Skip to content
  • Categories
  • Recent
  • Tags
  • Popular
  • Users
  • Groups
  • Search
  • Get Qt Extensions
  • Unsolved
Collapse
Brand Logo
  1. Home
  2. Qt Development
  3. QML and Qt Quick
  4. how to connect C++ signal to QML handler
Forum Updated to NodeBB v4.3 + New Features

how to connect C++ signal to QML handler

Scheduled Pinned Locked Moved Solved QML and Qt Quick
18 Posts 6 Posters 1.5k Views 4 Watching
  • Oldest to Newest
  • Newest to Oldest
  • Most Votes
Reply
  • Reply as topic
Log in to reply
This topic has been deleted. Only users with topic management privileges can see it.
  • mzimmersM mzimmers

    @LeLev right, I understand that...I just don't understand why a direct call to the getter didn't work for me.

    ODБOïO Offline
    ODБOïO Offline
    ODБOï
    wrote on last edited by ODБOï
    #8

    @mzimmers said in how to connect C++ signal to QML handler:

    I just don't understand why a direct call to the getter didn't work for me.

    Your getSynthName() is probably not a public slot nor a Q_INVOKABLE marked function, that's why you can't call it from QML ..

    By default if you declare a Q_PROPERTY and use "Refactor" option to generate getter/setter/.., the getter is just public:
    but the setter is under public slots, so you can call the setter from qml.
    If you want to call "getSynthName()" in QML then move it under "public slots". But then :

    Label {
       text: getSynthName()
    

    this will not be updated if the value of "synthName" changes in the c++ side, you will always see the initial value of "synthName"

    mzimmersM 1 Reply Last reply
    0
    • ODБOïO ODБOï

      @mzimmers said in how to connect C++ signal to QML handler:

      I just don't understand why a direct call to the getter didn't work for me.

      Your getSynthName() is probably not a public slot nor a Q_INVOKABLE marked function, that's why you can't call it from QML ..

      By default if you declare a Q_PROPERTY and use "Refactor" option to generate getter/setter/.., the getter is just public:
      but the setter is under public slots, so you can call the setter from qml.
      If you want to call "getSynthName()" in QML then move it under "public slots". But then :

      Label {
         text: getSynthName()
      

      this will not be updated if the value of "synthName" changes in the c++ side, you will always see the initial value of "synthName"

      mzimmersM Offline
      mzimmersM Offline
      mzimmers
      wrote on last edited by
      #9

      @LeLev said in how to connect C++ signal to QML handler:

      this will not refresh, you will always see the initial value of synthName.

      OK, so this is what I needed to know. So...a property will update automatically, where a reference to a function will not, right? Thanks, LeLev.

      ODБOïO 2 Replies Last reply
      0
      • mzimmersM mzimmers

        @LeLev said in how to connect C++ signal to QML handler:

        this will not refresh, you will always see the initial value of synthName.

        OK, so this is what I needed to know. So...a property will update automatically, where a reference to a function will not, right? Thanks, LeLev.

        ODБOïO Offline
        ODБOïO Offline
        ODБOï
        wrote on last edited by
        #10

        @mzimmers that is true.

        1 Reply Last reply
        0
        • mzimmersM mzimmers

          @LeLev said in how to connect C++ signal to QML handler:

          this will not refresh, you will always see the initial value of synthName.

          OK, so this is what I needed to know. So...a property will update automatically, where a reference to a function will not, right? Thanks, LeLev.

          ODБOïO Offline
          ODБOïO Offline
          ODБOï
          wrote on last edited by
          #11

          @mzimmers hi again,

          sorry i misread your initial code.. i did not see that you declare getSynthName() in QML also ..

          In this case i would simply do this :

          text: issViewModel.synthName !== "" ? issViewModel.synthName : "No Synthesis Loaded"

          no need the js function.

          1 Reply Last reply
          0
          • mzimmersM Offline
            mzimmersM Offline
            mzimmers
            wrote on last edited by
            #12

            Actually, I cleaned that up a little. I have a couple of utility JS functions now:

              function getNoSynthName() {
                var name =  "No Synthesis Loaded"
                return name;
              }
                function getSynthName() {
                  var name = issViewModel.synthName
                  if (name === "") {
                      name = getNoSynthName()
                  }
                  return name;
              }
            

            This is the only location that uses the function in issViewModel. This allows me to do this in another area:

             StyledButton {
               visible: Utils.getSynthName() !== Utils.getNoSynthName()
            ...
            
            ODБOïO 1 Reply Last reply
            0
            • mzimmersM mzimmers

              Actually, I cleaned that up a little. I have a couple of utility JS functions now:

                function getNoSynthName() {
                  var name =  "No Synthesis Loaded"
                  return name;
                }
                  function getSynthName() {
                    var name = issViewModel.synthName
                    if (name === "") {
                        name = getNoSynthName()
                    }
                    return name;
                }
              

              This is the only location that uses the function in issViewModel. This allows me to do this in another area:

               StyledButton {
                 visible: Utils.getSynthName() !== Utils.getNoSynthName()
              ...
              
