QAbstractItemModel 的顶级项目未显示在 QTreeView 中

Question

为什么

QTreeView

中只显示标题，而不显示项目（字符串数据为“Item1”）本身？

通过

setModel()

上的

QTreeView

正确设置模型，并且未设置其他属性。

我使用了 QT 6.5.2 和 C++20。

最小的可编译示例：

CMakeLists.txt

cmake_minimum_required(VERSION 3.21)

project(DemoModel VERSION 1.0
        DESCRIPTION "DemoModel"
        LANGUAGES CXX)

set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)
set(CMAKE_AUTOUIC ON)

add_executable(DemoModel WIN32
    demo_model.h)

if ( MSVC )
    set_target_properties(DemoModel PROPERTIES LINK_FLAGS "/ignore:4099")
    target_compile_options(DemoModel PRIVATE "/WX")
endif()

set_target_properties(DemoModel PROPERTIES
  CXX_STANDARD 20
  CXX_STANDARD_REQUIRED YES
  CXX_EXTENSIONS NO
)
set_target_properties(DemoModel PROPERTIES
  ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/lib"
  LIBRARY_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/lib"
  RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/bin"
)

include(CheckIPOSupported)
check_ipo_supported(RESULT result)
if(result)
  set_target_properties(DemoModel PROPERTIES INTERPROCEDURAL_OPTIMIZATION TRUE)
endif()

find_package(Qt6 REQUIRED COMPONENTS Core Gui Widgets)
qt_standard_project_setup()
target_link_libraries(DemoModel PRIVATE Qt6::Core)
target_link_libraries(DemoModel PRIVATE Qt6::Gui)
target_link_libraries(DemoModel PRIVATE Qt6::Widgets)

target_include_directories(DemoModel PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/include")
target_sources(DemoModel PRIVATE
  #Souces
  "${CMAKE_CURRENT_SOURCE_DIR}/main.cpp"
  "${CMAKE_CURRENT_SOURCE_DIR}/demo_model.h"
)

demo_model.h

#pragma once

#include <QAbstractItemModel>

class DemoModel : public QAbstractItemModel
{
    Q_OBJECT
public:
    DemoModel( QObject *parent = nullptr );

    QVariant data(const QModelIndex &index, int role) const override;
    QVariant headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const override;
    QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const override;
    QModelIndex parent(const QModelIndex &index) const override;
    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
    int columnCount(const QModelIndex &parent = QModelIndex()) const override;
    Qt::ItemFlags flags(const QModelIndex &index) const override;
};

main.cpp

#include <QApplication>
#include <QTreeView>
#include <QHBoxLayout>

#include "demo_model.h"

DemoModel::DemoModel( QObject *parent ) : QAbstractItemModel( parent ) {}

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

    return QAbstractItemModel::flags( index );
}

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

    return "Item1";
}

QVariant DemoModel::headerData( int section, Qt::Orientation orientation, int role ) const
{
    if ( orientation == Qt::Horizontal && role == Qt::DisplayRole )
        return "Items";

    return QVariant();
}

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

    if ( !parent.isValid() )
    {
        if ( row == 0 && column == 0 )
            return createIndex( row, column, nullptr );
    }

    return QModelIndex();
}

QModelIndex DemoModel::parent( const QModelIndex &index ) const
{
    return QModelIndex();
}

int DemoModel::rowCount( const QModelIndex &parent ) const
{
    if ( !parent.isValid() )
        return 1;

    return 0;
}

int DemoModel::columnCount( const QModelIndex &parent ) const
{
    return 1;
}

class MainWindow : public QWidget
{
public:
    explicit MainWindow( QWidget *parent = nullptr ) : QWidget( parent )
    {
        auto *demoModel = new DemoModel();
        auto *demoView  = new QTreeView();
        demoView->setModel( demoModel );

        auto layout = new QHBoxLayout;
        layout->addWidget( demoView );
        setLayout( layout );
        setWindowTitle( tr( "DemoModel" ) );
    }
};

auto main( int argc, char *argv[] ) -> int
{
    QApplication app( argc, argv );
    app.setAttribute( Qt::AA_DontCreateNativeWidgetSiblings );
    MainWindow window;
    window.show();
    return app.exec();
}

Answer 1

看来无论角色如何，在数据方法中返回“Item1”都不是一个好主意。如果您现在将字符串的返回限制为显示角色，则所有内容都会正确显示。

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

    if ( role == Qt::DisplayRole )
        return "Item1";

    return QVariant();
}