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Please help with lambda sytax

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  • A Offline
    A Offline
    Anonymous_Banned275
    wrote on last edited by
    #15

    Please note - I am posting this to illustrate the problem, please please please - NO comments on my programming style!

    My primary goal is to duplicate XML "connect" using code.
    The attached code and its variations generally compiles - that is one goal done.

    HOWEVER - it crashes during run time and I SUSPECT the problem is
    after
    clicking button 11 my code builds new instance of scanner dialog and it has build-in timers . The "list" is , in theory, filed AFTER each item individual timer expire.
    BUT
    my test connect is executed immediately after the first timer expires and the "item" is changed .

    I am asking - is it possible I have a timing problem?

    Here is my current - under construction connect to copy the "list" lines.
    All it does - just compiles and cannot be tested , in existing code , due to this issue.

    #ifdef BYPASS
        // interacts with pushing buitto 11
        // keeps crashing
        
        connect(
                    this->ui->list,
                    //          SIGNAL(ui->list->currentTextChanged()),
                    SIGNAL(ui->list->itemDoubleClicked(*pItem)),
                    //           SIGNAL(DDD->ui->list->itemChanged(TEST_LABEL)),
                    //           SIGNAL(itemClicked(QListWidgetItem *)),
                    //              SIGNAL(itemChanged(TEST_LABEL)),
                    this->ui->plainTextEdit,
                    //           SLOT(DDD->ui->plainTextEdit->appendPlainText(TEST_LABEL))
                    //             SLOT(appendPlainText(TEST_LABEL))
                    SLOT(ui->plainTextEdit->appendPlainText(*pItem)));
        //           );
        
    #endif
        
        
    

    This is how it tracks when working - without the code above

    QDEBUG TRACE 
    QDEBUG TRACE TASK 
    		 END imoplement Device DiscoiveryDialog  
    
    QDEBUG TRACE TASK 
    		 find nearby BT devices 
    
    file      /media/f/QT/QT_PROJECT/TEST_PROJECT_14/mainwindow_cat_tab.cpp
    function  on_pushButton_11_clicked
    @line     236
    TEMPORARY EXIT 
    /home/f/build-TEST_PROJECT-Desktop-Debug/TEST_PROJECT exited with code 0
    

    And this is failing track

    QDEBUG TRACE 
    QDEBUG TRACE TASK 
    		 START imoplement Device DiscoveryDialog  
    
    QDEBUG TRACE TASK 
    		 find nearby BT devices 
    
    file      /media/f/QT/QT_PROJECT/TEST_PROJECT_14/mainwindow_cat_tab.cpp
    function  on_pushButton_11_clicked
    @line     206
    TEMPORARY EXIT 
    TRACE SCAN FLOW 
    			 START TOK TRACE SCAN FLOW CONSTRUCTOR 
    			DeviceDiscoveryDialog::DeviceDiscoveryDialog(QWidget *parent)
    
    
    TEMPORARY exit  @line 
    133
    The program has unexpectedly finished.
    /home/f/build-TEST_PROJECT-Desktop-Debug/TEST_PROJECT crashed
    

    Again - all I am asking - is it possible I have a timing problem?

    jsulmJ JonBJ 3 Replies Last reply
    0
    • A Anonymous_Banned275

      Please note - I am posting this to illustrate the problem, please please please - NO comments on my programming style!

      My primary goal is to duplicate XML "connect" using code.
      The attached code and its variations generally compiles - that is one goal done.

      HOWEVER - it crashes during run time and I SUSPECT the problem is
      after
      clicking button 11 my code builds new instance of scanner dialog and it has build-in timers . The "list" is , in theory, filed AFTER each item individual timer expire.
      BUT
      my test connect is executed immediately after the first timer expires and the "item" is changed .

      I am asking - is it possible I have a timing problem?

      Here is my current - under construction connect to copy the "list" lines.
      All it does - just compiles and cannot be tested , in existing code , due to this issue.