              ODБOïO Offline
              ODБOïO Offline
              ODБOï
              wrote on last edited by
              #13

              @mzimmers said in how to connect C++ signal to QML handler:

              visible: Utils.getSynthName() !== Utils.getNoSynthName()

              This will be evaluated only single time, you can test it and correct me if i'm wrong.

              @mzimmers said in how to connect C++ signal to QML handler:

              Actually, I cleaned that up a little. I have a couple of utility JS functions now:
              function getNoSynthName() {
              var name = "No Synthesis Loaded"
              return name;
              }
              function getSynthName() {
              var name = issViewModel.synthName
              if (name === "") {
              name = getNoSynthName()
              }
              return name;
              }

              This is the only location that uses the function in issViewModel. This allows me to do this in another area:
              StyledButton {
              visible: Utils.getSynthName() !== Utils.getNoSynthName()
              ...

              You could replace all that by this single line that will hide the Styled Button button if the synthName == "" . And it will be reevaluated every time synthName changes...

               StyledButton {
                  visible:  issViewModel.synthName
              
              mzimmersM 1 Reply Last reply
              0
              • ODБOïO ODБOï

                @mzimmers said in how to connect C++ signal to QML handler:

                visible: Utils.getSynthName() !== Utils.getNoSynthName()

                This will be evaluated only single time, you can test it and correct me if i'm wrong.

                @mzimmers said in how to connect C++ signal to QML handler:

                Actually, I cleaned that up a little. I have a couple of utility JS functions now:
                function getNoSynthName() {
                var name = "No Synthesis Loaded"
                return name;
                }
                function getSynthName() {
                var name = issViewModel.synthName
                if (name === "") {
                name = getNoSynthName()
                }
                return name;
                }

                This is the only location that uses the function in issViewModel. This allows me to do this in another area:
                StyledButton {
                visible: Utils.getSynthName() !== Utils.getNoSynthName()
                ...

                You could replace all that by this single line that will hide the Styled Button button if the synthName == "" . And it will be reevaluated every time synthName changes...

                 StyledButton {
                    visible:  issViewModel.synthName
                
                mzimmersM Offline
                mzimmersM Offline
                mzimmers
                wrote on last edited by
                #14

                @LeLev said in how to connect C++ signal to QML handler:

                @mzimmers said in how to connect C++ signal to QML handler:

                visible: Utils.getSynthName() !== Utils.getNoSynthName()

                This will be evaluated only single time, you can test it and correct me if i'm wrong.

                It seems to update. At app startup, the button isn't visible. When I load a synthesis and return to this screen, the button is visible. The nature of the app is such that once something is loaded, it never returns to an "unloaded" state, so I can't fully test this, but it does update (at least once).

                @mzimmers said in how to connect C++ signal to QML handler:

                Actually, I cleaned that up a little. I have a couple of utility JS functions now:
                function getNoSynthName() {
                var name = "No Synthesis Loaded"
                return name;
                }
                function getSynthName() {
                var name = issViewModel.synthName
                if (name === "") {
                name = getNoSynthName()
                }
                return name;
                }

                This is the only location that uses the function in issViewModel. This allows me to do this in another area:
                StyledButton {
                visible: Utils.getSynthName() !== Utils.getNoSynthName()
                ...

                You could replace all that by this single line that will hide the Styled Button button if the synthName == "" . And it will be reevaluated every time synthName changes...

                 StyledButton {
                    visible:  issViewModel.synthName
                

                Not quite. When no synthesis is loaded, I need that value "No Synthesis Loaded" because I use it in two screens.

                ODБOïO 1 Reply Last reply
                0
                • mzimmersM mzimmers

                  @LeLev said in how to connect C++ signal to QML handler:

                  @mzimmers said in how to connect C++ signal to QML handler:

                  visible: Utils.getSynthName() !== Utils.getNoSynthName()

                  This will be evaluated only single time, you can test it and correct me if i'm wrong.

                  It seems to update. At app startup, the button isn't visible. When I load a synthesis and return to this screen, the button is visible. The nature of the app is such that once something is loaded, it never returns to an "unloaded" state, so I can't fully test this, but it does update (at least once).

                  @mzimmers said in how to connect C++ signal to QML handler:

                  Actually, I cleaned that up a little. I have a couple of utility JS functions now:
                  function getNoSynthName() {
                  var name = "No Synthesis Loaded"
                  return name;
                  }
                  function getSynthName() {
                  var name = issViewModel.synthName
                  if (name === "") {
                  name = getNoSynthName()
                  }
                  return name;
                  }

                  This is the only location that uses the function in issViewModel. This allows me to do this in another area:
                  StyledButton {
                  visible: Utils.getSynthName() !== Utils.getNoSynthName()
                  ...

