更改对话框的父级禁用拖放

时间:2018-08-28 15:54:53

标签: c++ qt drag-and-drop qt5

我有一个主窗口和一个单击该按钮从该窗口打开的对话框。出于性能原因,有一个对话框高速缓存,它保留对话框的一个实例,仅在应打开对话框而不是创建新实例时才显示。在对话框中,有一个QListWidget,其中包含一些可以通过拖放更改顺序的项目。当我第一次打开对话框时,此方法有效,但是当我关闭对话框并再次打开它时,无法删除项目,我得到一个Qt::ForbiddenCursor

该问题似乎是由于在关闭对话框时调用setParent(nullptr)引起的(或者可能只是通过更改父级而引起)。如果删除此行,则可以进行拖放。但是,我需要这样做以防止对话框被父级删除,并且对话框在不同的上下文中可以具有不同的父级(这在我的简化示例中并不明显)。知道这种方法有什么问题吗?我的Qt版本是5.9.3。这可以是Qt错误吗?

MainWindow.h:

#include "ui_mainwindow.h"
#include "dialog.h"

#include <QPushButton>
#include <QMainWindow>
#include <memory>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget* parent = nullptr) : QMainWindow(parent), ui(new Ui::MainWindow)
    {
        ui->setupUi(this);

        dialog.reset(new Dialog(this));
        dialog->setAttribute(Qt::WA_DeleteOnClose, false);

        connect(ui->button, &QPushButton::pressed, [&]
        {
            dialog->setParent(this, dialog->windowFlags());
            dialog->open();
        });
    }

    ~MainWindow()
    {
        delete ui;
    }

private:
    Ui::MainWindow* ui;
    std::unique_ptr<Dialog> dialog;
};

Dialog.h:

#include "ui_dialog.h"
#include <QDialog>

class Dialog : public QDialog
{
    Q_OBJECT

public:
    explicit Dialog(QWidget* parent) : QDialog(parent), ui(new Ui::Dialog)
    {
        ui->setupUi(this);

        ui->listWidget->addItem("first");
        ui->listWidget->addItem("second");
        ui->listWidget->addItem("third");
    }

    ~Dialog()
    {
        delete ui;
    }

public slots:
    virtual void reject() override
    {
        setParent(nullptr);
        QDialog::reject();
    }

private:
    Ui::Dialog* ui;
};

Dialog.ui-具有QListWidget和拒绝按钮的简单对话框

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>Dialog</class>
 <widget class="QDialog" name="Dialog">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>548</width>
    <height>397</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Dialog</string>
  </property>
  <layout class="QVBoxLayout" name="verticalLayout">
   <item>
    <widget class="QListWidget" name="listWidget">
     <property name="dragDropMode">
      <enum>QAbstractItemView::DragDrop</enum>
     </property>
     <property name="defaultDropAction">
      <enum>Qt::MoveAction</enum>
     </property>
    </widget>
   </item>
   <item>
    <widget class="QDialogButtonBox" name="buttonBox">
     <property name="orientation">
      <enum>Qt::Horizontal</enum>
     </property>
     <property name="standardButtons">
      <set>QDialogButtonBox::Close</set>
     </property>
    </widget>
   </item>
  </layout>
 </widget>
 <resources/>
 <connections>
  <connection>
   <sender>buttonBox</sender>
   <signal>accepted()</signal>
   <receiver>Dialog</receiver>
   <slot>accept()</slot>
   <hints>
    <hint type="sourcelabel">
     <x>248</x>
     <y>254</y>
    </hint>
    <hint type="destinationlabel">
     <x>157</x>
     <y>274</y>
    </hint>
   </hints>
  </connection>
  <connection>
   <sender>buttonBox</sender>
   <signal>rejected()</signal>
   <receiver>Dialog</receiver>
   <slot>reject()</slot>
   <hints>
    <hint type="sourcelabel">
     <x>316</x>
     <y>260</y>
    </hint>
    <hint type="destinationlabel">
     <x>286</x>
     <y>274</y>
    </hint>
   </hints>
  </connection>
 </connections>
</ui>

MainWindow.ui-具有一个按钮的默认主窗口

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>432</width>
    <height>316</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget">
   <widget class="QPushButton" name="button">
    <property name="geometry">
     <rect>
      <x>40</x>
      <y>30</y>
      <width>80</width>
      <height>21</height>
     </rect>
    </property>
    <property name="text">
     <string>PushButton</string>
    </property>
   </widget>
  </widget>
  <widget class="QMenuBar" name="menuBar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>432</width>
     <height>20</height>
    </rect>
   </property>
  </widget>
  <widget class="QToolBar" name="mainToolBar">
   <attribute name="toolBarArea">
    <enum>TopToolBarArea</enum>
   </attribute>
   <attribute name="toolBarBreak">
    <bool>false</bool>
   </attribute>
  </widget>
  <widget class="QStatusBar" name="statusBar"/>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>

main.cpp

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

1 个答案:

答案 0 :(得分:2)

以下再现了问题。这确实是一个Qt错误。 OP报告了该错误:https://bugreports.qt.io/browse/QTBUG-70240

问题是因为QWidget标志处于关闭状态时Qt::Window会重新创建放置站点,从而调用QWindowsWindow::updateDropSite,这会做错事并调用setDropSiteEnabled(false)

两个等效的解决方法是:

  1. dialog->setParent(newParent)替换为:

    auto flags = dialog->windowFlags();
    dialog->setParent(newParent, {});
    dialog->setWindowFlags(flags);
    
  2. dialog->setParent(nullptr)替换为:

    dialog->setParent(nullptr, dialog->windowFlags());
    

第一个解决方法撤消了小部件的损坏状态。不需要使用第二种解决方法,即,必须始终使用该解决方法,否则必须调用一次第一种解决方法才能恢复可用的放置目标状态。

screenshot

// https://github.com/KubaO/stackoverflown/tree/master/questions/dialog-parent-dnd-52061919
#include <QtWidgets>

int main(int argc, char *argv[]) {
   QApplication app(argc, argv);

   QWidget ui;
   QVBoxLayout layout{&ui};
   QPushButton button{"Toggle List"};
   QCheckBox workaround1{"Workaround 1"};
   QCheckBox workaround2{"Workaround 2"};
   for (auto w : QWidgetList{&button, &workaround1, &workaround2}) layout.addWidget(w);
   workaround2.setChecked(true);

   QListWidget listWidget;
   Q_ASSERT(!listWidget.testAttribute(Qt::WA_DeleteOnClose));
   listWidget.setWindowFlags(Qt::Window | Qt::FramelessWindowHint);
   listWidget.setDragDropMode(QAbstractItemView::DragDrop);
   listWidget.setDefaultDropAction(Qt::MoveAction);
   for (auto s : QStringList{"first", "second", "third"}) listWidget.addItem(s);

   QObject::connect(&button, &QPushButton::pressed, [&] {
      if (!listWidget.parent()) {
         if (!workaround1.isChecked())
            listWidget.setParent(&button, listWidget.windowFlags());
         else {
            auto flags = listWidget.windowFlags();
            listWidget.setParent(&button, {});
            listWidget.setWindowFlags(flags);
         }
         listWidget.show();
      } else {
         if (!workaround2.isChecked())
            listWidget.setParent(nullptr);
         else
            listWidget.setParent(nullptr, listWidget.windowFlags());
         listWidget.close();
      }
   });

   ui.setMinimumSize(320, 200);
   ui.show();
   return app.exec();
}