Lecture # 7 Engr. Ali Javed 18th March, 2014

Transcription

1 Lecture # 7 Engr. Ali Javed 18 th March, 2014

2 Instructor s Information Instructor: Engr. Ali Javed Assistant Professor Department of Software Engineering U.E.T Taxila ali.javed@uettaxila.edu.pk Contact No: Office hours: Monday, 09:00-11:00, Office # 7 S.E.D Engr. Ali Javed

3 Course Information Course Name: Mobile Application Development Course Code: SE-5020 Course Link: Engr. Ali Javed

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5 Topics 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

6 Isolated Storage [1-2] Each application or game has its own particular data storage needs. The storage can be as simple as a name value pair (for example HighScore=100). On the other hand you might be storing an entire product database along with all your customers. Or you might be storing text documents or pictures taken with the phone camera. A Silverlight application will need to hold settings and information the user is working on and an XNA game will wantto store informationabout the progress of aplayerthrough the game along with high score and player settings. Windows phone programs can use isolated storage to hold this kind of information. This storage is called isolated because each application on the phone has its own area One applicationcannotaccessthestorageof another The data is storedin the massstorage of the phone Aprogramcan store verylargeamountsof datain isolated storage 6

7 Isolated Storage [1-2] The Isolated Storage area can hold very large amounts of data, up to the limit of the storage available in the phone itself. A will have at least 8G of built in storage which is shared between media (stored music, pictures and videos) and all the applications on the device. When an application is removed from the phone all the isolated storage assigned to it is deleted. When an application is upgraded via Marketplace (i.e. we release a new version of our program or game) the isolated storage retains the original contents. 7

8 Isolated Storage Locations You might also want to know the location of isolated storage files. This location is different depending on the operating system. The following table shows the root locations where isolated storage is created on a few common operating systems Operating system Windows 2000, Windows XP, Windows Server 2003 (upgrade from Windows NT 4.0) Windows clean installation (and upgrades from Windows 98 and Windows NT 3.51) Windows XP, Windows Server clean installation (and upgrades from Windows 2000 and Windows 98) Location in file system Roaming-enabled stores = <SYSTEMROOT>\Profiles\<user>\Application Data Nonroaming stores = <SYSTEMROOT>\Profiles\<user>\Local Settings\Application Data Roaming-enabled stores = <SYSTEMDRIVE>\Documents and Settings\<user>\Application Data Nonroaming stores = <SYSTEMDRIVE>\Documents and Settings\<user>\Local Settings\Application Data Roaming-enabled stores = <SYSTEMDRIVE>\Documents and Settings\<user>\Application Data Nonroaming stores = <SYSTEMDRIVE>\Documents and Settings\<user>\Local Settings\Application Data Windows 8, Windows 7, Windows Server 2008, Windows Vista Roaming-enabled stores = <SYSTEMDRIVE>\Users\<user>\AppData\Roaming Nonroaming stores = <SYSTEMDRIVE>\Users\<user>\AppData\Local 8

9 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 9

10 The Save button behaviour private void savebutton_click(object sender, RoutedEventArgs e) savetext("jot.txt", jottextbox.text); 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

11 The savetext method private void savetext(string filename, string text) using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication()) using (IsolatedStorageFileStream rawstream = isf.createfile(filename)) StreamWriter writer = new StreamWriter(rawStream); writer.write(text); writer.close(); The method can be used to save data in a file in isolated storage

12 Using IsolatedStorage private void savetext(string filename, string text) using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication()) using (IsolatedStorageFileStream rawstream = isf.createfile(filename)) StreamWriter writer = new StreamWriter(rawStream); writer.write(text); writer.close(); Obtains user-scoped isolated storage for use by an application The method starts by getting a reference to the isolated storage for this application IsolatedStorageFile Represents an isolated storage area containing files and directories

13 Creating a file private void savetext(string filename, string text) using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication()) using (IsolatedStorageFileStream rawstream = isf.createfile(filename)) StreamWriter writer = new StreamWriter(rawStream); writer.write(text); writer.close(); Initializes a new instance of the IsolatedStorageFileStream class giving access to the file designated by path, in the specified mode, and in the context of the IsolatedStorageFile specified by isf. Use this class to read, write and create files in isolated storage

14 Writing to the file private void savetext(string filename, string text) using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication()) using (IsolatedStorageFileStream rawstream = isf.createfile(filename)) StreamWriter writer = new StreamWriter(rawStream); writer.write(text); writer.close(); The method can nowwrite data to the file and close it StreamWriter Implements a TextWriter for writing characters to a stream Represents a writer that can write a sequential series of characters

15 The Load button behaviour private void loadbutton_click(object sender, RoutedEventArgs e) string text; if ( loadtext("jot.txt", out text ) ) jottextbox.text = text; else jottextbox.text = "Type your jottings here..."; The loadtextmethodtriesto openafile withthe nameit hasbeengiven. It thentries to readastringfromthatfile. If the file can be read correctly the loadtext method returns true and sets the output parameter to the contents of the file. Thisis thenusedto set the textin jottextbox. The load behaviour is more complex because the file might not be available If any part of the read operation fails the loadtext method returns false and jottextbox is set to a starting message.

16 Loading from Isolated storage try using (IsolatedStorageFileStream rawstream = isf.openfile(filename, System.IO.FileMode.Open)) StreamReader reader = new StreamReader(rawStream); result = reader.readtoend(); reader.close(); catch return false; Represents a reader that can read a sequential series of characters. This code reads a file from isolated storage It uses standard file input/output methods StreamReader Implements a TextReader that reads characters from a byte stream Note that it uses the ReadToEnd method to read from the file so that the program can read multi-line jottings.