      #ifdef BYPASS
          // interacts with pushing buitto 11
          // keeps crashing
          
          connect(
                      this->ui->list,
                      //          SIGNAL(ui->list->currentTextChanged()),
                      SIGNAL(ui->list->itemDoubleClicked(*pItem)),
                      //           SIGNAL(DDD->ui->list->itemChanged(TEST_LABEL)),
                      //           SIGNAL(itemClicked(QListWidgetItem *)),
                      //              SIGNAL(itemChanged(TEST_LABEL)),
                      this->ui->plainTextEdit,
                      //           SLOT(DDD->ui->plainTextEdit->appendPlainText(TEST_LABEL))
                      //             SLOT(appendPlainText(TEST_LABEL))
                      SLOT(ui->plainTextEdit->appendPlainText(*pItem)));
          //           );
          
      #endif
          
          
      

      This is how it tracks when working - without the code above

      QDEBUG TRACE 
      QDEBUG TRACE TASK 
      		 END imoplement Device DiscoiveryDialog  
      
      QDEBUG TRACE TASK 
      		 find nearby BT devices 
      
      file      /media/f/QT/QT_PROJECT/TEST_PROJECT_14/mainwindow_cat_tab.cpp
      function  on_pushButton_11_clicked
      @line     236
      TEMPORARY EXIT 
      /home/f/build-TEST_PROJECT-Desktop-Debug/TEST_PROJECT exited with code 0
      

      And this is failing track

      QDEBUG TRACE 
      QDEBUG TRACE TASK 
      		 START imoplement Device DiscoveryDialog  
      
      QDEBUG TRACE TASK 
      		 find nearby BT devices 
      
      file      /media/f/QT/QT_PROJECT/TEST_PROJECT_14/mainwindow_cat_tab.cpp
      function  on_pushButton_11_clicked
      @line     206
      TEMPORARY EXIT 
      TRACE SCAN FLOW 
      			 START TOK TRACE SCAN FLOW CONSTRUCTOR 
      			DeviceDiscoveryDialog::DeviceDiscoveryDialog(QWidget *parent)
      
      
      TEMPORARY exit  @line 
      133
      The program has unexpectedly finished.
      /home/f/build-TEST_PROJECT-Desktop-Debug/TEST_PROJECT crashed
      

      Again - all I am asking - is it possible I have a timing problem?

      jsulmJ Offline
      jsulmJ Offline
      jsulm
      Lifetime Qt Champion
      wrote on last edited by jsulm
      #16

      @AnneRanch said in Please help with lambda sytax:

      connect(
      this->ui->list,
      // SIGNAL(ui->list->currentTextChanged()),
      SIGNAL(ui->list->itemDoubleClicked(*pItem)),
      // SIGNAL(DDD->ui->list->itemChanged(TEST_LABEL)),
      // SIGNAL(itemClicked(QListWidgetItem *)),
      // SIGNAL(itemChanged(TEST_LABEL)),
      this->ui->plainTextEdit,
      // SLOT(DDD->ui->plainTextEdit->appendPlainText(TEST_LABEL))
      // SLOT(appendPlainText(TEST_LABEL))
      SLOT(ui->plainTextEdit->appendPlainText(*pItem)));
      // );

      This is invalid connect() call. Please check https://doc.qt.io/qt-5/signalsandslots.html And it is better to use Qt5 connect() syntax to detect such issues during compile time instead of run time.
      It should be

      connect(
          this->ui->list,
          SIGNAL(itemDoubleClicked(QListWidgetItem*)),
          this->ui->plainTextEdit,
          SLOT(appendPlainText(QListWidgetItem*)));
      

      But this will also not work as QPlainTextEdit does not have a slot appendPlainText which takes a QListWidgetItem* as parameter (use new Qt5 connect syntax and a lambda)...

      https://forum.qt.io/topic/113070/qt-code-of-conduct

      A 1 Reply Last reply
      5
      • A Anonymous_Banned275

        Please note - I am posting this to illustrate the problem, please please please - NO comments on my programming style!

        My primary goal is to duplicate XML "connect" using code.
        The attached code and its variations generally compiles - that is one goal done.

        HOWEVER - it crashes during run time and I SUSPECT the problem is
        after
        clicking button 11 my code builds new instance of scanner dialog and it has build-in timers . The "list" is , in theory, filed AFTER each item individual timer expire.
        BUT
        my test connect is executed immediately after the first timer expires and the "item" is changed .

        I am asking - is it possible I have a timing problem?

        Here is my current - under construction connect to copy the "list" lines.
        All it does - just compiles and cannot be tested , in existing code , due to this issue.

