '12 at 17:48

Rick SmithRick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()));

connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);
connect(obj, SIGNAL(signal()), obj2, SLOT(slot()), Qt::UniqueConnection);

share|improve this answer

edited Aug 27 '13 at 18:32

answered Jun 12 '12 at 17:48

Rick SmithRick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

answered Jun 12 '12 at 17:48

Rick SmithRick Smith

6,99199 gold badges6161 silver badges7575 bronze badges

answered Jun 12 '12 at 17:48

Rick SmithRick Smith

6,99199 gold badges6161 silver badges7575 bronze badges