17 Loading from Isolated storage try using (IsolatedStorageFileStream rawstream = isf.openfile(filename, System.IO.FileMode.Open)) StreamReader reader = new StreamReader(rawStream); result = reader.readtoend(); reader.close(); catch return false; Opens a file at a specified path using the specified sharing and access options. This member is overloaded OpenFile(String,FileMode) OpenFile(String,FileMode,FileAccess) OpenFile(String,FileMode,FileAccess,FileShare)

18 Loading from Isolated storage FileMode Specifieshowtheoperatingsystemshouldopenafile Member name Append Create CreateNew Description Opens the file if it exists and seeks to the end of the file, or creates a new file. Append can only be used in conjunction with Write. Specifies that the operating system should create a new file. If the file already exists, it will be overwritten. Create is equivalent to requesting that if the file does not exist, use CreateNew; otherwise, use Truncate. Specifies that the operating system should create a new file. Open Specifies that the operating system should open an existing file. A System.IO.FileNotFoundException is thrown if the file does not exist. OpenOrCreate Specifies that the operating system should open a file if it exists; otherwise, a new file should be created. Truncate Specifies that the operating system should open an existing file. Once opened, the file should be truncated so that its size is zero bytes.

19 Loading from Isolated storage FileAccess Definesconstantsforread,write,orread/writeaccessto afile Member name Read ReadWrite Write Description Read access to the file. Data can be read from the file. Combine with Write for read/write access. Read and write access to the file. Data can be written to and read from the file. Write access to the file. Data can be written to the file. Combine with Read for read/write access

20 Demo Demo 1: Jotpad Demo 20

21 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 In this case it seems a lot of effort to create files and streams just to store a simple value. To make it easy to store settings a program can 21 use the Isolated Storage settings store.

22 Settings and Dictionaries The settings storage works like a Dictionary collection Dictionaries are a very useful collection mechanism. A dictionary is made using two types. One is the type of the key, and the other is the type of the item being stored. 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 For example, we might create a class called Person which holds data about a person 22

23 A Dictionary example class Person public string Name; public string Address; public string 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

24 A Dictionary example [3] Dictionary<string, Person> Personnel = new Dictionary<string, Person>(); This creates a Dictionary called Personnel This holds a collection of Person records that are indexed on a string When we create a new Dictionary type we give it the type of the key (in this case a string because we are entering the name of the person) and the type of the item being stored (in this case a Person).

25 Storing in the Dictionary Person p1 = new Person Name = "Rob", Address = "His House", Phone = "1234" ; Personnel.Add(p1.Name, p1); This code makes a new Person instance and then stores it in the Personnel dictionary. The name value is used as the key The dictionary will not allow duplicate keys

26 Reading from a Dictionary Person findperson = Personnel["Rob"]; We can use a string indexer to locate items in the dictionary The findperson reference is set to refer to the Person instance with the name Rob. The dictionary does all the hard work of finding that particular entry. This makes it very easy to store large numbers of items and locate them later. The dictionary will refuse to store an item with the same key as one already present. In other words if I try to add a second person with the name Rob the Add operation will throw an exception. A program will also get an exception if it asks the dictionary for a record that doesn t exist:

27 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

28 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 For example we could add a second dictionary to our Personnel system that would allow us to find a person from their phone number 28

29 Dictionaries and Isolated Storage The IsolatedStorageSettings class provides a Dictionary based model for storing and retrieving setting information Provides a Dictionary<TKey, TValue> that stores key-value pairs in isolated storage. 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 29

30 Saving using settings private void savetext(string filename, string text) IsolatedStorageSettings isolatedstore = IsolatedStorageSettings.ApplicationSettings; isolatedstore.remove(filename); isolatedstore.add(filename, text); isolatedstore.save(); This Save method stores a string of text with the supplied name

31 Getting the isolated store private void savetext(string filename, string text) IsolatedStorageSettings isolatedstore = IsolatedStorageSettings.ApplicationSettings; isolatedstore.remove(filename); isolatedstore.add(filename, text); isolatedstore.save(); This statement gets a reference to the settings object Provides a Dictionary<TKey, TValue> that stores key-value pairs in isolated storage.

32 Removing an old version private void savetext(string filename, string text) IsolatedStorageSettings isolatedstore = 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

33 Saving the data private void savetext(string filename, string text) IsolatedStorageSettings isolatedstore = 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

34 SaveText Method This version of the savetext method uses the filename as the key. It removes an existing key with the given filename and then adds the supplied text as a new entry. The Remove method can be called to remove an item from a dictionary. It is given the key to the item to be removed. If the key is not present in the dictionary the Remove method returns false, but we can ignore this. Once we have made our changes to the store we need to call the Save method to persist these changes. 34

35 Reading from settings storage Reading is the reverse of writing Your program must provide the key of the item it wants to load The loadtext method fetches the requested item from the settings storage 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 35

36 Loading from the setting storage private bool loadtext(string filename, out string result) IsolatedStorageSettings isolatedstore = IsolatedStorageSettings.ApplicationSettings; result = ""; try result = (string)isolatedstore[filename]; catch return false; return true;

37 Managing the loading result = ""; try result = (string) isolatedstore[filename]; catch return false; 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 loadtext method failed 37 returns false to indicate that the load

38 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 We now have two ways to persist data on a device. We can store large amounts of data in a filestore that we can create and structure how we like. Alternatively we can store individual data items by name in a settings dictionary. 38

39 Demo 39

40 Reference Engr. Ali Javed 40

41 For any query Feel Free to ask Engr. Ali Javed 41