        #ifdef BYPASS
            // interacts with pushing buitto 11
            // keeps crashing
            
            connect(
                        this->ui->list,
                        //          SIGNAL(ui->list->currentTextChanged()),
                        SIGNAL(ui->list->itemDoubleClicked(*pItem)),
                        //           SIGNAL(DDD->ui->list->itemChanged(TEST_LABEL)),
                        //           SIGNAL(itemClicked(QListWidgetItem *)),
                        //              SIGNAL(itemChanged(TEST_LABEL)),
                        this->ui->plainTextEdit,
                        //           SLOT(DDD->ui->plainTextEdit->appendPlainText(TEST_LABEL))
                        //             SLOT(appendPlainText(TEST_LABEL))
                        SLOT(ui->plainTextEdit->appendPlainText(*pItem)));
            //           );
            
        #endif
            
            
        

        This is how it tracks when working - without the code above

        QDEBUG TRACE 
        QDEBUG TRACE TASK 
        		 END imoplement Device DiscoiveryDialog  
        
        QDEBUG TRACE TASK 
        		 find nearby BT devices 
        
        file      /media/f/QT/QT_PROJECT/TEST_PROJECT_14/mainwindow_cat_tab.cpp
        function  on_pushButton_11_clicked
        @line     236
        TEMPORARY EXIT 
        /home/f/build-TEST_PROJECT-Desktop-Debug/TEST_PROJECT exited with code 0
        

        And this is failing track

        QDEBUG TRACE 
        QDEBUG TRACE TASK 
        		 START imoplement Device DiscoveryDialog  
        
        QDEBUG TRACE TASK 
        		 find nearby BT devices 
        
        file      /media/f/QT/QT_PROJECT/TEST_PROJECT_14/mainwindow_cat_tab.cpp
        function  on_pushButton_11_clicked
        @line     206
        TEMPORARY EXIT 
        TRACE SCAN FLOW 
        			 START TOK TRACE SCAN FLOW CONSTRUCTOR 
        			DeviceDiscoveryDialog::DeviceDiscoveryDialog(QWidget *parent)
        
        
        TEMPORARY exit  @line 
        133
        The program has unexpectedly finished.
        /home/f/build-TEST_PROJECT-Desktop-Debug/TEST_PROJECT crashed
        

        Again - all I am asking - is it possible I have a timing problem?

        JonBJ Offline
        JonBJ Offline
        JonB
        wrote on last edited by JonB
        #17

        @AnneRanch
        As @jsulm has said. As long as you use the old-style SIGNAL & SLOT() macros, you are liable to have code which compiles OK but does not behave correctly at runtime. With the new style syntax, if the signal/slot code is wrong, you get told at compile-time. It might seem harder to get it right, but at least you know that when it does compile it will do what you expect when you run it; if it does not compile, you have to sort it out to be correct at that stage.

        1 Reply Last reply
        0
        • jsulmJ jsulm

          @AnneRanch said in Please help with lambda sytax:

          connect(
          this->ui->list,
          // SIGNAL(ui->list->currentTextChanged()),
          SIGNAL(ui->list->itemDoubleClicked(*pItem)),
          // SIGNAL(DDD->ui->list->itemChanged(TEST_LABEL)),
          // SIGNAL(itemClicked(QListWidgetItem *)),
          // SIGNAL(itemChanged(TEST_LABEL)),
          this->ui->plainTextEdit,
          // SLOT(DDD->ui->plainTextEdit->appendPlainText(TEST_LABEL))
          // SLOT(appendPlainText(TEST_LABEL))
          SLOT(ui->plainTextEdit->appendPlainText(*pItem)));
          // );

          This is invalid connect() call. Please check https://doc.qt.io/qt-5/signalsandslots.html And it is better to use Qt5 connect() syntax to detect such issues during compile time instead of run time.
          It should be

          connect(
              this->ui->list,
              SIGNAL(itemDoubleClicked(QListWidgetItem*)),
              this->ui->plainTextEdit,
              SLOT(appendPlainText(QListWidgetItem*)));
          

          But this will also not work as QPlainTextEdit does not have a slot appendPlainText which takes a QListWidgetItem* as parameter (use new Qt5 connect syntax and a lambda)...

