Exercise: Use SQLite asynchronously

Completed

The application works well, but if the database contains many rows, the UI can become unresponsive while the app performs database queries and other operations. In this exercise, you convert the application from the synchronous SQLite API to the asynchronous version. This way, your application is always responsive no matter how many queries you make to your database.

Create an Async connection

1. Open the PersonRepository.cs file in the People project.

2. Modify the Init method's definition to be async. Change the return type of the method to Task.

3. Change the conn property to a SQLiteAsyncConnection and update the code in the Init method that initializes the connection.

4. Replace the call to the synchronous CreateTable method with the asynchronous CreateTableAsync method.

   The completed code should look like this:

   private SQLiteAsyncConnection conn;
   
   private async Task Init()
   {
       if (conn != null)
           return;
   
       conn = new SQLiteAsyncConnection(_dbPath);
   
       await conn.CreateTableAsync<Person>();
   }
   

Insert an item into a table asynchronously

1. Modify the definition of the AddNewPerson method to be async. Change the return type of the method to Task.

2. Add the await keyword to the Init method call because Init is now an async method.

3. Update the AddNewPerson method to insert a new Person by using an asynchronous insert operation.

   The code should look like this:

   using System.Threading.Tasks;
   ...
   public async Task AddNewPerson(string name)
   {
      int result = 0;
      try
      {
         // Call Init()
         await Init();
   
         // basic validation to ensure a name was entered
         if (string.IsNullOrEmpty(name))
               throw new Exception("Valid name required");
   
         result = await conn.InsertAsync(new Person { Name = name });
   
         StatusMessage = string.Format("{0} record(s) added [Name: {1})", result, name);
      }
      catch (Exception ex)
      {
         StatusMessage = string.Format("Failed to add {0}. Error: {1}", name, ex.Message);
      }
   }
   

Get all items from a table asynchronously

1. Modify the GetAllPeople method definition. This method should be async and return a Task<List<Person>> object.

2. Add the await keyword to the Init method call.

3. Update the method to return the results by using an asynchronous call.

   The code should look like this:

   public async Task<List<Person>> GetAllPeople()
   {
      try
      {
         await Init();
         return await conn.Table<Person>().ToListAsync();
      }
      catch (Exception ex)
      {
         StatusMessage = string.Format("Failed to retrieve data. {0}", ex.Message);
      }
   
      return new List<Person>();
   }
   

4. Save the PersonRepository.cs file.

Test the asynchronous functionality

1. Expand MainPage.xaml in the Solution Explorer and open the MainPage.xaml.cs file.

2. Modify both of the button-click event handlers so that they use the asynchronous methods from the PersonRepository class. Make use of the async and await keywords:

     public async void OnNewButtonClicked(object sender, EventArgs args)
     {
        statusMessage.Text = "";
   
        await App.PersonRepo.AddNewPerson(newPerson.Text);
        statusMessage.Text = App.PersonRepo.StatusMessage;
     }
   
     public async void OnGetButtonClicked(object sender, EventArgs args)
     {
        statusMessage.Text = "";
   
        List<Person> people = await App.PersonRepo.GetAllPeople();
        peopleList.ItemsSource = people;
     }
   

3. Save the MainPage.xaml.cs file.

4. Build and run the program on Windows and Android, verifying that it still functions as before.