QScrollArea和QVBoxLayout问题与动态添加的小部件

Question

我遇到了一个奇怪的问题，动态添加了小部件到QScrollArea中包含的QVBoxLayout。如果我添加小部件它按预期工作，但是在删除所有小部件后，屏幕上仍然存在一些工件。见截图：

请参阅下面的代码：

ui_mainwindow.h

/********************************************************************************
** Form generated from reading UI file 'mainwindow.ui'
**
** Created by: Qt User Interface Compiler version 5.2.0
**
** WARNING! All changes made in this file will be lost when recompiling UI file!
********************************************************************************/

#ifndef UI_MAINWINDOW_H
#define UI_MAINWINDOW_H

#include <QtCore/QVariant>
#include <QtWidgets/QAction>
#include <QtWidgets/QApplication>
#include <QtWidgets/QButtonGroup>
#include <QtWidgets/QHBoxLayout>
#include <QtWidgets/QHeaderView>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QMenuBar>
#include <QtWidgets/QPushButton>
#include <QtWidgets/QScrollArea>
#include <QtWidgets/QStatusBar>
#include <QtWidgets/QToolBar>
#include <QtWidgets/QVBoxLayout>
#include <QtWidgets/QWidget>

QT_BEGIN_NAMESPACE

class Ui_MainWindow
{
public:
    QWidget *centralWidget;
    QVBoxLayout *verticalLayout_2;
    QScrollArea *scrollArea;
    QWidget *scrollAreaWidgetContents;
    QHBoxLayout *horizontalLayout_2;
    QVBoxLayout *verticalLayout;
    QPushButton *pushButton;
    QPushButton *pushButton_2;
    QMenuBar *menuBar;
    QToolBar *mainToolBar;
    QStatusBar *statusBar;

    void setupUi(QMainWindow *MainWindow)
    {
        if (MainWindow->objectName().isEmpty())
            MainWindow->setObjectName(QStringLiteral("MainWindow"));
        MainWindow->resize(600, 396);
        centralWidget = new QWidget(MainWindow);
        centralWidget->setObjectName(QStringLiteral("centralWidget"));
        verticalLayout_2 = new QVBoxLayout(centralWidget);
        verticalLayout_2->setSpacing(6);
        verticalLayout_2->setContentsMargins(11, 11, 11, 11);
        verticalLayout_2->setObjectName(QStringLiteral("verticalLayout_2"));
        scrollArea = new QScrollArea(centralWidget);
        scrollArea->setObjectName(QStringLiteral("scrollArea"));
        scrollArea->setWidgetResizable(true);
        scrollAreaWidgetContents = new QWidget();
        scrollAreaWidgetContents->setObjectName(QStringLiteral("scrollAreaWidgetContents"));
        scrollAreaWidgetContents->setGeometry(QRect(0, 0, 574, 246));
        horizontalLayout_2 = new QHBoxLayout(scrollAreaWidgetContents);
        horizontalLayout_2->setSpacing(6);
        horizontalLayout_2->setContentsMargins(11, 11, 11, 11);
        horizontalLayout_2->setObjectName(QStringLiteral("horizontalLayout_2"));
        verticalLayout = new QVBoxLayout();
        verticalLayout->setSpacing(6);
        verticalLayout->setObjectName(QStringLiteral("verticalLayout"));

        horizontalLayout_2->addLayout(verticalLayout);

        scrollArea->setWidget(scrollAreaWidgetContents);

        verticalLayout_2->addWidget(scrollArea);

        pushButton = new QPushButton(centralWidget);
        pushButton->setObjectName(QStringLiteral("pushButton"));

        verticalLayout_2->addWidget(pushButton);

        pushButton_2 = new QPushButton(centralWidget);
        pushButton_2->setObjectName(QStringLiteral("pushButton_2"));

        verticalLayout_2->addWidget(pushButton_2);

        MainWindow->setCentralWidget(centralWidget);
        menuBar = new QMenuBar(MainWindow);
        menuBar->setObjectName(QStringLiteral("menuBar"));
        menuBar->setGeometry(QRect(0, 0, 600, 22));
        MainWindow->setMenuBar(menuBar);
        mainToolBar = new QToolBar(MainWindow);
        mainToolBar->setObjectName(QStringLiteral("mainToolBar"));
        MainWindow->addToolBar(Qt::TopToolBarArea, mainToolBar);
        statusBar = new QStatusBar(MainWindow);
        statusBar->setObjectName(QStringLiteral("statusBar"));
        MainWindow->setStatusBar(statusBar);

        retranslateUi(MainWindow);

        QMetaObject::connectSlotsByName(MainWindow);
    } // setupUi

    void retranslateUi(QMainWindow *MainWindow)
    {
        MainWindow->setWindowTitle(QApplication::translate("MainWindow", "MainWindow", 0));
        pushButton->setText(QApplication::translate("MainWindow", "add one", 0));
        pushButton_2->setText(QApplication::translate("MainWindow", "remove one", 0));
    } // retranslateUi

};

namespace Ui {
    class MainWindow: public Ui_MainWindow {};
} // namespace Ui

QT_END_NAMESPACE

#endif // UI_MAINWINDOW_H

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private slots:
    void on_pushButton_clicked();

    void on_pushButton_2_clicked();

private:
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QLabel>
#include <QDebug>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_pushButton_clicked()
{
    ui->verticalLayout->addWidget(new QLabel("This is a label", this));
    qDebug() << "Labels count: " << ui->verticalLayout->count();
}

void MainWindow::on_pushButton_2_clicked()
{
    delete ui->verticalLayout->takeAt(0);
    qDebug() << "Labels count: " << ui->verticalLayout->count();
}

的main.cpp

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

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

    return a.exec();
}

Answer 1

似乎我还必须删除QLayoutItem和Widget，只是删除小部件或QLayoutItem（我尝试过）不起作用，两者都必须删除，如下所示：

    QLayoutItem *child = ui->verticalLayout->takeAt(0);
    if (child)
    {
         delete child->widget();
         delete child;
    }