c++ - 如何从 C++ 访问特定 QML 控件的事件

Question

有没有一种方法可以从 C++ 访问 QML 控件(例如按钮)的信号(例如 clicked())。假设我有那个特定控件的内存地址。我只想从 C++ 代码模拟点击事件。

Answer 1

简单。您只需在具有 QObject 基础的 C++ 对象中创建一个插槽，确保其注册为 QML 类型，然后在 QML 文档中“实例化”它，并使用 connect 通过 QML 将所需信号连接到 C++ 对象() 并从 C++ 端处理逻辑。

例子:

我有一个矩形，我想从中获取 onWidthChanged 信号并在我的类 ShapeTracker 中使用它，它跟踪形状何时发生变化或其他什么

在 main.cpp 中:

#include "shapetracker.h"

int main(int argc, char *argv[])
{

    QGuiApplication app(argc, argv);



  QQmlApplicationEngine engine;



   /*  this is where you register ShapeTracker as a QML type that can be 
        accessed through the QML engine even though its a C++ QObject */

    qmlRegisterType<ShapeTracker>("my_cpp_classes", 1, 0, "ShapeTracker");




  engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
   return app.exec();
 } 

然后在

主.qml

import QtQuick 2.6



/* import the C++ class you registered into this QML document */

import my_cpp_classes 1.0


Window {
    visible: true
    Item {


        /*  set up a parent item that has a signal which is exposed to 
             the ShapeTracker object and the Rectangle you want to track */
        id:  myRootItem    
        signal  rectangleChanged(var newWidth)



        /* Heres our special Rectangle from QML that will send a signal when
           its width changes */
        Rectangle {
           id: specialRectangle
            width:  250


         /*  send the signal rectangleChanged(width) from our parent item 
             root item whenever width changes
            */
            onWidthChanged:  function() { rectangleChanged(width);  }

        }


        /*  Special Button that when clicked enlarges the Rectangle but 
             10px */
        Button {
             id: mySpecialButton
             onClicked:  {  click_handler(mouse); }

             function click_handler(mouse): {
                  if (specialRectangle.width < 500) 
                      specialRectangle.width += 10;
             }
        }



        /* Heres the actual ShapeTracker instance, which exists 
          as a  QObject inside of the QML context, but has its methods 
          which   are declared in C++, and exposed to the QML engine */
        ShapeTracker {
            id: myShapeTracker


            /* similar to a constructor, but more like a callback */
           Component.onCompleted: {


           /*  connect our signal from the parent root Item  called 
              "rectangleChanged"  to the ShapeTracker's  Slot  called 
             "myRectangleChangeHandler"      */
                   myRootItem.rectangleChanged.connect(myShapeTracker.myRectangleChangeHandler);


              /* connect send_mouse_click to the click_handler of 
                 the button */                        
               myShapeTracker.send_mouse_click.connect(mySpecialButton.click_handler)

                }

       }

    }
}

在 shapetracker.h 中，您只需添加一个名为 myRectangleChangeHandler 的新插槽，只要它通过 QML 发送并通过 C++ 处理，它就会收到该信号

class ShapeTracker : public QObject {
    Q_OBJECT
public:
    ShapeTracker(QObject *parent = 0 );

signal: 

    void send_mouse_click(QMouseEvent *event);


public slots:
    void myRectangleChangeHandler(QVariant newWidth) {
           /*  Perform a mouse click on our QML Object mySpecialButton 
               using QQuickItem::mousePressEvent  and sending it via 
               signal back to QML */


           QMouseEvent myEvent(QEvent::MouseButtonPress, QPointF(1,1), Qt::LeftButton, Qt::LeftButton, Qt::NoModifier);

          QMouseEvent* pressEvent = QQuickItem::mousePressEvent(&myEvent);

           emit send_mouse_click(pressEvent);


    }

};

---

总而言之，

您将 C++ QObject 公开给 QML，然后使用

  object.signal.connect(cppObject.desired_slot)  

为了连接它们——所有额外的东西都是为了一个功能示例，以防以后有人需要它

实际上，您甚至不需要这个功能，因为在 onClick 事件中发生的任何事情都可以很容易地放入任何其他属性中，例如

Rectangle {
       id: rect
       signal customClick(var var1)
       onCustomClick : {  console.log(var1);   } 
    }

   Item {
         rect.customClick(1);   
    }