Question

对于我的GUI，我希望有两对按钮可以向上和向下滚动滚动条。第一组按钮应该在说scrollarea1上工作，第二组按钮应该在scrollarea2上工作。我放在scrollarea中的小部件称为viewport1和viewport2。由于两组按钮都应该相同（向上和向下滚动），我想我会创建两个名为scrollUp和scrollDown的插槽来处理两组按钮的滚动。不幸的是，我无法完成这项工作，需要一些帮助。我尝试过以下方法：

QPushButton up;
QPushButton down;
QPushButton up2;
QPushButton down2;

connect(&up,SIGNAL(clicked()),&up,SLOT(scrollUp()));
connect(&up2,SIGNAL(clicked()),&up,SLOT(scrollUp()));
connect(&down,SIGNAL(clicked()),&down,SLOT(scrollDown()));
connect(&down2,SIGNAL(clicked()),&down,SLOT(scrollDown()));

void MainWindow::scrollDown()
{
QScrollArea area;
QWidget view;

if((QPushButton) &sender = down)
{
    area=scrollArea;
    view=viewport;
}
if((QPushButton) &sender = down2)
{
    area=scrollArea;
    view=viewport;
}
int curpos = area.verticalScrollBar()->value();
area.verticalScrollBar()->setValue(curpos+15);
int newpos = area.verticalScrollBar()->value();
QPoint topLeft = area.viewport()->rect().topLeft();
view.move(topLeft.x(),topLeft.y()-(newpos));
}

void MainWindow::scrollUp()
{
QScrollArea area;
QWidget view;

if((QPushButton) &sender = up)
{
    area=scrollArea;
    view=viewport;
}
if((QPushButton) &sender = up2)
{
    area=scrollArea2;
    view=viewport2;
}
int curpos = area.verticalScrollBar()->value();
area.verticalScrollBar()->setValue(curpos-15);
int newpos = area.verticalScrollBar()->value();
QPoint topLeft = area.viewport()->rect().topLeft();
view.move(topLeft.x(),topLeft.y()-(newpos));
}

但这不起作用有几个原因。我也尝试给插槽一些参数，例如：

connect(&up,SIGNAL(clicked()),&up,SLOT(scrollUp(scrollarea1,viewport1)));
connect(&up2,SIGNAL(clicked()),&up,SLOT(scrollUp(scrollarea2,viewport2)));

但同样，没有成功。有人能帮助我吗？

Answer 1

首先，“它不起作用”并不意味着什么，如果你没有说出你得到的错误，很难帮助你。然后，几乎没有问题。

所有QObject的派生类都不可复制，这意味着你无法做到

QWidget a;
QWidget b;
b = a; // Wrong

你应该使用指针（或者可能是引用）。

QWidget a;
QWidget * b = new QWidget(...);
QWidget * c;
c = & a; // Ok
c = b; // Ok

然后您的connect来电错误：

connect(&up, SIGNAL(clicked()), &up, SLOT(scrollUp()));

第三个参数是拥有插槽的对象。 up是一个QPushButton，它没有scrollUp()个广告位，是你的MainWindow做的：

connect(&up, SIGNAL(clicked()), this, SLOT(scrollUp()));

（因为在MainWindow的构造函数connect中调用this指向当前的MainWindow对象。）

同样在C ++中，单=符号表示赋值，对于相等比较，使用=='. And sender`是一个函数。

如果以正确的方式实施，您的方法应该有效：

class MainWindow: public QWidget
{
    QScrollArea * scroll1;
    QScrollArea * scroll2;
    QWidget * view1;
    QWidget * view2;
    QPushButton * up1;
    QPushButton * up2;
    QPushButton * down1;
    QPushButton * down2;

public:
    MainWindow()
    {
        // Here initialize member variables.
        ...

        connect(up1, SIGNAL(clicked()), this, SLOT(scrollUp()));
        connect(up2, SIGNAL(clicked()), this, SLOT(scrollUp()));
        connect(down1, SIGNAL(clicked()), this, SLOT(scrollDown()));
        connect(down2, SIGNAL(clicked()), this, SLOT(scrollDown()));
    }

public slots:
    void scrollDown()
    {
        QScrollArea * area;
        QWidget * view;

        if(qobject_cast<QPushButton>(sender()) == down1) {
            area = & scroll1;
            view = & view1;
        } else if(qobject_cast<QPushButton>(sender()) == down2) {
            area = & scroll2;
            view = & view2;
        } else {
            // Error.
        }

