Qt Documentation

When a parent is deleted all its children are deleted too. Sets the attribute code to have value value. When the HTTP protocol returns a redirect no error will be reported. In that case, if a larger column width is required by either the view's header or the item delegate, that width will be used instead. Use setModel to set the model.

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Also, we put up a QMessageBox with the info and a link to our log-file. You should expand according to your own needs. Google Breakpad could probably serve as a cross-platform substitute for that. Google Breakpad is a cross-platform application error reporting framework. Why doesn't Qt use exception handling?

That said, the answers from Crazy Eddie and Macke are pretty good, but don't always work. In particular, I found you can't use either of them from a slot function you've invoked from QML. So, I created a hacky work around for this problem. First, I created class derived from QException, which I'll skip over here, but is something you'll probably want to do. In this post, I just refer to it as "MyQException".

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service , privacy policy and cookie policy , and that your continued use of the website is subject to these policies. Can you show me an example of your try-catch there? I think I'm doing something wrong because I'm getting NO love from any try-catch I do except when I use the throw command myself.

And even then, the application still crashes and tries to send an error report to Apple in this case. This function is called whenever column 's size is changed in the header. Draws the branches in the tree view on the same row as the model item index , using the painter given.

The branches are drawn in the rectangle specified by rect. Draws the row in the tree view that contains the model item index , using the painter given. The option controls how the item is displayed. Draws the part of the tree intersecting the given region using the specified painter. See also collapseAll , expand , collapse , and setExpanded. See also expandAll , collapseAll , expand , collapse , and setExpanded.

This function should only be called after the model has been initialized, as the view needs to know the number of columns in order to hide column. See also showColumn and setColumnHidden. Note that the tree view uses the horizontal header section positions to determine the positions of columns in the view. See also hideColumn and isRowHidden. See also expand , expanded , and setExpanded. Returns true if the item in first column in the given row of the parent is spanning all the columns; otherwise returns false.

Returns true if the item in the given row of the parent is hidden; otherwise returns false. See also setRowHidden and isColumnHidden. Move the cursor in the way described by cursorAction , using the information provided by the button modifiers. Informs the view that the rows from the start row to the end row inclusive are about to removed from the given parent model item. Informs the view that the rows from the start row to the end row inclusive have been inserted into the parent model item.

Informs the view that the rows from the start row to the end row inclusive have been removed from the given parent model item. Scroll the contents of the tree view until the given model item index is visible. The hint parameter specifies more precisely where the item should be located after the operation.

If any of the parents of the model item are collapsed, they will be expanded to ensure that the model item is visible. See also columnWidth and resizeColumnToContents. Sets the item referred to by index to either collapse or expanded, depending on the value of expanded.

See also expanded , expand , and isExpanded. If span is true the item in the first column in the row with the given parent is set to span all columns, otherwise all items on the row are shown. If hide is true the row with the given parent is hidden, otherwise the row is shown.

See also isRowHidden and setColumnHidden. This specifies that the tree structure should be placed at logical index index. If set to -1 then the tree will always follow visual index 0. See also treePosition , QHeaderView:: See also hideColumn and setColumnHidden. If you need to set the width of a given column to a fixed value, call QHeaderView:: If you reimplement this function in a subclass, note that the value you return is only used when resizeColumnToContents is called.

In that case, if a larger column width is required by either the view's header or the item delegate, that width will be used instead. Note that not all models support this and may even crash in this case. Return the logical index the tree is set on. If the return value is -1 then the tree is placed on the visual index 0. Returns the rectangle on the viewport occupied by the item at index. If the index is not visible or explicitly hidden, the returned rectangle is invalid.

For better understanding, here follows and example. Example shows our example class. It is derived from QObject and reports everything that happens to it to the console. This will make it obvious what takes place when. To make something useful with the class, a main routine is required. It is shown in example Notice that the first thing that happens is that a QApplication instance is created. This is required for nearly all Qt applications and is good practice to avoid unnecessary problems.

The code creates a memory hierarchy shown in figure Make sure to understand how the tree is translated into the code from example and vice versa. Example shows an example run of the example code. As can be seen all objects are deleted, parents first and then chilren. Notice that each branch is deleted completely before the next is started upon.

This can be seen as z is deleted before y. If the parent reference is removed from x and y as shown in example , a memory leak occurs. This is as a test run documented in example The memory leak shown above does not do any harm in the current situation, as the application ends just after it has happended, but in another situation this could be a potential threat to the overall system stability.

The signals and slots are what makes the different Qt components as reuseable as they are. They provide a mechanism through which it is possible to expose interfaces that can be freely interconnected.

For example a menu item, push button, toolbar button and any other item can expose signal corresponding to "activated", "clicked" or any other appropriate event.

By connecting such a signal to a slot of any other item, the event automatically calls the slots. A signal can also include values, thus making it possible to connect a slider, a spinbox, a knob or any other value generating item to any item accepting values, for example another slider, knob or spinbox, or something completely different such as an LCD display. The key advantage of the signals and slots is that the caller does not have to know anything about the receiver and vice versa.

This makes it possible to integrate many components easily without the component's designer having actually thought about the used configuration. This is truly loose coupling. To make things a bit complicated, the development environment shipped with Qt 3. As they behave the same way is most cases this is not a problem, but throughout this text the term "slot" will be used. In order to be able to use the signals and slots each class has to be declared in a header file.

The implementation is best placed in a separate cpp file. The header file is then passed through a Qt tool known as the moc. The moc produces a cpp containing the code that makes the signals and slots happen and more. Figure illustrates this flow. This additional compilation stage may seem to complicate the building process, but there is yet another Qt tool, qmake.

This will be described in detail futher on in this tutorial. What are signals and slots - for real? The slots are then implemented as any class member method while the signals are implemented by the moc. Each object then holds a list of its connections which slots are activated by which signal and its slots which are used to build the connections table in the connect method. Of course there are more to this, but all can be seen by looking in a moc -generated cpp -file.

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