Application Preferences

Many applications are required to save data in the persistent memory and read them in the next session in a safe way. Saved data can be sensitive, so in many cases access to the saved preference should be restricted. Preference API allows you to share stored preference data among applications in the same package.

Store and retrieve records

To store a variable, you must create a key-value pair. Use the following function to create a preference for a specific simple type: Preference.Set(string key, value).

Before storing or retrieving a variable, check whether it exists using the Preference.Contains(string key) function. Use the following function to retrieve a stored variable: Preference.Get<T>():

                
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//set/get integer value
Preference.Set("test_integer", 10);

if (Preference.Contains("test_integer"))
{
    var testInt = Preference.Get<int>("test_integer");
}

To store and retrieve string variables, use the following functions:

• Preference.Set("test_string", "TEST VALUE")
• Preference.Get<string>("test_string")

List records

To list all records, use Keys collection Preference.Keys():

                
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  Preference.Set("Option_enabled", true);
  Preference.Set("active_user", "Joe");
  Preference.Set("default_volume", 10);
  Preference.Set("brightness", "0.6");

  foreach(string key in Preference.Keys)
  {
      Tizen.Log.Info("TEST", string.Format("Key name: {0}", key));
  }

Remove records

To safely remove records, use Preference.Remove(string key):

                
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    if (Preference.Contains("key"))
    {
        Preference.Remove("key");
    }

To remove all records, use the following function:

• Preference.RemoveAll()

Manage application preferences

The following code snippet shows how to store counter value when the application is closed using Tizen.Applications.Preference module.

Figure: Preference Application Screenshot

The clicked counter is stored as a pair of key-value data. When the application starts it tries to read this value and inserts it in the label component. To use NUI components and Preference module, the following namespaces are included:

                
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using System;

using Tizen.NUI;
using Tizen.NUI.BaseComponents;
using Tizen.NUI.Components;

using Tizen.Applications;

The ClickedPreferenceKey key is used to store counter value. It has to be declared as a class member for it to be used in button callbacks. Also, the TextLabel has to be a class member to show and update the counter value:

                
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namespace NUIPreference
{
    class Program : NUIApplication
    {
        private readonly string LogTag = "NUI_Application";
        private readonly string ClickedPreferenceKey = "clicked_counter";

        private int ClickedCounter = 0;

        private TextLabel ResultViewer;

        //...
    }
}

The OnCreate() handler tries to read value from the Preference module. Try/Catch block is useful when ClickedPreferenceKey is not set previously:

                
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protected override void OnCreate()
{
    base.OnCreate();

    try
    {
        ClickedCounter = Preference.Get<int>(ClickedPreferenceKey);
    } catch (Exception e) {
        Tizen.Log.Error(LogTag, e.ToString());
    }

    Initialize();
}

In OnTerminate() method you can save key-value pairs:

                
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protected override void OnTerminate()
{
    Preference.Set(ClickedPreferenceKey,  ClickedCounter);
    base.OnTerminate();
}

The CreateButtons() method is a helper function. It is responsible for the following:

• Creating buttons layout,
• Creating buttons,
• Setup callbacks:

                
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private View CreateButtons()
{
    View buttonsContainer = new View()
    {
        WidthResizePolicy = ResizePolicyType.FillToParent,
        HeightResizePolicy = ResizePolicyType.FitToChildren,
        Layout = new LinearLayout()
        {
            HorizontalAlignment = HorizontalAlignment.Center,
            LinearOrientation = LinearLayout.Orientation.Horizontal
        }
    };

    var btnSize = new Size2D(220, 80);

    var addButton = new Button() { Size2D = btnSize, Text = "+" };
    var decButton = new Button() { Size2D = btnSize, Text = "-" };
    var saveButton = new Button() { Size2D = btnSize, Text = "Save" };
    var removeButton = new Button() { Size2D = btnSize, Text = "Remove" };

    addButton.Clicked += OnAddClicked;
    decButton.Clicked += OnDecClicked;
    saveButton.Clicked += OnSaveClicked;
    removeButton.Clicked += OnRemoveClicked;

    buttonsContainer.Add(addButton);
    buttonsContainer.Add(decButton);
    buttonsContainer.Add(saveButton);
    buttonsContainer.Add(removeButton);

    return buttonsContainer;
}

The Initialize() function creates application layout and components:

                
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void Initialize()
{
    Window.Instance.KeyEvent += OnKeyEvent;

    View rootView = new View()
    {
        BackgroundColor = Color.White,
        WidthResizePolicy = ResizePolicyType.FillToParent,
        HeightResizePolicy = ResizePolicyType.FillToParent,
        Layout = new LinearLayout()
        {
            CellPadding = new Size2D(30, 30),
            Padding = new Extents(30, 30, 30, 30),
            LinearOrientation = LinearLayout.Orientation.Vertical
        }
    };

    var buttonsContainer = CreateButtons();
    rootView.Add(buttonsContainer);

    ResultViewer = new TextLabel()
    {
        Text = string.Format("Current Counter: {0}", ClickedCounter)
    };

    rootView.Add(ResultViewer);
    Window.Instance.GetDefaultLayer().Add(rootView);
}

The OnAddClicked() handler increase the counter and update the result label value:

                
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public void OnAddClicked(object sender, ClickedEventArgs e)
{
    ClickedCounter++;
    ResultViewer.Text = string.Format("Current Counter: {0}", ClickedCounter);
}

The OnDecClicked() handler decrease the counter and also update the label:

                
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public void OnDecClicked(object sender, ClickedEventArgs e)
{
    ClickedCounter--;
    ResultViewer.Text = string.Format("Current Counter: {0}", ClickedCounter);
}

The OnSaveClicked() handler saves the ClickedCounter value in the preference module:

                
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public void OnSaveClicked(object sender, ClickedEventArgs e)
{
    Preference.Set(ClickedPreferenceKey, ClickedCounter);
}

The OnRemoveClicked() handler resets ClickedCounter value and removes it from the Preference module:

                
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public void OnRemoveClicked(object sender, ClickedEventArgs e)
{
    try
    {
        Preference.Remove(ClickedPreferenceKey);
    } catch (Exception error) {
        Tizen.Log.Error(LogTag, error.ToString());
    }

    ClickedCounter = 0;
    ResultViewer.Text = string.Format("Current Counter: {0}", ClickedCounter);
}

Application entry point:

                
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static void Main(string[] args)
{
    var app = new Program();
    app.Run(args);
}

Related information

• Dependencies
  • Tizen 2.4 and Higher