Sample App Notifications
,The Stock Quoter app uses all three types of push notifications, which are described in the following sections.
Tile Notifications
Tile notifications are sent periodically from the StockQuoteService and are displayed as shown in Figure 15.7. The tile notification contains a Text1 data property equal to Stock Quote and a Text2 data property that is the result of calling the ToString method of the StockQuote object, which produces a combination of the stock symbol, the stock’s last price, and its change in price.
Toast Notifications
Toast notifications are sent periodically from the StockQuoteService and are displayed as shown in Figure 15.4. The sample uses the title property of the tile notification to display the stock symbol, its price, and its change in price for the day. The count property is populated with an incrementing value, which is just for demonstration purposes.
Sample Background Images
For tile and raw notifications, the sample makes use of three images: StockUp.png, StockNone.png, and StockDown.png, located in the PushNotification/Images directory of the WPUnleashed.Examples project.
The logic for determining the background image for a tile notification is located server-side, as this excerpt from the StockQuoteService shows:
string background;
if (stockQuote.ChangeInPrice > 0)
{
background = "PushNotification/Images/StockUp.png";
}
else if (stockQuote.ChangeInPrice < 0)
{
background = "PushNotification/Images/StockDown.png";
}
else
{
background = "PushNotification/Images/StockNone.png";
}
Image paths are relative to the application project.
Raw Notifications
Raw notifications make use of the serialized StockQuote instance, as the following excerpt from the StockQuoteService class shows:
notifier.SendRawNotification(
stockQuote, subscriptionUrl, PushNotificationPriority.RealTime);
The StockQuote instance is serialized to a byte array, which is then used as the content for the raw notification. For more information on the serialization process, see the previous section “Receiving a Raw Notification.”
When a raw notification is received by the phone app and the StockQuote object is rehydrated in the PushNotificationViewModel class, the object is assigned to the viewmodel’s StockQuote property.
The view displays the stock information via the viewmodel’s StockQuote property, as shown in the following excerpt from the PushNotificationView.xaml file (style attributes have been removed for clarity):
<TextBlock Text="Price:" />
<TextBlock Text="{Binding StockQuote.LastPrice}" />
<TextBlock Text="Change:" />
<TextBlock Text="{Binding StockQuote.ChangeInPrice}" />
The stock direction image is presented using the viewmodel’s StockPriceDirection property. When the StockQuote changes in the viewmodel, the StockPriceDirection property is reevaluated and a different image displayed in the view. The following excerpt shows the StockQuote property in the viewmodel:
StockQuote stockQuote;
public StockQuote StockQuote
{
get
{
return stockQuote;
}
set
{
Assign(ref stockQuote, value);
/* Set the direction so that the view
* doesn't need to do any evaluation. */
if (stockQuote == null || stockQuote.ChangeInPrice == 0)
{
StockPriceDirection = StockPriceDirection.None;
}
else if (stockQuote.ChangeInPrice > 0)
{
StockPriceDirection = StockPriceDirection.Up;
}
else
{
StockPriceDirection = StockPriceDirection.Down;
}
}
}
The view itself subscribes to the viewmodel’s PropertyChanged event. When the StockPriceDirection property changes, it determines what image should be displayed, depending on its value.
void viewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == "StockPriceDirection")
{
string url;
switch (ViewModel.StockPriceDirection)
{
case StockPriceDirection.Down:
url = "Images/StockDown.png";
break;
case StockPriceDirection.Up:
url = "Images/StockUp.png";
break;
default:
url = "Images/StockNone.png";
break;
}
Image_StockQuote.Source = new BitmapImage(
new Uri(url, UriKind.Relative));
}
}
Updating the UI based on a viewmodel property could be better orchestrated using the page’s VisualStateManager. In Chapter 18, “Incorporating Map-Based Positioning,” we discuss a custom VisualStateUtility class that allows you to bind the visual state of a UI element to a viewmodel property.
Opting Out of Stock Price Updates
The Stock Quoter application allows a user to unregister from receiving stock updates. By clicking the Unregister button, the viewmodel’s UnregisterPushNotification method is called, which calls the PushNotificationSubscriber object’s Unsubscribe method, as shown:
public void UnregisterForPushNotification()
{
try
{
Message = "Unregistering for notifications.";
if (subscriber != null)
{
subscriber.Unsubscribe();
subscriber.Dispose();
subscriber = null;
}
Message = "Unregistered for notifications.";
}
catch (Exception ex)
{
Message = "Problem unregistering: " + ex.ToString();
}
if (channelUri != null)
{
try
{
UnregisterWithServer(channelUri.ToString());
}
catch (Exception ex)
{
Message = "Problem unregistering with server: " + ex.ToString();
}
}
}
When the PushNotificationSubscriber is disposed, its Timer and HttpNotificationChannel are also disposed. The cloud service is then notified that push notifications should no longer be sent.