          A Offline
          A Offline
          Anonymous_Banned275
          wrote on last edited by
          #18

          @jsulm said in Please help with lambda sytax:

          But this will also not work as QPlainTextEdit does not have a slot appendPlainText which takes a QListWidgetItem* as parameter (use new Qt5 connect syntax and a lambda)...

          I do appreciate the post.
          It may seems strange, but at this point I am NOT after "it" working.
          I just need to figure out WHY adding this "connect" , in any form or format , crashes the program.
          After I figure out the crasher I will work on form / format/ style.
          Of course I could verify the "connect" using separate test program.

          Pl45m4P 1 Reply Last reply
          0
          • A Anonymous_Banned275

            Please note - I am posting this to illustrate the problem, please please please - NO comments on my programming style!

            My primary goal is to duplicate XML "connect" using code.
            The attached code and its variations generally compiles - that is one goal done.

            HOWEVER - it crashes during run time and I SUSPECT the problem is
            after
            clicking button 11 my code builds new instance of scanner dialog and it has build-in timers . The "list" is , in theory, filed AFTER each item individual timer expire.
            BUT
            my test connect is executed immediately after the first timer expires and the "item" is changed .

            I am asking - is it possible I have a timing problem?

            Here is my current - under construction connect to copy the "list" lines.
            All it does - just compiles and cannot be tested , in existing code , due to this issue.

            #ifdef BYPASS
                // interacts with pushing buitto 11
                // keeps crashing
                
                connect(
                            this->ui->list,
                            //          SIGNAL(ui->list->currentTextChanged()),
                            SIGNAL(ui->list->itemDoubleClicked(*pItem)),
                            //           SIGNAL(DDD->ui->list->itemChanged(TEST_LABEL)),
                            //           SIGNAL(itemClicked(QListWidgetItem *)),
                            //              SIGNAL(itemChanged(TEST_LABEL)),
                            this->ui->plainTextEdit,
                            //           SLOT(DDD->ui->plainTextEdit->appendPlainText(TEST_LABEL))
                            //             SLOT(appendPlainText(TEST_LABEL))
                            SLOT(ui->plainTextEdit->appendPlainText(*pItem)));
                //           );
                
            #endif
                
                
            

            This is how it tracks when working - without the code above

            QDEBUG TRACE 
            QDEBUG TRACE TASK 
            		 END imoplement Device DiscoiveryDialog  
            
            QDEBUG TRACE TASK 
            		 find nearby BT devices 
            
            file      /media/f/QT/QT_PROJECT/TEST_PROJECT_14/mainwindow_cat_tab.cpp
            function  on_pushButton_11_clicked
            @line     236
            TEMPORARY EXIT 
            /home/f/build-TEST_PROJECT-Desktop-Debug/TEST_PROJECT exited with code 0
            

            And this is failing track

            QDEBUG TRACE 
            QDEBUG TRACE TASK 
            		 START imoplement Device DiscoveryDialog  
            
            QDEBUG TRACE TASK 
            		 find nearby BT devices 
            
            file      /media/f/QT/QT_PROJECT/TEST_PROJECT_14/mainwindow_cat_tab.cpp
            function  on_pushButton_11_clicked
            @line     206
            TEMPORARY EXIT 
            TRACE SCAN FLOW 
            			 START TOK TRACE SCAN FLOW CONSTRUCTOR 
            			DeviceDiscoveryDialog::DeviceDiscoveryDialog(QWidget *parent)
            
            
            TEMPORARY exit  @line 
            133
            The program has unexpectedly finished.
            /home/f/build-TEST_PROJECT-Desktop-Debug/TEST_PROJECT crashed
            

            Again - all I am asking - is it possible I have a timing problem?

            jsulmJ Offline
            jsulmJ Offline
            jsulm
            Lifetime Qt Champion
            wrote on last edited by
            #19

            @AnneRanch said in Please help with lambda sytax:

            function on_pushButton_11_clicked
            @line 206

            Can you show your on_pushButton_11_clicked? The crash is there at line 206.

            https://forum.qt.io/topic/113070/qt-code-of-conduct

            A 1 Reply Last reply
            1
            • A Anonymous_Banned275

              @jsulm said in Please help with lambda sytax:

              But this will also not work as QPlainTextEdit does not have a slot appendPlainText which takes a QListWidgetItem* as parameter (use new Qt5 connect syntax and a lambda)...

