Question

I’m trying to use a task launcher in WP7.1 Mango with the latest version of Caliburn Micro, but my code is not getting called back once the task has completed. Probably I’m doing something stupid somewhere, but I cannot see where. Here is what I did for a sample repro application you can download from:

http://www.filesonic.com/file/2750397005/PhoneTaskTest.zip

1) create a new WP7.1 application;

2) add a Lib folder in the solution, add there CM dll’s, and add a reference to them;

3) change the generated files as specified by CM documentation and add a bootstrapper.

Now up to this point everything is OK and the application starts with no issues. I then do the following for taking a photo:

4) add a button in the main page to the view and a corresponding method in its VM, named TakePhoto.

5) change the VM as follows:

a) add a readonly IEventAggregator member injected in the constructor;

b) add OnActivate/OnDeactivate overrides to let the aggregator subscribe and unsubscribe this VM;

c) add the TakePhoto method which is just:

_aggregator.RequestTask<CameraCaptureTask>();

d) derive the VM from interface IHandle<TaskCompleted<CameraCaptureTask>> and implement it:

public void Handle(TaskCompleted<CameraCaptureTask> message)
{
  if (message.Result.TaskEventArgs.TaskResult != TaskResult.OK) return;
  SetPhoto(message.Result.TaskEventArgs.ChosenPhoto);
}

Now, when I click the button the camera task starts in the emulator and I can take a photo; then I’m taken back to my application, but nothing happens and my Handle method is NEVER called. You can just place a breakpoint there to confirm this.
So, what I’m doing wrong here?

Answer 1

You need to handle TaskCompleted<PhotoResult> instead of TaskCompleted<CameraCaptureTask>. Because Caliburn.Micro creates theTaskCompleted<T> message with the event args of the Task’s Completed event which is in the case of CameraCaptureTask is PhotoResult. So you should implement IHandle<TaskCompleted<PhotoResult>> and your Handle method should look like this

public void Handle(TaskCompleted<PhotoResult> message)
{
    if (message.Result.TaskResult != TaskResult.OK) return;
    SetPhoto(message.Result.ChosenPhoto);
}