QFutureWatcher

-

 

QFutureWatcher

QFutureWatcher is useful in keeping track of when an asynchronous task complete. Consider a scenario where a dialog pops up while some operation runs in the background. The first step is to show the dialog:

  msgDialog = new MessageDialog();
  msgDialog->show();
  QApplication::processEvents(); //needed to properly show the dialog

Having a QFuture m_OperationFuture as a field, a naive approach to keeping the GUI responsive while the background operation takes place is to keep calling QApplication::processEvents() while the operation is still executing:

m_OperationFuture = QtConcurrent::run(runBackgroundOperation);
while(m_OperationFuture.isRunning())
{
       QApplication::processEvents();
}
performNextOperation();

However, QFutureWatcher provides a better alternative:

QFutureWatcher<QString> *watcher = new QFutureWatcher<QString>(this);
QObject::connect(watcher,SIGNAL(finished()),this,SLOT(operationFinished()));
m_OperationFuture = QtConcurrent::run(runBackgroundOperation);
watcher->setFuture(m_OperationFuture);

In the operationFinished() function, the result can be retrieved and the dialog can be closed:

QString err = m_OperationFuture.result();
closeDialog();

Comments

Post a Comment

Popular posts from this blog

QTreeView and QTableView dynamic changes

-
Image
Dynamically adding items to  QTreeView  and  QTableView Create the UI as follows, with the treeview on the left hand side and the table view on the right hand side. Notes The header file contains the models and the selection models for the tree view and the table view: QStandardItemModel * treeViewModel ; QItemSelectionModel * treeViewSelectionModel ; QItemSelectionModel * tableSelectionModel ; QStandardItemModel * tableModel ; In the .cpp file, the tree view models and table view models are set as the models for the selection models. treeViewSelectionModel -> setModel ( treeViewModel ) ; tableSelectionModel -> setModel ( tableModel ) ; The following code illustrates how to dynamically add a new row to the treeview. void MainWindow :: updateTreeView ( ) { QStandardItem * newRow = new QStandardItem ( QString ( "inserted row" ) ) ; QList < QStandardItem * > newRows ; newRows . append ( newRow ) ; auto f
Read more

C++ strings and string_view

-
C-style strings C style strings should be avoided except when interfacing with C libraries. C string library functions provide no bounds checking and memory allocation support. They are represented as an array of characters. Last character of the string is the null character  \0 , so that code that uses the string knows where it ends. The space needed for a string is always one more than the number of readable characters. String Literals Strings written with quotes around them are string literals. They are stored in a read-only part of memory. Because they are stored in readonly sections, attempting to modify string literals is  undefined behavior . Example: char * str = "world" ; str [ 0 ] = 'y' ; //undefined behavior If the code respected the standard and assigned the string literal to  const char* , the compiler will catch attempts to modify string literals: const char * str = "world" ; str [ 0 ] = 'k' ; //compiler will f
Read more