              I do appreciate the post.
              It may seems strange, but at this point I am NOT after "it" working.
              I just need to figure out WHY adding this "connect" , in any form or format , crashes the program.
              After I figure out the crasher I will work on form / format/ style.
              Of course I could verify the "connect" using separate test program.

              Pl45m4P Offline
              Pl45m4P Offline
              Pl45m4
              wrote on last edited by Pl45m4
              #20

              @AnneRanch

              Back to lambdas:

              You said, you are struggling to understand lambda connections correctly.
              It's not as complicated as it might look.

              • You have your sender (first argument)

                connect(ui->list,.....)
                
              • You have your sender's class + signal

                 connect(ui->list, &QListWidget::itemDoubleClicked,.....)
                
              • Then you can define a scope for your lambda

                connect(ui->list, &QListWidget::itemDoubleClicked, this,......)
                
              • the last part consists of the capture, the function or slot arguments and the actual code itself, using the passed and captured values

                • Capture

                  • "[ ]": None of the variables from current class / scope are captured and can be used inside lambda "code"
                  • " [=]": Captures everything (by value!)
                  • "[this] ": (current instance) or any combination of variables (e.g. [x, a]), to pick variables you need explicitely.
                  • "[&]" or "[ &someVar ]": Captures by reference. Changes made inside lambda will affect and change the captured variable outside the lambda as well ( Thx, @JonB )
                • Signal / Slot arguments after capture inside ( .... ), e.g. if signal sends a QListWidgetItem, you need a (QListWidgetItem *item) here.

                • lambda code inside { .... }

                  • do whatever you like and what you would put in your slot here.

              One big advantage using lambda connections is, that you can connect signals to slots (or "code"), that would be incompatible using a "direct" connection because of any reason (e.g. parameter mismatch).

              Simple example:

              // signal
              void signal(QString s);
              // slot
              void onSignalFired(int i);
              

              A direct connection of these two won't work neither using the SIGNAL(...) / SLOT( ... ) syntax
              (-> crash / error at runtime),
              nor using the function based connection &Class::signal... &Class::onSignalFired
              ( -> wont compile).

              With lambda, you can make it work:

              connect(this, &Class::signal, [] (QString s) {  onSignalFired( s.toInt() ); } ); 
              

              Instead of calling the slot, you could also skip the slot and do whatever you want to do with this string inside the lambda directly, e.g. send your number to a QLineEdit ("A" would lead to a 65, simple ASCII).

              @AnneRanch said in Please help with lambda sytax:

              Here is my current - under construction connect to copy the "list" lines.
              All it does - just compiles and cannot be tested , in existing code , due to this issue.

              ... and this is exactly where you can make use of lambdas ( as @jsulm already said ).
              Pass your QListWidgetItem from signal to your lambda, get the text from your item using text() (Qt Doc), then pass the text to QPlainTextEdit's appendPlainText(QString).


              If debugging is the process of removing software bugs, then programming must be the process of putting them in.

              ~E. W. Dijkstra

              JonBJ 1 Reply Last reply
              4
              • Pl45m4P Pl45m4

                @AnneRanch

                Back to lambdas:

                You said, you are struggling to understand lambda connections correctly.
                It's not as complicated as it might look.

                • You have your sender (first argument)

                  connect(ui->list,.....)
                  
                • You have your sender's class + signal

                   connect(ui->list, &QListWidget::itemDoubleClicked,.....)
                  
                • Then you can define a scope for your lambda

                  connect(ui->list, &QListWidget::itemDoubleClicked, this,......)
                  
                • the last part consists of the capture, the function or slot arguments and the actual code itself, using the passed and captured values

                  • Capture

                    • "[ ]": None of the variables from current class / scope are captured and can be used inside lambda "code"
                    • " [=]": Captures everything (by value!)
                    • "[this] ": (current instance) or any combination of variables (e.g. [x, a]), to pick variables you need explicitely.
                    • "[&]" or "[ &someVar ]": Captures by reference. Changes made inside lambda will affect and change the captured variable outside the lambda as well ( Thx, @JonB )
                  • Signal / Slot arguments after capture inside ( .... ), e.g. if signal sends a QListWidgetItem, you need a (QListWidgetItem *item) here.