        // Now `area` and `view` point to the right widgets.
        ...
    }

    void scrollUp()
    {
        // The same as before.
    }
};

另一种方法是将实际滚动指令提取到单独的函数中：

class MainWindow: public QWidget
{
    // Same variables as before
    ...

public:
    MainWindow()
    {
        // Here initialize member variables.
        ...

        connect(up1, SIGNAL(clicked()), this, SLOT(scrollUp1()));
        connect(up2, SIGNAL(clicked()), this, SLOT(scrollUp2()));
        connect(down1, SIGNAL(clicked()), this, SLOT(scrollDown1()));
        connect(down2, SIGNAL(clicked()), this, SLOT(scrollDown2()));
    }

public slots:
    void scrollDown(QScrollArea * area, QWidget * view)
    {
        // Here you scroll over `area` and `view`.
    }

    void scrollDown1()
    {
        scrollDown(scroll1, area1);
    }

    void scrollDown2()
    {
        scrollDown(scroll2, area2);
    }

    // Again, the same for `scrollUp`.
};

Answer 2

您的代码中存在多个错误：

关于信号的发件人：没有名为“QObject”的sender，而是方法QObject * QObject::sender() const;，它会在信号的发送方返回一个指针。
在if条件中：您将QPushButton**投射到QPushButton（(QPushButton) &sender）中，并且您不会将该事物与按钮up(2)和{{1}进行比较}。
在广告位和信号之间的连接中：down(2)和scrollUp广告位不属于scrollDown类，而属于QPushButton类。

最后，你应该写下这样的东西：

MainWindow

Answer 3

首先，插槽除了信号之外没有其他参数。 Clicked没有参数，因此插槽没有参数。

我认为检查scrollArea 1或2是否具有焦点并决定哪一个应该移动的最简单方法。

我还认为您的代码中存在错误。不应该这样：

if((QPushButton) &sender = down2)
{
    area=scrollArea;
    view=viewport;
}

是这样的：

if((QPushButton) &sender = down2)
{
    area=scrollArea2;
    view=viewport2;
}

Answer 4

首先，这是伪代码。它不会编译，但它应包含必要的信息。

我相信使用QSignalMapper类可以最优雅地解决这个问题。它允许来自多个发送器的无参数信号连接到一个插槽。

在标题中，写下这样的内容：

class QSignalMapper;

class MainWindow : public QMainWindow
{

public:
  void init();

public slots:
  void handleScrollButtons(int id);

private:
enum { ScrollUp1, ScrollDown1, ScrollUp2, ScrollDown2 } // just makes it more convenient to use

QSignalMapper *m_scrollbuttonhandler;
}

在源文件中，写下这样的内容

#include <QSignalMapper>

void MainWindow::init()
{
  m_scrollbuttonhandler = new QSignalMapper(this);
  m_scrollbuttonhandler->setMapping(scrollup1button, ScrollUp1);
  m_scrollbuttonhandler->setMapping(scrolldown1button, ScrollDown1);
  m_scrollbuttonhandler->setMapping(scrollup2button, ScrollUp2);
  m_scrollbuttonhandler->setMapping(scrolldown2button, ScrollDown2);
  connect(scrollup1button, SIGNAL(clicked(bool)), m_scrollbuttonhandler, SLOT(map()));
  connect(scrolldown1button, SIGNAL(clicked(bool)), m_scrollbuttonhandler, SLOT(map()));
  connect(scrollup2button, SIGNAL(clicked(bool)), m_scrollbuttonhandler, SLOT(map()));
  connect(scrolldown2button, SIGNAL(clicked(bool)), m_scrollbuttonhandler, SLOT(map()));

  connect(m_scrollbuttonhandler, SIGNAL(mapped(int)), this, SLOT(handleScrollButtons(int)));
}

void MainWindow::handleScrollButtons(int id)
{
  switch (id)
  {
    case ScrollUp1:
    // stuff to do for scrollup1button
    case ScrollDown1:
    // stuff to do for scrolldown1button
    case ScrollUp2:
    // stuff to do for scrollup2button
    case ScrollDown2:
    // stuff to do for scrolldown2button
  }
}

一个插槽的多个信号

4 个答案: