Qt - “没有这样的槽”，虽然有 [英] Qt - "No such slot", although there is

问题描述

我试图将一个按钮连接到一个函数，所以当我按下按钮，该函数被调用具体的参数。我有

  class FieldGridWidget：public QWidget 
 {
 Q_OBJECT 
 
 public ：
 FieldGridWidget（QWidget * parent = 0）; 
〜FieldGridWidget（）; 
 
 public slots：
 void resizeGrid（int n）; 
 
 private：
 QGridLayout * _gridLayout; 
 QVector< QPushButton *> _buttonGrid; 
 
}; 
  

然后按钮

  _button3 = new QPushButton（3x3，this）; 
  

我试图连接它，所以如果点击， resizeGrid connect（_button3，SIGNAL）。$ {code} （clicked（）），_fieldGrid，SLOT（resizeGrid（3）））; //这是第21行

但我得到运行时错误
QObject :: connect：没有这样的插槽FieldGridWidget :: resizeGrid（3）in ../ filename.cpp：21

做错了？或者我怎么能这样，如果我按下按钮， resizeGrid（3）被调用？
谢谢！

解决方案

您不能将值直接传递到Qt中的插槽，如 SLOT（resizeGrid（3））。 SLOT 的参数应该只是您的方法的签名（ resizeGrid（））。

有两种方法可以将参数添加到插槽。关于如何将参数传递到广告位的问题显示了一些解决方案，此处重复。 （Go upvote them！）

现代的方式：Qt5和C ++ 11

插槽，连接到函子，如 Kuba Ober 在此回答：

  connect（action1，& QAction :: triggered， this，[this] {onStepIncreased（1）;}）; 
 connect（action5，& QAction :: triggered，this，[this] {onStepIncreased（5）;}）; 
 connect（action10，& QAction :: triggered，this，[this] {onStepIncreased（10）;}）; 
 connect（action25，& QAction :: triggered，this，[this] {onStepIncreased（25）;}）; 
 connect（action50，& QAction :: triggered，this，[this] {onStepIncreased（50）;}）; 
  

旧版：QSignalMapper

使用 QSignalMapper 按照 TonyK 在这个回答：

  QSignalMapper * signalMapper = new QSignalMapper 
 connect（action1，SIGNAL（triggered（）），signalMapper，SLOT（map（）））; 
 connect（action5，SIGNAL（triggered（）），signalMapper，SLOT（map（）））; 
 connect（action10，SIGNAL（triggered（）），signalMapper，SLOT（map（）））; 
 connect（action25，SIGNAL（triggered（）），signalMapper，SLOT（map（）））; 
 connect（action50，SIGNAL（triggered（）），signalMapper，SLOT（map（）））; 
 
 signalMapper  - > setMapping（action1，1）; 
 signalMapper  - > setMapping（actions5，5）; 
 signalMapper  - > setMapping（action10，10）; 
 signalMapper  - > setMapping（action25，25）; 
 signalMapper  - > setMapping（action50，50）; 
 
 connect（signalMapper，SIGNAL（mapped（int）），this，SLOT（resizeGrid（int）））; 
  

I'm trying to connect a button to a function, so when I push the button, the function gets called with a specific parameter. I have

class FieldGridWidget : public QWidget
{
    Q_OBJECT

public:
    FieldGridWidget(QWidget *parent=0);
    ~FieldGridWidget();

public slots:
    void resizeGrid(int n);

private:
    QGridLayout* _gridLayout;
    QVector<QPushButton*> _buttonGrid;

};

then the button

_button3 = new QPushButton("3x3", this);

and I'm trying to connect it so if clicked, the resizeGrid function gets called with the parameter 3. For this, I'm trying

connect(_button3, SIGNAL(clicked()), _fieldGrid, SLOT(resizeGrid(3))); //this is line 21

but I get the runtime error QObject::connect: No such slot FieldGridWidget::resizeGrid(3) in ../filename.cpp:21

What am I doing wrong? Or how can I make it so if I press the button, resizeGrid(3) gets called? Thank you!

解决方案

You cannot pass a value to a slot in Qt directly, as in SLOT(resizeGrid(3)). The argument to SLOT should be just the signature of your method (resizeGrid()).

There are two ways how to add an argument to a slot. This question about how to pass arguments to a slot shows some solutions, repeated here. (Go upvote them!)

The modern way : Qt5 and C++11

Instead of connecting a slot, connect to functor, as described by Kuba Ober in this answer:

connect(action1,  &QAction::triggered, this, [this]{ onStepIncreased(1); });
connect(action5,  &QAction::triggered, this, [this]{ onStepIncreased(5); });
connect(action10, &QAction::triggered, this, [this]{ onStepIncreased(10); });
connect(action25, &QAction::triggered, this, [this]{ onStepIncreased(25); });
connect(action50, &QAction::triggered, this, [this]{ onStepIncreased(50); });

Old fashioned : QSignalMapper

You can use a QSignalMapper to perform what you want, as described by TonyK in this answer:

QSignalMapper* signalMapper = new QSignalMapper (this) ;
connect (action1, SIGNAL(triggered()), signalMapper, SLOT(map())) ;
connect (action5, SIGNAL(triggered()), signalMapper, SLOT(map())) ;
connect (action10, SIGNAL(triggered()), signalMapper, SLOT(map())) ;
connect (action25, SIGNAL(triggered()), signalMapper, SLOT(map())) ;
connect (action50, SIGNAL(triggered()), signalMapper, SLOT(map())) ;

signalMapper -> setMapping (action1, 1) ;
signalMapper -> setMapping (action5, 5) ;
signalMapper -> setMapping (action10, 10) ;
signalMapper -> setMapping (action25, 25) ;
signalMapper -> setMapping (action50, 50) ;

connect (signalMapper, SIGNAL(mapped(int)), this, SLOT(resizeGrid(int))) ;

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