                  You could replace all that by this single line that will hide the Styled Button button if the synthName == "" . And it will be reevaluated every time synthName changes...

                   StyledButton {
                      visible:  issViewModel.synthName
                  

                  Not quite. When no synthesis is loaded, I need that value "No Synthesis Loaded" because I use it in two screens.

                  ODБOïO Offline
                  ODБOïO Offline
                  ODБOï
                  wrote on last edited by
                  #15

                  @mzimmers said in how to connect C++ signal to QML handler:

                  Not quite. When no synthesis is loaded, I need that value "No Synthesis Loaded" because I use it in two screens.

                  if you need the functions in other places then use them, but in this particular case when you write

                   StyledButton {
                     visible: Utils.getSynthName() !== Utils.getNoSynthName()
                  

                  you are hiding that button if synthName == ""

                  This does the same, but is much simpler.

                  StyledButton {
                      visible:  issViewModel.synthName
                  
                  mzimmersM 1 Reply Last reply
                  0
                  • ODБOïO ODБOï

                    @mzimmers said in how to connect C++ signal to QML handler:

                    Not quite. When no synthesis is loaded, I need that value "No Synthesis Loaded" because I use it in two screens.

                    if you need the functions in other places then use them, but in this particular case when you write

                     StyledButton {
                       visible: Utils.getSynthName() !== Utils.getNoSynthName()
                    

                    you are hiding that button if synthName == ""

                    This does the same, but is much simpler.

                    StyledButton {
                        visible:  issViewModel.synthName
                    
                    mzimmersM Offline
                    mzimmersM Offline
                    mzimmers
                    wrote on last edited by
                    #16

                    @LeLev I suppose it's a matter of coding taste. I personally don't care to implicitly determine a boolean based on the contents of a string (or any other variable; I prefer the comparison to be made explicitly. More verbose, but (IMO) easier for the new reader to understand. I do appreciate the input, though.

                    ODБOïO 1 Reply Last reply
                    0
                    • mzimmersM mzimmers

                      @LeLev I suppose it's a matter of coding taste. I personally don't care to implicitly determine a boolean based on the contents of a string (or any other variable; I prefer the comparison to be made explicitly. More verbose, but (IMO) easier for the new reader to understand. I do appreciate the input, though.

                      ODБOïO Offline
                      ODБOïO Offline
                      ODБOï
                      wrote on last edited by ODБOï
                      #17

                      @mzimmers said in how to connect C++ signal to QML handler:

                      I prefer the comparison to be made explicitly

                      you can write it in more explicit way, to me this is simpler

                      StyledButton {
                          visible:  issViewModel.synthName != ""
                      

                      than

                      StyledButton {
                          visible:  Utils.getSynthName() !== Utils.getNoSynthName()  
                      

                      @mzimmers said in how to connect C++ signal to QML handler:

                      I suppose it's a matter of coding taste.

                      To me it is not just a mater of taste.
                      you are calling 2/3 functions where you could just write one simple js expression...

                      Also because one solution will update/refresh dynamically but the other will not
                      [edit] i was wrong here, actually both solution will update, as explained by @GrecKo

                      GrecKoG 1 Reply Last reply
                      0
                      • ODБOïO ODБOï

                        @mzimmers said in how to connect C++ signal to QML handler:

                        I prefer the comparison to be made explicitly

                        you can write it in more explicit way, to me this is simpler

                        StyledButton {
                            visible:  issViewModel.synthName != ""
                        

                        than

                        StyledButton {
                            visible:  Utils.getSynthName() !== Utils.getNoSynthName()  
                        

                        @mzimmers said in how to connect C++ signal to QML handler:

                        I suppose it's a matter of coding taste.

                        To me it is not just a mater of taste.
                        you are calling 2/3 functions where you could just write one simple js expression...

                        Also because one solution will update/refresh dynamically but the other will not
                        [edit] i was wrong here, actually both solution will update, as explained by @GrecKo

                        GrecKoG Offline
                        GrecKoG Offline
                        GrecKo
                        Qt Champions 2018
                        wrote on last edited by
                        #18

                        @LeLev said in how to connect C++ signal to QML handler:

                        Also because one solution will update/refresh dynamically but the other will not
                        visible: issViewModel.synthName != "" // this will update dinamially
                        visible: Utils.getSynthName() !== Utils.getNoSynthName() // this will not update dinamially.Only evaluated 1 time on component creation

                        That's incorrect. Both will updated dynamically since the functions are evaluated in QML. Were the functions implemented in C++, the QML would have no way to figure out the properties dependencies but that that's not the case here.

                        1 Reply Last reply
                        0

                        • Login

                        • Login or register to search.
                        • First post
                          Last post
                        0
                        • Categories
                        • Recent
                        • Tags
                        • Popular
                        • Users
                        • Groups
                        • Search
                        • Get Qt Extensions
                        • Unsolved