Qt Qml Error: Unable to assign [undefined] to QString in a subclassed QAbstractItemModel for Qml TreeView

Question

我尝试为 Qml TreeView 创建一个自定义模块，我使用 Simpel Treeview Example 作为基础，但我总是得到 "unabe to assign [undefined] to QString".

这里有一些你可能需要的信息：

Displayed view

Qml:

import QtQuick 2.0
import QtQuick.Controls 1.4
import cci.screenshotCreator.StructureDataModel 1.0

TreeView  {
    id: root
    state: "closed"
    TableViewColumn {
       role: "folderName"
       title: "Ordnerstruktur"
    }
    model: StructureDataModel{
        id: dataModel
    }

    itemDelegate: Item {
        height: 30
        Rectangle {
           id: rectangle
           color: styleData.selected ? "lightgray" : "#ffffff"
           border.width: styleData.selected ? 2 : 1
           border.color: styleData.selected ? "lightblue" : "#ababab"
           anchors.fill: parent
        }

    Text {
        id: folderText
        text: dataModel.folderName
        fontSizeMode: Text.Fit
        anchors.fill: parent
        font.pointSize: 12
        verticalAlignment: Text.AlignLeft
    }

C++:

#include "structuredatamodel.h"

structureDataModel::structureDataModel(QObject *parent)
    : QAbstractItemModel(parent)
{
    QList<QVariant> rootData;
    rootData << "/";
    rootItem = new StructureItem(rootData);
    setupModelData(rootItem);
}

structureDataModel::~structureDataModel()
{
    delete rootItem;
}

QModelIndex structureDataModel::index(int row, int column, const QModelIndex &parent) const
{
    if(!hasIndex(row, column, parent))
        return QModelIndex();

    StructureItem *parentItem;

    if(!parent.isValid())
        parentItem = rootItem;
    else
        parentItem = static_cast<StructureItem*>(parent.internalPointer());

    StructureItem *childItem = parentItem->child(row);
    if(childItem)
        return createIndex(row, column, childItem);
    else
        return QModelIndex();
}

QHash<int, QByteArray> structureDataModel::roleNames() const
{
    QHash<int, QByteArray> roles;
    roles[structureRoles::folderName] = "folderName";
    return roles;
}

QModelIndex structureDataModel::parent(const QModelIndex &index) const
{
    if(!index.isValid())
        return QModelIndex();

    StructureItem *childItem = static_cast<StructureItem*>(index.internalPointer());
    StructureItem *parentItem = childItem->parentItem();

    if (parentItem == rootItem)
        return QModelIndex();

    return createIndex(parentItem->row(), 0, parentItem);
}

int structureDataModel::rowCount(const QModelIndex &parent) const
{
    StructureItem *parentItem;
    if(parent.column() > 0)
        return 0;

    if(!parent.isValid())
        parentItem = rootItem;
    else
        parentItem = static_cast<StructureItem*>(parent.internalPointer());

    return parentItem->childCount();
}

int structureDataModel::columnCount(const QModelIndex &parent) const
{
    if(parent.isValid())
        return static_cast<StructureItem*>(parent.internalPointer())->columnCount();
    else
        return rootItem->columnCount();
}

QVariant structureDataModel::data(const QModelIndex &index, int role) const
{
    if(!index.isValid())
        return QVariant();

    if(role != structureRoles::folderName)
        return QVariant();

    StructureItem *item = static_cast<StructureItem*>(index.internalPointer());


    return item->data(index.column()).toString();
}


Qt::ItemFlags structureDataModel::flags(const QModelIndex &index) const
{
    if(!index.isValid())
        return 0;

    return QAbstractItemModel::flags(index);
}

QVariant structureDataModel::headerData(int section, Qt::Orientation orientation, int role) const
{
    if (orientation == Qt::Horizontal && role == structureRoles::folderName)
        return rootItem->data(section);

    return QVariant();
}


void structureDataModel::setupModelData(StructureItem *parent)
{
    QList<QVariant> data;
    data << "Test";
    StructureItem *child = new StructureItem(data, parent);
    parent->appendChild(child);
}

StructureItem 与 TreeItem 相同（只是名称不同 :)）我制作了自己的 setupModelData，以便模型只有一行作为根点。后来我想要一个可编辑的树视图，但现在一个工作的只读树视图现在应该可以工作了。我怀疑它与 setupModelData 或使 c++ 对 qml 可见有关。

PS：我添加了 qmlRegisterType("cci.screenshotCreator.StructureDataModel", 1, 0, "StructureDataModel");到主文件注册 cpp class.

用于测试的最小应用程序： https://pastebin.com/u/Klidrack（我的 pastebin 配置文件的所有文件）:)

Answer 1

哦，第一眼没看出来。 ListView 和 TreeView 在 QML 中的委托组件之间存在差异。在 TreeView 中，您有 itemDelegate 并且所有数据都通过 styleData 属性展开。

在你的情况下，这应该是这样的：

itemDelegate: Item
    {
        height: 30
        Rectangle
        {
            id: rectangle
            color: styleData.selected ? "lightgray" : "#ffffff"
            border.width: styleData.selected ? 2 : 1
            border.color: styleData.selected ? "lightblue" : "#ababab"
            anchors.fill: parent
        }

        Text
        {
            id: folderText
            text: styleData.value
            fontSizeMode: Text.Fit
            anchors.fill: parent
            font.pointSize: 12
            verticalAlignment: Text.AlignLeft
        }
    }

Qt Qml Error: Unable to assign [undefined] to QString in a subclassed QAbstractItemModel for Qml TreeView

Qt Qml Error: Unable to assign [undefined] to QString in a subclassed QAbstractItemModel for Qml TreeView

c++

treeview

qt

qt-creator

qml