                  • lambda code inside { .... }

                    • do whatever you like and what you would put in your slot here.

                One big advantage using lambda connections is, that you can connect signals to slots (or "code"), that would be incompatible using a "direct" connection because of any reason (e.g. parameter mismatch).

                Simple example:

                // signal
                void signal(QString s);
                // slot
                void onSignalFired(int i);
                

                A direct connection of these two won't work neither using the SIGNAL(...) / SLOT( ... ) syntax
                (-> crash / error at runtime),
                nor using the function based connection &Class::signal... &Class::onSignalFired
                ( -> wont compile).

                With lambda, you can make it work:

                connect(this, &Class::signal, [] (QString s) {  onSignalFired( s.toInt() ); } ); 
                

                Instead of calling the slot, you could also skip the slot and do whatever you want to do with this string inside the lambda directly, e.g. send your number to a QLineEdit ("A" would lead to a 65, simple ASCII).

                @AnneRanch said in Please help with lambda sytax:

                Here is my current - under construction connect to copy the "list" lines.
                All it does - just compiles and cannot be tested , in existing code , due to this issue.

                ... and this is exactly where you can make use of lambdas ( as @jsulm already said ).
                Pass your QListWidgetItem from signal to your lambda, get the text from your item using text() (Qt Doc), then pass the text to QPlainTextEdit's appendPlainText(QString).

                JonBJ Offline
                JonBJ Offline
                JonB
                wrote on last edited by JonB
                #21

                @Pl45m4
                Since you've laid this out so neatly, may I suggest you add [&] to your Capture section, and note how it differs from [=]? Because some day someone's going to need it... :)

                1 Reply Last reply
                1
                • jsulmJ jsulm

                  @AnneRanch said in Please help with lambda sytax:

                  function on_pushButton_11_clicked
                  @line 206

                  Can you show your on_pushButton_11_clicked? The crash is there at line 206.

                  A Offline
                  A Offline
                  Anonymous_Banned275
                  wrote on last edited by
                  #22

                  @jsulm said in Please help with lambda sytax:

                  @AnneRanch said in Please help with lambda sytax:

                  function on_pushButton_11_clicked
                  @line 206

                  Can you show your on_pushButton_11_clicked? The crash is there at line 206.

                  There it is.

                  I have left in all the trace / debug stuff .
                  And highlighted the line 206

                  code// scan for nearby BT devices
                  
                  void MainWindow_CAT_TAB::on_pushButton_11_clicked()
                  {
                  #ifdef TRACE
                      qDebug() << "QDEBUG TRACE ";
                      qDebug() << "QDEBUG TRACE TASK \n\t\t void MainWindow_CAT_TAB::on_pushButton_11_clicked()  \n";
                       qDebug() << "QDEBUG TRACE TASK \n\t\t find nearby BT devices \n";
                      qDebug() << "file     " << __FILE__;
                      qDebug() << "function "<<__FUNCTION__;
                      qDebug() << "@line    " << __LINE__;
                      qDebug()<<"TEMPORARY EXIT ";
                      //exit(99);
                  #endif
                  //   ui->listWidget_5->(" addItem(on_pushButton_11_clicked()");
                  //     ui->listWidget_5->(addItem(on_pushButton_11_clicked());
                               ui->listWidget_5->addItem(" addItem(on_pushButton_11_clicked()");
                               ui->listWidget_5->addItem(" addItem(on_pushButton_11_clicked()");
                               ui->listWidget_5->addItem("information_main.count())");
                  
                  
                  #ifdef TRACE
                      qDebug() << "QDEBUG TRACE ";
                      qDebug() << "QDEBUG TRACE TASK \n\t\t START imoplement Device DiscoveryDialog  \n";
                       qDebug() << "QDEBUG TRACE TASK \n\t\t find nearby BT devices \n";
                      qDebug() << "file     " << __FILE__;
                      qDebug() << "function "<<__FUNCTION__;
                      **qDebug() << "@line    " << __LINE__;**
                      qDebug()<<"TEMPORARY EXIT ";
                      //exit(99);
                  #endif
                  
                  // instatiate Devievce Discovery Dialog as in btscanner example
                  DeviceDiscoveryDialog *DDD = new DeviceDiscoveryDialog();
                  
