Persisting data in isolated storage

1. Persisting data in isolated storage Pongsakorn Poosankam Microsoft Innovation Center Manager Microsoft (Thailand) Limited

2. Topics • Windows Phone applications and isolated storage • Using isolated storage to store files • Storing name/value pairs • An introduction to the Dictionary collection class • Storing settings information in Isolated Storage

3. Isolated Storage • This storage is called isolated because each application on the phone has its own area • One application cannot access the storage of another • The data is stored in the mass storage of the phone • A program can store very large amounts of data in isolated storage

4. Jotpad program • This is the first version of the jotpad program • It displays a textbox for the user to enter text • It also has Load and Save buttons that can be used to load and save the jotted text to isolated storage

5. The Save button behaviour • When the user presses the Save button the event hander calls a method to save the text from the TextBox into a file • The saveText method is also given the name of the file to save the text in privatevoidsaveButton_Click(object sender, RoutedEventArgs e){saveText("jot.txt", jotTextBox.Text);}

6. The saveText method privatevoidsaveText(string filename, string text){using (IsolatedStorageFileisf =IsolatedStorageFile.GetUserStoreForApplication()) {using (IsolatedStorageFileStreamrawStream =isf.CreateFile(filename)) {StreamWriter writer = newStreamWriter(rawStream);writer.Write(text);writer.Close(); } }} • The method can be used to save data in a file in isolated storage

7. Using IsolatedStorage privatevoidsaveText(string filename, string text){using (IsolatedStorageFileisf =IsolatedStorageFile.GetUserStoreForApplication()) {using (IsolatedStorageFileStreamrawStream =isf.CreateFile(filename)) {StreamWriter writer = newStreamWriter(rawStream);writer.Write(text);writer.Close(); } }} • The method starts by getting a reference to the isolated storage for this application

8. Creating a file privatevoidsaveText(string filename, string text){using (IsolatedStorageFileisf =IsolatedStorageFile.GetUserStoreForApplication()) {using (IsolatedStorageFileStreamrawStream =isf.CreateFile(filename)) {StreamWriter writer = newStreamWriter(rawStream);writer.Write(text);writer.Close(); } }} • This reference is then used to create a stream connected to the newly created file

9. Writing to the file privatevoidsaveText(string filename, string text){using (IsolatedStorageFileisf =IsolatedStorageFile.GetUserStoreForApplication()) {using (IsolatedStorageFileStreamrawStream =isf.CreateFile(filename)) {StreamWriter writer = newStreamWriter(rawStream);writer.Write(text);writer.Close(); } }} • The method can now write data to the file and close it

10. The Load button behaviour privatevoidloadButton_Click(object sender, RoutedEventArgs e){string text;if ( loadText("jot.txt", out text ) ) {jotTextBox.Text = text; }else{jotTextBox.Text = "Type your jottings here...."; }} • The load behaviour is more complex because a the file might not be available • The load method displays a default message if loadText fails

11. Loading from Isolated storage try{using (IsolatedStorageFileStreamrawStream =isf.OpenFile(filename, System.IO.FileMode.Open)) {StreamReader reader = newStreamReader(rawStream); result = reader.ReadToEnd();reader.Close();}}catch {returnfalse;} • This code reads a file from isolated storage • It uses standard file input/output methods

12. The Isolated Storage File Store • Your applications can create many files in isolated storage • They can also build up a directory hierarchy within the storage • You can perform stream based input/output with files in the isolated storage

13. Demo Demo 1: Jotpad Demo

14. Using Settings Isolated storage • Creating files in isolated storage is useful, but often a program only wants to store name/value pairs • Examples of this: • Username • Home directory • Colour and display preferences • The Isolated storage in Windows Phone also provides setting storage

15. Settings and Dictionaries • The settings storage works like a Dictionary collection • A Dictionary holds a collection of a particular type which is indexed by key values of another type • Programs can look up items based on the value of the key

16. A Dictionary example classPerson{publicstring Name;publicstring Address;publicstring Phone;} • The Person class holds information about a given person in our system • The Person class could contain many more data properties than the ones above • We need to store and find Person items

17. A Dictionary example Dictionary<string, Person> Personnel = newDictionary<string, Person>(); • This creates a Dictionary called Personnel • This holds a collection of Person records that are indexed on a string • Generics are used to give the types of the index item and the data stored • We could use the name of the person as the index item

18. Storing in the Dictionary Person p1 = newPerson { Name = "Rob", Address = "His House", Phone = "1234" };Personnel.Add(p1.Name, p1); • This creates a Person value and adds it to the dictionary • The name value is used as the key • The dictionary will not allow duplicate keys

19. Reading from a Dictionary PersonfindPerson = Personnel["Rob"]; • We can use a string indexer to locate items in the dictionary • The Personnel dictionary will return Person values • If the item cannot be found this statement will throw an exception

20. Checking for Items if (Personnel.ContainsKey("Jim")){// If we get here the dictionary // contains Jim} • A Dictionary also provides a method that can be used to test for the existence of particular keys • Your code should do this rather than throw exceptions

21. Dictionaries in action • Dictionaries are very useful for storing collections that you want to index on a particular key value • The storing and searching is managed very efficiently • A system can contain multiple dictionaries to index on different key items • A program can also iterate through the dictionary contents

22. Dictionaries and Isolated Storage • The IsolatedStorageSettings class provides a Dictionary based model for storing and retrieving setting information • It stores any object indexed on a string key • This makes it very easy to store settings objects • Your application must call the “Save” method on the settings object to complete a save

23. Saving using settings privatevoidsaveText(string filename, stringtext){IsolatedStorageSettingsisolatedStore =IsolatedStorageSettings.ApplicationSettings;isolatedStore.Remove(filename);isolatedStore.Add(filename, text);isolatedStore.Save();} • This Save method stores a string of text with the supplied name

24. Getting the isolated store privatevoidsaveText(string filename, stringtext){IsolatedStorageSettingsisolatedStore =IsolatedStorageSettings.ApplicationSettings;isolatedStore.Remove(filename);isolatedStore.Add(filename, text);isolatedStore.Save();} • This statement gets a reference to the settings object

25. Removing an old version privatevoidsaveText(string filename, stringtext){IsolatedStorageSettingsisolatedStore =IsolatedStorageSettings.ApplicationSettings;isolatedStore.Remove(filename);isolatedStore.Add(filename, text);isolatedStore.Save();} • This removes an existing item with this name • Removing does not fail if the item is not there

26. Saving the data privatevoidsaveText(string filename, stringtext){IsolatedStorageSettingsisolatedStore =IsolatedStorageSettings.ApplicationSettings;isolatedStore.Remove(filename);isolatedStore.Add(filename, text);isolatedStore.Save();} • This adds the item and then saves the settings back to the isolated store

27. Saving items • You can save objects other than strings • Each object must have a unique name • Your program must call the Save method to persist the settings information when it has been added to the settings object

28. Reading from settings storage • Reading is the reverse of writing • Your program must provide the key of the item it wants to load • Note that the saved item will be returned in the form of an object reference which your program must cast to the required type • The settings storage does not provide a ContainsKey method

29. Loading from the setting storage privateboolloadText(string filename, outstring result) {IsolatedStorageSettingsisolatedStore = IsolatedStorageSettings.ApplicationSettings;result = "";try {result = (string)isolatedStore[filename];}catch {returnfalse;}returntrue;}

30. Managing the loading result = "";try {result = (string) isolatedStore[filename];}catch {returnfalse;} • Because it is not possible to check if a setting exists the load method must instead catch the exception that is thrown if a key is not found • The loatText method returns false to indicate that the load failed

32. Isolated Storage • A program can create and use as many files as the application requires • It is also possible to create folders within isolated storage so an application can organise data as required • The data will be persisted when the application is not running • If the application is removed from the phone all its isolated storage is deleted

33. Demo Demo 2: Settings Jotpad

34. Summary • Windows Phone provides “local” storage for applications • Data stored is local to an application and not shared with or visible to others • There is a local filesystem and a dictionary based setting store which can be used for name/value pairs