.NET/Java PDF, Tiff, Barcode SDK Library

Earlier, we configured a data source and then we added some controls to represent our data. Now it s time to connect the two. If we select the text box for the title, and then in the Properties panel scroll to the top of the list, there s an expandable (DataBindings) item, inside which is a list of properties you re likely to want to bind. (You can bind other properties, but most controls have only a handful of properties that it s likely to be useful to data-bind to.) If you show the drop down for the Text property, the reason for adding a binding source earlier becomes apparent. As Figure 22-9 shows, Visual Studio offers a list of available data sources (just the one here our form s entriesSource), which you can expand to select the property you require. We ll bind the two text boxes and date picker (binding the Value property in that case) on our form to the three properties. To check that this is working, we ll need some data the list we created earlier is currently empty. We ll add a helper function to create a new item; we ll need this for when the user clicks the New button, as well as for creating an initial item for when the application starts:

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private void CreateNewItem() { ToDoEntry newEntry = (ToDoEntry) entriesSource.AddNew(); newEntry.Title = "New entry";

The context menu event is triggered when the user tries to bring up a context menu (the menu that appears when right-clicking on something usually offering actions such as cut, copy, and paste). This event can be triggered with both the mouse and the keyboard. The event object contains the source of the request (reason) and the coordinates of the mouse pointer when the event occurs. The handler is shown in Listing 6-13. If a context menu event is ignored, it is reinterpreted and sent as a mouse event, if possible. All event objects carrying the mouse position have the pos() and globalPos() methods. The pos method is the position in widget-local coordinates, which is good for updating the widget itself. If you want to create a new widget at the location of the event, you need to use the global coordinates instead. The positions consist of x and y coordinates, which can be obtained directly from the event object through the x, y, globalX, and globalY methods. Listing 6-13. A context menu has been requested. void EventWidget::contextMenuEvent( QContextMenuEvent * event ) { emit gotEvent( QString("contextMenuEvent( x:%1, y:%2, reason:%3 )")

}

newEntry.DueDate = DateTime.Now; entriesSource.ResetCurrentItem();

Notice that we re using the AddNew method offered by the binding source this means the binding system is aware that a new item is being created, and if other controls end up being bound to the same source, they will be aware of the change. We then modify two of the properties.

.arg(event->x()) .arg(event->y()) .arg(event->reason()==QContextMenuEvent::Other "Other" : (event->reason()==QContextMenuEvent::Keyboard "Keyboard" : "Mouse")) ); } The context menu event carries the mouse position, as does the QMouseEvent. The mouse events are mousePressEvent, mouseReleaseEvent, mouseMoveEvent, and mouseDoubleClickEvent. You can see the latter in Listing 6-14. The handler shows the button as well as the x and y coordinates. When dealing with mouse events, it is important to understand that the movement event is sent only as long as a mouse button is pressed. If you need to get the movement event at all times, you must enable mouse tracking with the mouseTracking property. If you want to get all the mouse events, you can use the mouse just as you can use the keyboard. Use the methods grabMouse() and releaseMouse() for this. Just be careful because a bug occurring while the mouse is grabbed can prevent mouse interaction for all applications. The rule is to grab only when necessary, to release as soon as possible, and to never ever forget to release the mouse. Listing 6-14. A mouse event handling method void EventWidget::mouseDoubleClickEvent( QMouseEvent * event ) { emit gotEvent( QString("mouseDoubleClickEvent( x:%1, y:%2, button:%3 )") .arg( event->x() ) .arg( event->y() ) .arg( event->button()==Qt::LeftButton "LeftButton": event->button()==Qt::RightButton "RightButton": event->button()==Qt::MidButton "MidButton": event->button()==Qt::XButton1 "XButton1": "XButton2" ) ); }

Since we re using a BindingList, the data binding system would also be aware of a new item if we just added it directly to the entries collection. However, there s a subtle difference with AddNew rather than just appearing on the end of the list view, this new item will become the selected item. And in fact, it ll be in a tentative state until we move to a different item or add another new one this program happens not to exploit this, but we could cancel the addition of a new item if the user presses the Escape key.