Monday, 11 April 2011

WP7 Tutorial - part 4: Storing Data on the Phone

If you want to save high scores or preferences you need persistent memory on the phone. On a traditional computer you would create a file and store your information in the file; another option on a Windows PC would be store such information in the registry. For security reasons there is no API to access the file system and there is no global persistent memory across applications on a WP7.

In general there are two ways to store data: (1) in a application specific storage (isolated storage) on the phone or (2) remotely on the internet (or to use another buzzword "in the cloud").
In this example the use of the phone isolated storage API is demonstrated. It is shown how to store and retrieve name-value pairs on the phone (to people who programmed Java ME this is conceptually similar to the record store).

For more details see: http://msdn.microsoft.com/en-us/library/cc221360(v=VS.95).aspx and page 126ff, C. Petzold, Programming Windows Phone 7. It is also possible to created an isolated storage for files see: http://msdn.microsoft.com/en-us/library/system.io.isolatedstorage.isolatedstoragefile(v=VS.95).aspx

See below the c# example using the local storage on a windows phone 7. You can also download the IsolatedStorageSettings project directory in a single ZIP-file.

using System;
using System.Windows;
using Microsoft.Phone.Controls;
using System.IO.IsolatedStorage;

// example of how to save to and load from the isolated application storage 
// this helps to create persistence storage within a single application
// in this example it is shown how to do it for a string 
// Albrecht Schmidt, University of Stuttgart  


// For more details see:
// http://msdn.microsoft.com/en-us/library/cc221360(v=VS.95).aspx
// page 126ff, C. Petzold, Programming Windows Phone 7

// storing files/directory structures see:
// http://msdn.microsoft.com/en-us/library/system.io.isolatedstorage.isolatedstoragefile(v=VS.95).aspx

namespace PhoneStorage
{
    public partial class MainPage : PhoneApplicationPage
    {
        // Constructor
        public MainPage()
        {
            InitializeComponent();
        }

        #region Save and Load Parameters from the Application Storage
        void saveToAppStorage(String ParameterName, String ParameterValue)
        {
            // use mySettings to access the Apps Storage
            IsolatedStorageSettings mySettings = IsolatedStorageSettings.ApplicationSettings;

            // check if the paramter is already stored
            if (mySettings.Contains(ParameterName))
            {
                // if parameter exists write the new value
                mySettings[ParameterName] = ParameterValue;
            }
            else
            {
                // if parameter does not exist create it
                mySettings.Add(ParameterName, ParameterValue);
            }
        }

        String loadFromAppStorage(String ParameterName)
        {
            String returnValue = "_notSet_";
            // use mySettings to access the Apps Storage
            IsolatedStorageSettings mySettings = IsolatedStorageSettings.ApplicationSettings;

            // check if the paramter exists
            if (mySettings.Contains(ParameterName))
            {
                // if parameter exists write the new value
                mySettings.TryGetValue<String>(ParameterName, out returnValue);
                // alternatively the following statement can be used:
                // returnValue = (String)mySettings[ParameterName];
            }

            return returnValue;
        }
        #endregion

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            saveToAppStorage("myIdentifer1", "Last used @ " + System.DateTime.Now.ToString("HH:mm:ss"));
            textBox1.Text = "saved...";
        }

        private void button2_Click(object sender, RoutedEventArgs e)
        {
            textBox1.Text = loadFromAppStorage("myIdentifer1");
        }

    }
}

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