If you have used Alarms and Reminders in Wp7 Mango SDK, you will notice that reminders can be detected by having a separate page in the application. But unfortunately there is no such detection mechanism available for Alarms. By detection mechanism what I mean is that- the differentiation between the app launch due to alarm and manual launch. What if the developer wanted to do something after the alarm has occurred? how does he detect that? I had the same problem and I am going to share the work around here. Its not a perfect substitute and may not be valid for all cases.
Microsoft has made the detection mechanism for knowing whether an alarm has occurred- private.The variable called p_completed which shows the status cannot be accessed. So practically there is not much we can do.
Prerequisites:
- You should be familiar with WP7 app development
- You should know about alarms and reminders in WP mango. If you are not aware of it check out this link- code samples of WP7
So lets get started.
For the sake of demonstration I am going to first create an application that adds and alarm and also can detect the same. So I open a new project, select Silverlight for windows phone 7 and load the project. Then drag and drop a button into the designer area. And place the following code in the click event. This is for creating a new alarm
try
{
Alarm a = new Alarm("first");
a.BeginTime = DateTime.Now.AddSeconds(40);
ScheduledActionService.Add(a);
}
catch
{
ScheduledActionService.Remove("first");
/*assuming that alarm already exists exception occurs due to that */
Alarm a = new Alarm("first");a.BeginTime = DateTime.Now.AddSeconds(40);
ScheduledActionService.Add(a); }
I create an alarm object a with the alarm name as first. I set the begin time as 40 seconds from the current time. And I add it to the ScheduledActionService. I handle the exception that is caused if the alarm named first already exists by removing it first and then creating it again.
Now I am going to detect whether the alarm launch has occurred in the PhoneApplicationPage_Loaded a event handler of Main page. The code is as follows ::
try
{
ScheduledAction a1 = ScheduledActionService.Find("first");
if ((a1.IsEnabled == true) && (a1.IsScheduled == false))
{
MessageBox.Show("Alarm detected");
}
ScheduledActionService.Remove("first");
}
catch
{
}
Now launch the application click add alarm and then close the application. Wait for the alarm pop up. Tap the pop up and there you go. Get a message saying that alarm is created.
How it works:
First I have declared an object a1 of schedule action and I pull the alarm first and store it in a1. This is done using ScheduledActionService.Find("first"). There are two key aspects to this. For an alarm to have occurred and after that the application is launched then the alarm must have been enabled but its not scheduled. So I check the above condition & then display a message saying alarm is detected. Now why did I add the remove alarm command. I do this because the next time the user launches the application manually, the state of alarm would be same. As I said earlier this work around is not a perfect substitute but can help sometimes. So you need to again create the alarm for the next use.
Bottleneck :
This workaround doesn’t work perfectly if the user clicks dismiss and then launches the application manually. In this case the application will say alarm is detected though its not the case
You can download the source code from here.
