Access to a Parse service is through the Parse .NET SDK, and all connections to Parse are made over HTTPS with Parse rejecting non-HTTPS connections.

Instructions on setting up a Parse service can be found in the readme file that accompanies the sample application. When the sample application is run it will connect to a Parse service, as shown in the following screenshot:

Consuming a Parse Service

Xamarin.Forms applications identify themselves to Parse with an application ID and a .NET key, which are created when a new Parse backend application is created. The following code example shows how the sample application creates a connection to Parse:

protected ParseStorage ()
{
  ...
  ParseClient.Initialize (Constants.ApplicationId, Constants.Key);
}

The ParseClient.Initialize method is used to authenticate the sample application with the Parse backend application, and must be called before the sample application can use any Parse services.

Creating ParseObjects

The ParseObject class is used to store data on Parse. Each ParseObject contains key-value pairs of JSON-compatible data. The data does not use a schema, so it is not necessary to specify in advance the keys that exist on each ParseObject.

The sample application uses the TodoItem class to model data. In order to store a TodoItem instance on Parse, it must first be converted to a ParseObject instance. This is accomplished by the ToParseObject method, as shown in the following code example:

ParseObject ToParseObject (TodoItem todo)
{
  var po = new ParseObject ("TodoItem");
  if (todo.ID != string.Empty) {
    po.ObjectId = todo.ID;
  }
  po ["Title"] = todo.Name;
  po ["Description"] = todo.Notes;
  po ["IsDone"] = todo.Done;

  return po;
}

This method creates a new ParseObject, giving it a class name of "TodoItem." It then sets the ObjectID property of the ParseObject instance. The combination of a class name and an ObjectID uniquely identifies a ParseObject. Finally, the ParseObject instance is set with the rest of the data from the TodoItem instance.

Similarly, when data is retrieved from Parse, it must be converted from a ParseObject instance to a TodoItem instance. This is accomplished with the FromParseObject method, as shown in the following code example:

static TodoItem FromParseObject (ParseObject po)
{
  var t = new TodoItem ();
  t.ID = po.ObjectId;
  t.Name = Convert.ToString (po ["Title"]);
  t.Notes = Convert.ToString (po ["Description"]);
  t.Done = Convert.ToBoolean (po ["IsDone"]);
  return t;
}

This method simply retrieves the data from the ParseObject instance and sets it in the newly created TodoItem instance.

For more information about the ParseObject class, see The Parse Object on Parse's website.

Retrieving Data

The ParseQuery.FindAsync method is used to retrieve data from Parse, as shown in the following code example:

async public Task<List<TodoItem>> RefreshDataAsync ()
{
  var query = ParseObject.GetQuery("TodoItem");
  var results = await query.FindAsync ();

  var Items = new List<TodoItem> ();
  foreach (var item in results) {
    Items.Add (FromParseObject (item));
  }

  return Items;
}

A ParseQuery instance is created that will retrieve any ParseObject instances that have a class name of "TodoItem". An IEnumerable collection of matching ParseObject instances is then retrieved from Parse using the FindAsync method. The ParseObject collection is then converted to a List of TodoItem instances for display.

For more information about Parse queries, see Queries on Parse's website.

Creating and Updating Data

The ParseObject.SaveAsync method is used to save data to Parse, as shown in the following code example:

public async Task SaveTodoItemAsync (TodoItem todoItem)
{
  ...
  await ToParseObject (todoItem).SaveAsync ();
  ...
}

When using the SaveAsync method to update existing data stored on Parse, the Parse .NET SDK will automatically work out which data in the ParseObject has changed, so that only changed data is sent to Parse.

For more information about creating and updating data on Parse, see Saving Objects and Updating Objects on Parse's website.

Deleting Data

The ParseObject.DeleteAsync method is used to delete data on Parse, as shown in the following code example:

public async Task DeleteTodoItemAsync (TodoItem item)
{
  ...
  await ToParseObject (item).DeleteAsync ();
  ...
}

For more information about deleting data on Parse, see Deleting Objects on Parse's website.

Summary

This article examined how to consume a Parse web service from a Xamarin.Forms application, using the Parse .NET SDK. Parse provides backend solutions for mobile applications, eliminating the need for writing server code and maintaining servers.