Exercise 1: Determine your database file path

In this exercise, you will create a new Xamarin.Forms application and determine the location to store a database file on each platform. We are going to initially display the full path to where we want to store the file as a Label as shown here:

To complete the exercise, you will need Visual Studio for Windows or macOS with the Xamarin development tools installed. You will also need either an emulator/simulator or a device to run the exercise on. Please see the setup page if you need help installing the Xamarin development environment.

Create the solution

We're going to start by creating a new Xamarin.Forms application using the Portable Class Library template.

Add platform-specific code

We'll add a new class to each platform specific project that will return a reasonable path that can be used to store a database file.

1. Add a new class named FileAccessHelper to each of the platform-specific projects. Ensure this class in each project is public.
2. Add a static method named GetLocalFilePath that accepts a string parameter named filename and returns a string. Make sure you add this method to each platform.

Note you can create the file in one project and then copy it into the other platform-specific projects to save some time and typing - just make sure to change the namespace and using statements to suite each platform.

public class FileAccessHelper
{
    public static string GetLocalFilePath(string filename)
    {

    }
}

3. Implement each of the GetLocalFilePath methods. The input parameter is the desired filename for the database. Return the combined folder location and database file name.
   • On Android, retrieve the Personal folder using the System.Environment.GetFolderPath method.

string path = System.Environment.GetFolderPath(
    System.Environment.SpecialFolder.Personal);
return System.IO.Path.Combine(path, filename);

4. On iOS, store the database in the Library folder. Again, start by retrieving the Personal folder using System.Environment.GetFolderPath. Then go up one folder level and navigate to Library. Hint: use System.IO.Path.Combine.

string docFolder = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
string libFolder = System.IO.Path.Combine(docFolder, "..", "Library");

if (!System.IO.Directory.Exists(libFolder)) {
    System.IO.Directory.CreateDirectory(libFolder);
}

return System.IO.Path.Combine(libFolder, filename);

5. For any of the supported Windows platforms, the folder location can be found using Windows.Storage.ApplicationData.Current.LocalFolder.Path.

string path = global::Windows.Storage.ApplicationData.Current.LocalFolder.Path;
return System.IO.Path.Combine(path, filename);

Display the path

We'll show the fully qualified path using the Label created by default with the Xamarin.Forms new project template. We need to make a few small changes to make this happen.

1. First, let's make the Label accessible to our code behind.
   • Open the MainPage.xaml file in the PCL project.
   • Locate the single Label child.
   • Add an x:Name attribute and name the label textLabel.
2. Next, open the C# MainPage code-behind class in the PCL project.
   • Add a new public property named Text and have the get/set operators retrieve and change the value of the textLabel.Text visual property.

public partial class MainPage : ContentPage
{
    public string Text
    {
        get { return textLabel.Text; }
        set { textLabel.Text = value; }
    }

    public MainPage()
    {
        InitializeComponent();
    }
}

3. Open the C# Application class in the PCL project.
   • Change the App constructor to accept a string parameter named displayText.
   • After the MainPage is created, set the Text property to the value passed into the constructor.

public App(string displayText)
{
    InitializeComponent();

    MainPage = new People.MainPage()
    {
        Text = displayText
    };
}

Pass platform-specific data to shared code

Our final step is to pass the database path from the platform-specific projects to the PCL so it can be displayed.

1. In each platform-specific project, find the code that instantiates the App class. This will be different on each platform.
2. Call the static FileAccessHelper.GetLocalFilePath method that you created earlier and pass in people.db3 as the file name parameter.
3. Pass the returned fully qualified filename into the App's constructor.

On iOS, this will be done in the AppDelegate:

public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
   ...
   public override bool FinishedLaunching(UIApplication app, NSDictionary options)
   {
      global::Xamarin.Forms.Forms.Init();
      string dbPath = FileAccessHelper.GetLocalFilePath("people.db3");
      LoadApplication(new App(dbPath));
      return base.FinishedLaunching(app, options);
   }
}

On Android, the App class is instantiated in the MainActivity:

public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsApplicationActivity
{
   protected override void OnCreate(Bundle bundle)
   {
      ...
      base.OnCreate(bundle);
      global::Xamarin.Forms.Forms.Init(this, bundle);
      string dbPath = FileAccessHelper.GetLocalFilePath("people.db3");
      LoadApplication(new App(dbPath));
   }
}

On Windows, the App class is instantiated in the code-behind for MainPage:

public partial class MainPage : global::Xamarin.Forms.Platform.WinPhone.FormsApplicationPage
{
   public MainPage()
   {
       this.InitializeComponent();
       string dbPath = FileAccessHelper.GetLocalFilePath("people.db3");
       LoadApplication(new People.App(dbPath));
   }
}

Run the application

Run the application on each platforms. They should all display the fully qualified database file path.

Remember to select a build configuration for each platform. For example, Windows UWP requires either x86 or x64 and iOS requires either iPhone or iPhoneSimulator.

Exercise summary

In this exercise, you retrieved the platform-specific database paths for each platform and displayed the result with the main page of the app. In a later exercise, you will extend this solution to connect to SQLite.

You can view the completed solution in the Exercise 1 > Completed folder of your copy of the cloned or downloaded course materials.