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Show different qml ui from c++

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  • mrjjM Offline
    mrjjM Offline
    mrjj
    Lifetime Qt Champion
    wrote on last edited by
    #2

    Hi
    What about emit signal from the login screen to the c++ program if login is valid?
    Then c++ can show next QML file.
    http://wisol.ch/w/articles/2014-12-15-qt-signal-slots-qml-cpp/

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    0
    • F Offline
      F Offline
      firefox
      wrote on last edited by
      #3

      HI mrji,

      I was trying to do that. My C++ class emits a signal if login is successful which is connected to a C++ slot which tries engine.load(path to new qml file). But it doesn't work. Is it correct way to show new qml UI?

      mrjjM 1 Reply Last reply
      0
      • F firefox

        HI mrji,

        I was trying to do that. My C++ class emits a signal if login is successful which is connected to a C++ slot which tries engine.load(path to new qml file). But it doesn't work. Is it correct way to show new qml UI?

        mrjjM Offline
        mrjjM Offline
        mrjj
        Lifetime Qt Champion
        wrote on last edited by
        #4

        @firefox
        Are u sure the slot is called ?

        Can engine.load return some status ?

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        • F Offline
          F Offline
          firefox
          wrote on last edited by
          #5

          This is my slot that gets called when login is succesful.

          void Login::showClient()
          {
              cout<<"trying to load client"<<endl;
              QQmlApplicationEngine engine;
              engine.load(QUrl(QStringLiteral("qrc:/BuddyList.qml")));
          
          }
          

          my cout statement gets printed that means slot is indeed getting called.
          Should I really be creating a new engine and load the qml file is there an elegant way of doing it?

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          • jsulmJ Offline
            jsulmJ Offline
            jsulm
            Lifetime Qt Champion
            wrote on last edited by
            #6

            engine is a local variable and gets destroyed when showClient() finishes.

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

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            1
            • mrjjM Offline
              mrjjM Offline
              mrjj
              Lifetime Qt Champion
              wrote on last edited by
              #7

              @firefox said:
              well this seems wrong as
              QQmlApplicationEngine engine;
              is a local variable and will be deleted as soon as function ends.

              Cant you use the original engine that loads the login?

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              1
              • F Offline
                F Offline
                firefox
                wrote on last edited by firefox
                #8

                Thanks,

                that was a brain fart on my side.
                This is how my slot looks like now

                void Login::showClient()
                {
                    emit loginSuccessful();
                    cout<<"trying to load client"<<endl;
                    Q_ASSERT(engine);
                    engine->load(QUrl(QStringLiteral("qrc:/BuddyList.qml")));
                }
                

                Now the problem is login.qml is still shown even after loading new qml file to same engine.
                To overcome this, I added a new signal that is emitted when login is succesful that is picked by login.qml and set's it visible property to false.

                But this seems like a hack and I'm guessing the login.qml instance still lingers around in memory. Do you guys suggest any better way to unload the login.qml from engine?

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                • mrjjM Offline
                  mrjjM Offline
                  mrjj
                  Lifetime Qt Champion
                  wrote on last edited by
                  #9

                  Hi

                  • that was a brain fart on my side.
                    Its a classic fart :)

                  Im have not used QML so much to know if there is better way
                  and not sure how to unload using engine.

                  We can try to ask @Wieland ;)

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                  0
                  • F Offline
                    F Offline
                    firefox
                    wrote on last edited by
                    #10

                    @mrjj

                    Thanks mrjj.
                    I'm new to this forum. How to include @Wieland to this discussion? Will he be getting a notification if I @mention him.

                    mrjjM 1 Reply Last reply
                    0
                    • F firefox

                      @mrjj

                      Thanks mrjj.
                      I'm new to this forum. How to include @Wieland to this discussion? Will he be getting a notification if I @mention him.

                      mrjjM Offline
                      mrjjM Offline
                      mrjj
                      Lifetime Qt Champion
                      wrote on last edited by
                      #11

                      @firefox
                      yes he will :)
                      Hopefully he dont mind :)

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                      • ? Offline
                        ? Offline
                        A Former User
                        wrote on last edited by
                        #12

                        Hi, I will look into this tomorrow, I promise!

                        1 Reply Last reply
                        1
                        • ? Offline
                          ? Offline
                          A Former User
                          wrote on last edited by A Former User
                          #13

                          Ok, this is what I would do:

                          1. backend in C++, exposed to QtQuick
                          2. main.qml with the main application window
                          3. Login.qml with the login window
                          4. In main.cpp: use QQmlApplicationEngine and engine.load() to show main.qml as always
                          5. main.qml has its visible property set to false on startup
                          6. Login.qml is a Window from QtQuick.Window 2.0
                          7. main.qml has such a login window as a child
                          8. on startup the login window's visible property is set to true

                          -> on startup both the main window and the login window are loaded but only the login window is visible

                          1. the backend has one slot and two signals
                          2. the login window calls the backend's slot after the user has entered her password and clicked on a login button
                          3. the backend's slot takes the entered password as argument and checks if it's correct
                          4. if the password is correct the backend emits a "loginOk" signal, otherwise it emits a "loginFailed" signal
                          5. the login window has a slot connected to the backend's loginFailed signal. if it receives this signal it will tell the user to try it again

                          -> if password is wrong login window says "try again"

                          1. the main window has a slot connected to the backends loginOk signal
                          2. if it receives this signal it will make the login window invisible and make itself (the main window) visible

                          If you like the idea then I can post a working example.
                          Cheers!

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                          3
                          • ? Offline
                            ? Offline
                            A Former User
                            wrote on last edited by
                            #14

                            Oh, I forgot this: If you're really concerned about the memory the login window consumes then you can also create and destroy the login window dynamically from within main.qml.

