ASP.NET Web PDF Document Viewer/Editor Control Library

In the previous example, you saw the floatingWindowBehavior and how you can use it to implement a pop-up menu. You can also use this behavior to implement true floating windows where you can drag and drop to rearrange information on your screen. You are probably familiar with this if you have used portals such as Live.com or Start.com that allow you to arrange the screen according to your preferences. In this example, you ll do exactly that. You ll have a page with a number of HTML panes in it that can be rearranged as you desire. This uses the <floatingBehavior> control to implement this functionality. This is the power of behaviors. You simply have to identify an element and add the behavior to it.

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Our ToDoEntry class doesn t offer change notification events, so we had to tell the binding source that it needs to refresh any controls bound to the current item by calling ResetCurrentItem. If we implemented INotifyPropertyChanged on ToDoEntry so that it raised an event anytime a property changed, this last line would be unnecessary. We need to add a call to this new method in our constructor so that we have one entry to start with:

public Form1() { InitializeComponent(); entriesSource.DataSource = entries; } CreateNewItem();

Working with the Mouse Wheel The mouse wheel is usually considered a part of the mouse, but the event has a separate event object. The object contains the position of the mouse pointer when the event occurs as well as the orientation of the wheel and the size of the scrolling (delta). The event handler is shown in Listing 6-15. The mouse wheel event is first sent to the widget under the mouse pointer. If it is not handled there, it is passed on to the widget with focus. Listing 6-15. The wheel is separate from the rest of the mouse. void EventWidget::wheelEvent( QWheelEvent * event ) { emit gotEvent( QString("wheelEvent( x:%1, y:%2, delta:%3, orientation:%4 )")

With this in place, we ll see the New entry title set by the CreateNewItem method appearing in the Title text box as Figure 22-10 shows. The description is empty for now, so there s nothing to see, and although the due date is now bound to the DueDate property, there s no obvious evidence of this DueDate is set to the current time and date, which is what the DateTimePicker control defaults to in the absence of any other information, so we can t see any change resulting from data binding for that control yet.

There s one glaring omission: the ListView isn t showing any data. And that s because, as mentioned previously, it doesn t have built-in support for data binding. We re going to need to write some code. Fortunately, it s relatively straightforward the binding source raises events to let us know whenever something has changed. If you select the entriesSource item in the form s design view and then go to the Properties panel and select the lightning bolt symbol to show the available events, there s a ListChanged event. We can add a handler by double-clicking that event. We expect three kinds of changes in the application addition of new items, updates to existing items, and deletion of existing items so we ll be writing three methods to handle that. The change event argument tells us which kind of change we re getting, so we just pick the relevant method based on the change type, as Example 22-3 shows.

private void entriesSource_ListChanged(object sender, ListChangedEventArgs e) { switch (e.ListChangedType) { case ListChangedType.ItemAdded: MakeListViewItemForNewEntry(e.NewIndex); break; case ListChangedType.ItemDeleted: RemoveListViewItem(e.NewIndex); break; case ListChangedType.ItemChanged: UpdateListViewItem(e.NewIndex); break;

}

.arg( event->x() ) .arg( event->y() ) .arg( event->delta() ).arg( event->orientation()==Qt::Horizontal "Horizontal":"Vertical" ) ); } There are more event handlers implemented in the EventWidget class. You can learn a lot about widgets by trying out different things on the widget and then studying the log.

}

You can see this example in action in Figure 5-21.

You might be wondering why we are asking the binding source to tell us when items have been added and changed, when we re writing the code that adds and changes items in the first place. The main reason is that there are certain tricky cases, such as what happens if you have an event handler for a text box s TextChanged event that runs as a result of a data-binding-related change, but which in turn causes further data binding changes; it s easy to tie yourself in knots, or end up with code that s rather fragile because it depends on things happening in a specific order. But if we just perform updates when the data binding system tells us to (via the events that BindingSource raises) things tend to run more smoothly. Let s start with the code that handles the addition of a new entry. We need to create a new ListViewItem for the list and ensure that it contains two columns. Since a new ListViewItem already has one column by default, we need to add a second one, as Example 22-4 shows. And then we just insert it into whatever position the binding source said it was added to in this application we always expect that to be the end, but since we re given a specific index, we may as well use it.