                  DDD->startScan();  // takes time 2 seconds for each device 
                  
                  DDD->show();
                  
                  #ifdef BYPASS
                  // test add connect here
                  connect(
                              DDD->ui->list,
                   //           SIGNAL(DDD->ui->list->itemChanged(TEST_LABEL)),
                                SIGNAL(itemChanged(TEST_LABEL)),
                              DDD->ui->plainTextEdit,
                   //           SLOT(DDD->ui->plainTextEdit->appendPlainText(TEST_LABEL))
                              SLOT(appendPlainText(TEST_LABEL))
                          );
                  #endif
                  
                  
                  #ifdef TRACE
                      qDebug() << "QDEBUG TRACE ";
                      qDebug() << "QDEBUG TRACE TASK \n\t\t END imoplement Device DiscoiveryDialog  \n";
                       qDebug() << "QDEBUG TRACE TASK \n\t\t find nearby BT devices \n";
                      qDebug() << "file     " << __FILE__;
                      qDebug() << "function "<<__FUNCTION__;
                      qDebug() << "@line    " << __LINE__;
                      qDebug()<<"TEMPORARY EXIT ";
                      //exit(99);
                  #endif
                  
                  
                  }_text
                  
                  1 Reply Last reply
                  -1
                  • Christian EhrlicherC Online
                    Christian EhrlicherC Online
                    Christian Ehrlicher
                    Lifetime Qt Champion
                    wrote on last edited by
                    #23

                    @AnneRanch said in Please help with lambda sytax:

                    SIGNAL(itemChanged(TEST_LABEL)),

                    And you really want to tell us that you read at least one sentence from what we're telling you here??

                    Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                    Visit the Qt Academy at https://academy.qt.io/catalog

                    A 1 Reply Last reply
                    0
                    • Christian EhrlicherC Christian Ehrlicher

                      @AnneRanch said in Please help with lambda sytax:

                      SIGNAL(itemChanged(TEST_LABEL)),

                      And you really want to tell us that you read at least one sentence from what we're telling you here??

                      A Offline
                      A Offline
                      Anonymous_Banned275
                      wrote on last edited by
                      #24

                      Partial success.
                      Using both old and new "connect" style throws "segmentation fault" at either one.

                      It is my understanding that "connect" code placement is not critical - however my crash occurs exactly on "connect" which I have placed in a secondary dialog constructor. My main window dialog is primary.

                      RTFM implies that passing null pointer may be the problem...

                      A 1 Reply Last reply
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                      • A Anonymous_Banned275

                        Partial success.
                        Using both old and new "connect" style throws "segmentation fault" at either one.

                        It is my understanding that "connect" code placement is not critical - however my crash occurs exactly on "connect" which I have placed in a secondary dialog constructor. My main window dialog is primary.

                        RTFM implies that passing null pointer may be the problem...

                        A Offline
                        A Offline
                        Anonymous_Banned275
                        wrote on last edited by
                        #25

                        @AnneRanch DONE!
                        Ready to tackle lambda .
                        Moral of the story - stay on original issue - it was my shallow knowledge of "connect" , my wrong syntax and my implementation of "connect" - applied in wrong place.

                        Help from everybody assisting is very much appreciated.

                        62318e6e-6ee2-4e8f-b993-51ed61c92d1b-image.png

                        Pablo J. RoginaP 1 Reply Last reply
                        1
                        • A Anonymous_Banned275

                          @AnneRanch DONE!
                          Ready to tackle lambda .
                          Moral of the story - stay on original issue - it was my shallow knowledge of "connect" , my wrong syntax and my implementation of "connect" - applied in wrong place.

                          Help from everybody assisting is very much appreciated.

                          62318e6e-6ee2-4e8f-b993-51ed61c92d1b-image.png

                          Pablo J. RoginaP Offline
                          Pablo J. RoginaP Offline
                          Pablo J. Rogina
                          wrote on last edited by
                          #26

                          @AnneRanch said in Please help with lambda sytax:

                          @AnneRanch DONE!

                          great, so please don't forget to mark your post as solved!

                          Upvote the answer(s) that helped you solve the issue
                          Use "Topic Tools" button to mark your post as Solved
                          Add screenshots via postimage.org
                          Don't ask support requests via chat/PM. Please use the forum so others can benefit from the solution in the future

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