为什么qqmlcomponent :: create()返回nullptr

Question

在qqmlcomponent :: create(qqmlContext *(在什么条件下通过返回nullptr失败？该文档仅显示"如果创建失败，则返回nullptr"，没有进一步的细节。我的后端C 代码试图从以下QML实例化missagedialog：

    import QtQuick 2.0
    import QtQuick.Dialogs 1.1
    MessageDialog {
      id: messageDialog
      title: "My message"
      text: "Fill in this message from C++"
      onAccepted: {
          console.log("Knew you'd see it my way!")
          // Hide the dialog
          visible = false
      }
      Component.onCompleted: visible = true
    }

这是我的后端构造函数的片段：

    QQmlApplicationEngine engine;
    // Note that component resource is local file URL,
    // not network - no need to wait before calling create()?
    QQmlComponent *component = 
      new QQmlComponent(&engine, 
                        QStringLiteral("ui-components/MessageDialog.qml"));
    // Following call returns nullptr
    QObject *childItem = component->create();

有人知道为什么吗？谢谢！

Answer 1

我认为它找不到您的QML文件。假设您的" UI-Components/Messagedialog.QML"在QRC文件中，请尝试：

new QQmlComponent(&engine, QStringLiteral("qrc:/ui-components/MessageDialog.qml"));