qt-everywhere-src-5.15.1/qtbase/src/gui/kernel/qdnd.cpp

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#include "qdnd_p.h"

#include "qguiapplication.h"
#include <ctype.h>
#include <qpa/qplatformdrag.h>
#include <qpa/qplatformintegration.h>
#include <private/qguiapplication_p.h>

QT_BEGIN_NAMESPACE

// the universe's only drag manager
QDragManager *QDragManager::m_instance = nullptr;

QDragManager::QDragManager()
    : QObject(qApp), m_currentDropTarget(nullptr),
      m_platformDrag(QGuiApplicationPrivate::platformIntegration()->drag()),
      m_object(nullptr)
{
    Q_ASSERT(!m_instance);
}

QDragManager::~QDragManager()
{
    m_instance = nullptr;
}

QDragManager *QDragManager::self()
{
    if (!m_instance && !QGuiApplication::closingDown())
        m_instance = new QDragManager;
    return m_instance;
}

QObject *QDragManager::source() const
{
    if (m_object)
        return m_object->source();
    return nullptr;
}

void QDragManager::setCurrentTarget(QObject *target, bool dropped)
{
    if (m_currentDropTarget == target)
        return;

    m_currentDropTarget = target;
    if (!dropped && m_object) {
        m_object->d_func()->target = target;
        emit m_object->targetChanged(target);
    }
}

QObject *QDragManager::currentTarget() const
{
    return m_currentDropTarget;
}

Qt::DropAction QDragManager::drag(QDrag *o)
{
    if (!o || m_object == o)
         return Qt::IgnoreAction;

    if (!m_platformDrag || !o->source()) {
        o->deleteLater();
        return Qt::IgnoreAction;
    }

    if (m_object) {
        qWarning("QDragManager::drag in possibly invalid state");
        return Qt::IgnoreAction;
    }

    m_object = o;

    m_object->d_func()->target = nullptr;

    QGuiApplicationPrivate::instance()->notifyDragStarted(m_object.data());
    const Qt::DropAction result = m_platformDrag->drag(m_object);
    if (!m_object.isNull() && !m_platformDrag->ownsDragObject())
        m_object->deleteLater();

    m_object.clear();
    return result;
}

QT_END_NAMESPACE