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                            1
                            • F Offline
                              F Offline
                              firefox
                              wrote on last edited by
                              #15

                              @Wieland
                              Thank you. I like your idea. I'm new to qml but I'd like to try it out myself first and see if I can get it working.
                              I'd like to know about creating and destroying the login window dynamically. I think I would need it as the application is a chat client and I'd require to create and destroy chat windows.

                              ? 1 Reply Last reply
                              0
                              • F firefox

                                @Wieland
                                Thank you. I like your idea. I'm new to qml but I'd like to try it out myself first and see if I can get it working.
                                I'd like to know about creating and destroying the login window dynamically. I think I would need it as the application is a chat client and I'd require to create and destroy chat windows.

                                ? Offline
                                ? Offline
                                A Former User
                                wrote on last edited by
                                #16

                                @firefox The official docs have the necessary info for dynamic creation / destruction, see: Dynamic QML Object Creation from JavaScript.

                                kshegunovK 1 Reply Last reply
                                0
                                • ? A Former User

                                  @firefox The official docs have the necessary info for dynamic creation / destruction, see: Dynamic QML Object Creation from JavaScript.

                                  kshegunovK Offline
                                  kshegunovK Offline
                                  kshegunov
                                  Moderators
                                  wrote on last edited by kshegunov
                                  #17

                                  @Wieland
                                  Isn't this a fairly complex solution for quite the simple problem?
                                  (I'm not arguing about the solution itself, only pondering about QML)

                                  Read and abide by the Qt Code of Conduct

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                                  0
                                  • F Offline
                                    F Offline
                                    firefox
                                    wrote on last edited by firefox
                                    #18

                                    @Wieland

                                    I created a login.qml and added it as child of main.qml and visible set to true
                                    main.qml has it's visible property set to false and when it receives loginSuccesful signal it's visible is set to true and login's visible is set to false.

                                    ApplicationWindow {
                                        id: mainClientId
                                        visible: false
                                        height: 640
                                        width:480
                                        minimumHeight: 500
                                        minimumWidth: 400
                                        color: "#cecece"
                                    
                                    
                                        Login {   //This is defined as window in Login.qml
                                            visible: true
                                            id: loginClientId
                                        }
                                    
                                    
                                        Connections {
                                            target: loginClass
                                            onLoginSuccessful: {
                                                console.log("in Connections")
                                                mainClientId.visible = true
                                                loginClientId.visible = false
                                            }
                                    
                                        }
                                    }
                                    

                                    But since the parent's visible property is false, even login window doesn't show up when i run the application. Am I doing it right?

                                    @kshegunov what do you suggest here?

                                    kshegunovK 1 Reply Last reply
                                    0
                                    • F firefox

                                      @Wieland

                                      I created a login.qml and added it as child of main.qml and visible set to true
                                      main.qml has it's visible property set to false and when it receives loginSuccesful signal it's visible is set to true and login's visible is set to false.

                                      ApplicationWindow {
                                          id: mainClientId
                                          visible: false
                                          height: 640
                                          width:480
                                          minimumHeight: 500
                                          minimumWidth: 400
                                          color: "#cecece"
                                      
                                      
                                          Login {   //This is defined as window in Login.qml
                                              visible: true
                                              id: loginClientId
                                          }
                                      
                                      
                                          Connections {
                                              target: loginClass
                                              onLoginSuccessful: {
                                                  console.log("in Connections")
                                                  mainClientId.visible = true
                                                  loginClientId.visible = false
                                              }
                                      
                                          }
                                      }
                                      

                                      But since the parent's visible property is false, even login window doesn't show up when i run the application. Am I doing it right?

                                      @kshegunov what do you suggest here?

                                      kshegunovK Offline
                                      kshegunovK Offline
                                      kshegunov
                                      Moderators
                                      wrote on last edited by
                                      #19

                                      @firefox
                                      I don't work with QML, so I'm not suggesting anything. I was simply surprised it looks so complicated in QML (for the widgets module, which I use, what you're asking would be a two line snippet).

                                      Read and abide by the Qt Code of Conduct

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                                      0
                                      • F Offline
                                        F Offline
                                        firefox
                                        wrote on last edited by
                                        #20

                                        Okay, Just realized the mistake.

                                        This is how main.qml looks now and it works.

                                        
                                        Item {
                                        
                                            Client {
                                                id: clientId
                                                visible:false
                                            }
                                        
                                            Login {
                                                id: loginId
                                                visible: true
                                            }
                                        
                                        
                                            Connections {
                                                target: loginClass
                                                onLoginSuccessful: {
                                                    console.log("in Connections")
                                                    clientId.visible = true
                                                    loginId.visible = false
                                                }
                                        
                                            }
                                        }
                                        
                                        
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                                        0
                                        • F Offline
                                          F Offline
                                          firefox
                                          wrote on last edited by firefox
                                          #21

                                          folks,

                                          got another problem

                                          I have this signal messageReceivedToQml emitted by my c++ backend when a new message arrives.
                                          And I connected to my qml like this

                                          Connections {
                                                  target: loginClass
                                                  onMessageReceivedToQml: {
                                                      console.log("in client connections")
                                                      Script.createChatWindow()
                                                  }
                                              }
                                          

                                          my createChatWindow javascript function is

                                          function createChatWindow() {
                                              console.log("creating chat window");
                                              var chatWindow2 = Qt.createComponent("ChatWindow.qml");
                                              chatWindow2.createObject(clientId);
                                          }
                                          
                                          

                                          the log 'creating chat window' gets printed when i receive a message but the chat window created is not visible. Am I missing something here?

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