Consult with Qt signals and slots-CodePudding

In the MainWindow defines a myPushButton pointer,

 
The class MainWindow: public QMainWindow 
{
Q_OBJECT 

Public: 
MainWindow (QWidget * parent=nullptr); 
~ MainWindow (); 
Void guanbi (); 

Private: 
Ui: : MainWindow * Ui; 
MyPushButton * nBtn;//& lt; -- -- -- 
};

This is the definition of myPushButton

 
The class myPushButton: public QPushButton 
{
Q_OBJECT 
Public: 
Explicit myPushButton (QWidget * parent=nullptr); 
~ myPushButton (); 
Void response (); 
Signals: 
Void mys ();//& lt; The launch of the signal 
 -}; 

Void myPushButton: : response () 
{
QDebug () & lt; & lt;" The response to myclicked!" ; 
}

Then the same signal mys,

 
MainWindow: : MainWindow (QWidget * parent) 
: QMainWindow (parent) 
, the UI (new UI: : MainWindow) 
{
The UI - & gt; SetupUi (this); 
NBtn=new myPushButton; 
NBtn - & gt; Move (100200); 
NBtn - & gt; The resize (50, 100); 
NBtn - & gt; NPushbutton setText (" "); 
NBtn - & gt; SetParent (this); 
SetWindowTitle (" test window "); 
SetFixedSize (800600); 

The connect (nBtn, & amp; MyPushButton: : mys, this, & amp; MainWindow: : close);//& lt; Function - associated signals and slots, 
Guanbi ();//& lt; - transmitting 
} 

MainWindow: : ~ MainWindow () 
{
QDebug () & lt; & lt;" MainWindow 's destructor!" ; 
Delete the UI; 
} 

Void MainWindow: : guanbi () 
{
QDebug () & lt; & lt;" Emit signal!" ; 
Emit nBtn - & gt; Mys (); 

}

According to the print run, emission signal is normal, but the MainWindow cannot shut (namely MainWindow always displayed after running, not closed), if to replace the connect function with the following way, the response function can run normally, suggesting that connect the signal there is no problem, but why can't perform the close?
The connect (nBtn, & amp; MyPushButton: : mys, nBtn, & amp; MyPushButton: : response);

Consult everybody, thank you!

CodePudding user response:

Perform guanbi (), the MainWindow haven't into the event loop (in the constructor of MainWindow)

CodePudding user response:

reference 1/f, non Yi response:

perform guanbi (), the MainWindow haven't into the event loop (in the constructor of MainWindow)

Why connection to connect (nBtn, & amp; MyPushButton: : mys, nBtn, & amp; MyPushButton: : response), the response can normal execution, not still in the constructor of MainWindow, nor enter the event loop?
I am a novice, is not very good, thank you.

CodePudding user response:

The connect function prototypes for:

 QMetaObject: : Connection QObject: : connect (const QObject * sender, 
Const char * signal, 
Const QObject * receiver, 
Const char * method, 
Qt: : ConnectionType type=Qt: : AutoConnection);

The last parameter decision, the signal channel is directly connected or queue connection, the default value is Qt: : AutoConnection
For Qt: : AutoConnection:
1, the sender and receiver attached thread is the same, is a direct connection
2, the sender and receiver attached thread is not the same, is a queue connection

Attached thread can be understood as: in which thread new attachment which thread, eg:

 A * A=new A;//a clinging thread for thread1 
Thread2 QThread *=new QThread; 
A - & gt; MoveToThread (thread2);//a thread itself into thread2

Direct connection: similar to directly call a function (immediately)
The signal is placed in a queue queue connection:, receiver, such as free start

 connect (nBtn, 
& MyPushButton: : mys, 
NBtn, 
& MyPushButton: : response);

Is a direct connection, myPushButton: : mys signal launch, will immediately perform myPushButton: : response

 connect (nBtn, 
& MyPushButton: : mys, 
This, 
& MainWindow: : close);

Is also a direct connection, myPushButton: : mys signal launch, will immediately perform MainWindow: : close

But in the MainWindow: : close, not just close the window, but send a QCloseEvent event to the MainWindow
QCloseEvent will distribute in the event loop MainWindow, to filter the events in the event distribution (these are another story)

 QApplication a (arg c, argv); 
. 

//event loop 
//before the event loop to invoke the close invalid 
A.e xec ();

CodePudding user response:

references 4 floor of Yi reply:

connect function prototypes for:
 QMetaObject: : Connection QObject: : connect (const QObject * sender, 
Const char * signal, 
Const QObject * receiver, 
Const char * method, 
Qt: : ConnectionType type=Qt: : AutoConnection); 
The last parameter decision, the signal channel is directly connected or queue connection, the default value is Qt: : AutoConnection
For Qt: : AutoConnection:
1, the sender and receiver attached thread is the same, is a direct connection
2, the sender and receiver attached thread is not the same, is a queue connection

Attached thread can be understood as: in which thread new attachment which thread, eg:
 A * A=new A;//a clinging thread for thread1 
Thread2 QThread *=new QThread; 
A - & gt; MoveToThread (thread2);//a thread itself into thread2 
Direct connection: similar to directly call a function (immediately)
The signal is placed in a queue queue connection:, receiver, such as free start
 connect (nBtn, 
& MyPushButton: : mys, 
NBtn, 
& MyPushButton: : response); 
Is a direct connection, myPushButton: : mys signal launch, will immediately perform myPushButton: : response
 connect (nBtn, 
& MyPushButton: : mys, 
This, 
& MainWindow: : close); 
Is also a direct connection, myPushButton: : mys signal launch, will immediately perform MainWindow: : close

But in the MainWindow: : close, not just close the window, but send a QCloseEvent event to the MainWindow
QCloseEvent will distribute in the event loop MainWindow, to filter the events in the event distribution (these are another story)
 QApplication a (arg c, argv); 
. 

//event loop 
//before the event loop to invoke the close invalid 
A.e xec (); 

Thank you for your detailed answer, then ask next:
You answer the last mentioned above "in the MainWindow: : close, not just close this window, but send a QCloseEvent event to the MainWindow
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