qml鍵盤事件傳遞順序

qml 鍵盤事件傳遞的順序

• 思考：鍵盤事件傳遞的順序是什麼樣子的 ？

  編寫以下代碼作爲測試：

  import QtQuick 2.7
  import QtQuick.Window 2.2
  
  Rectangle{
      width: 800;
      height: 800;
      Rectangle{
          id: rect_a;
          anchors.top: parent.top;
          anchors.left: parent.left;
          width: 400;
          height: 400;
          color: focus ? "#111111" : "#db1f5b";
          focus: true;
          Keys.onPressed: {
              if(event.key === Qt.Key_A){
                  console.log("A pressed");
                  event.accepted = true;
              }
          }
          KeyNavigation.tab: rect_b;
      }
      Rectangle{
          id: rect_b;
          anchors.top: parent.top;
          anchors.right: parent.right;
          width: 400;
          height: 400;
          color: focus ? "#111111" : "#db1f5b";
          Keys.onPressed: {
              if(event.key === Qt.Key_B){
                  console.log("B pressed");
                  event.accepted = true;
              }
          }
          KeyNavigation.tab: rect_c;
      }
      Rectangle{
          id: rect_c;
          anchors.bottom: parent.bottom;
          anchors.right: parent.right;
          width: 400;
          height: 400;
          color: focus ? "#111111" : "#db1f5b";
          Keys.onPressed: {
              if(event.key === Qt.Key_C){
                  console.log("C pressed");
                  event.accepted = true;
              }
          }
          KeyNavigation.tab: rect_d;
      }
      Rectangle{
          id: rect_d;
          anchors.bottom: parent.bottom;
          anchors.left: parent.left;
          width: 400;
          height: 400;
          color: focus ? "#111111" : "#db1f5b";
          Keys.onPressed: {
              if(event.key === Qt.Key_D){
                  console.log("D pressed");
                  event.accepted = true;
              }
          }
          KeyNavigation.tab: rect_a;
      }
  
      Keys.onPressed: {
          console.log("root:" + event.key);
          event.accepted = true;
      }
  }
  
  

  得出結論：qml 中鍵盤事件傳遞是由具有焦點的那個組件，一層層向上傳遞，直到被處理或者到達根對象被而忽略。在官方文檔中也有提到

延伸：widget中事件傳遞順序又是怎樣的？

由豆子的這篇文章裏面可以知道， widget中事件的傳播是在組件層次上面的，而不是依靠類繼承機制。 參考代碼如下：

class CustomButton : public QPushButton
{
    Q_OBJECT
public:
    CustomButton(QWidget *parent) : QPushButton(parent)
    {
    }
protected:
    void mousePressEvent(QMouseEvent *event)
    {
        qDebug() << "CustomButton";
    }
};

class CustomButtonEx : public CustomButton
{
    Q_OBJECT
public:
    CustomButtonEx(QWidget *parent) : CustomButton(parent)
    {
    }
protected:
    void mousePressEvent(QMouseEvent *event)
    {
        qDebug() << "CustomButtonEx";
    }
};

class CustomWidget : public QWidget
{
    Q_OBJECT
public:
    CustomWidget(QWidget *parent) : QWidget(parent)
    {
    }
protected:
    void mousePressEvent(QMouseEvent *event)
    {
        qDebug() << "CustomWidget";
    }
};

class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0) : QMainWindow(parent)
    {
        CustomWidget *widget = new CustomWidget(this);
        CustomButton *cbex = new CustomButton(widget);
        cbex->setText(tr("CustomButton"));
        CustomButtonEx *cb = new CustomButtonEx(widget);
        cb->setText(tr("CustomButtonEx"));
        QVBoxLayout *widgetLayout = new QVBoxLayout(widget);
        widgetLayout->addWidget(cbex);
        widgetLayout->addWidget(cb);
        this->setCentralWidget(widget);
    }
protected:
    void mousePressEvent(QMouseEvent *event)
    {
        qDebug() << "MainWindow";
    }
};

思考：qml 中Window 應該如何處理鍵盤事件？

因爲Keys是專門給Item來處理鍵盤事件的，Window 無法使用Item來處理鍵盤事件，所以Window應該怎樣處理鍵盤事件 ？