- Qt5 Tutorial: QTcpSocket with Signals and Slots. In this tutorial, we will learn how to download a file using QTcpSocket.This is a continued tutorial from the previous one, Qt 5 QTcpSocket.We're going to use Signal and Slot mechanism instead of calling functions manually(?).
- Nonetheless, the components need to communicate with each other and you need some kind of callback-mechanism. And this, ladies and gentlemen, this is where Qt's signals and slots comes to the rescue. This is the third post in the series 'Crash course in Qt for C developers' covering the signals and slots mechanism. The other topics are listed.
A method will only be registered with the meta-object system if it is a slot, a signal, or declared with the QINVOKABLE macro. Constructors can also be registered with QINVOKABLE. See also QMetaObject, QMetaEnum, QMetaProperty, and Qt's Property System.
Qt5 Tutorial QTcpSocket with Signals and Slots - 2018
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In this tutorial, we will learn how to download a file using QTcpSocket. This is a continued tutorial from the previous one, Qt 5 QTcpSocket. We're going to use Signal and Slot mechanism instead of calling functions manually(?).
Note: Qt5 document
The QTcpSocket class provides a TCP socket.
TCP (Transmission Control Protocol) is a reliable, stream-oriented, connection-oriented transport protocol. It is especially well suited for continuous transmission of data.
QTcpSocket is a convenience subclass of QAbstractSocket that allows you to establish a TCP connection and transfer streams of data. See the QAbstractSocket documentation for details.
For TCP Socket in general, please visit my C++ Tutorials: Socket - Server and Client.
We'll start with Qt Console Application.
First, we need to add network module to our project file, QTcpSocket.pro:
Then, we want to create a new class called MyTcpSocket.
Let's do work on main.cpp.
We need to create an instance of MyTcpSocket, and then call a our key driver function call, doConnect():
Now, let's implement the doConnect() method. But before doing that we should write some lines of code in the mytcpsocket.h:
- #include <QTcpSocket>
- the prototype of the method, doConnect()
- Socket object (pointer)
Once header file is done, let's move on to implementation file, mytcpsocket.cpp:
The void QAbstractSocket::connectToHost(const QString & hostName, quint16 port, OpenMode openMode = ReadWrite, NetworkLayerProtocol protocol = AnyIPProtocol) function attempts to make a connection to hostName on the given port. The protocol parameter can be used to specify which network protocol to use (eg. IPv4 or IPv6).
The socket is opened in the given openMode and first enters HostLookupState, then performs a host name lookup of hostName. If the lookup succeeds, hostFound() is emitted and QAbstractSocket enters ConnectingState. It then attempts to connect to the address or addresses returned by the lookup. Finally, if a connection is established, QAbstractSocket enters ConnectedState and emits connected().
At any point, the socket can emit error() to signal that an error occurred.
The hostName may be an IP address in string form (e.g., '43.195.83.32'), or it may be a host name (e.g., 'example.com'). QAbstractSocket will do a lookup only if required. port is in native byte order.
The bool QAbstractSocket::waitForConnected(int msecs = 30000) waits until the socket is connected, up to msecs milliseconds. If the connection has been established, this function returns true; otherwise it returns false. In the case where it returns false, we can call error() to determine the cause of the error.
For buffered devices, the bool QIODevice::waitForBytesWritten(int msecs) function waits until a payload of buffered written data has been written to the device and the bytesWritten() signal has been emitted, or until msecs milliseconds have passed. If msecs is -1, this function will not time out. For unbuffered devices, it returns immediately.
It returns true if a payload of data was written to the device; otherwise returns false (i.e. if the operation timed out, or if an error occurred).
This function can operate without an event loop. It is useful when writing non-GUI applications and when performing I/O operations in a non-GUI thread.
The bool QAbstractSocket::waitForReadyRead(int msecs = 30000) is reimplemented from QIODevice::waitForReadyRead().
This function blocks until new data is available for reading and the readyRead() signal has been emitted. The function will timeout after msecs milliseconds; the default timeout is 30000 milliseconds.
The function returns true if the readyRead() signal is emitted and there is new data available for reading; otherwise it returns false (if an error occurred or the operation timed out).
Uptown aces casino online. The qint64 QAbstractSocket::bytesAvailable() const is reimplemented from QIODevice::bytesAvailable().
This function eturns the number of incoming bytes that are waiting to be read.
Qt Signal Slot Thread
The QByteArray QIODevice::readAll() reads all available data from the device, and returns it as a QByteArray.
Run the code, then we get:
Here are the files used in this tutorial.
We can get it from TcpSocket.zip.
main.cpp:
Qt Signals And Slots Tutorial
mytcpsocket.h:
mytcpsocket.cpp:
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Connecting overloaded signals and slots in Qt 5 (3)
I'm having trouble getting to grips with the new signal/slot syntax (using pointer to member function) in Qt 5, as described in New Signal Slot Syntax. I tried changing this:
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to this:
but I get an error when I try to compile it:
error: no matching function for call to
QObject::connect(QSpinBox*&, <unresolved overloaded function type>, QSlider*&, void (QAbstractSlider::*)(int))
I've tried with clang and gcc on Linux, both with
-std=c++11
.What am I doing wrong, and how can I fix it?
Actually, you can just wrap your slot with lambda and this:
will be look better. :