A summary of data preservation methods in Android application development _android

One, save the file to the phone memory

/**
   * Save the data to the cell phone rom file.
   * @param context Application contexts provide environment
   * @param name username
   * @param password Password
   * @throws Exception * *
   public
St atic void Savetorom (context context, string name, string password) throws exception{//file
    file = new file ("/data/da Ta/com.itheima.login/files/info.txt ");
    File File = new file (Context.getfilesdir (), "info.txt");//The file is under the Files folder under Data Getcachedir () under the cache folder size not exceeding 1Mb
    FileOutputStream fos = new FileOutputStream (file);
    String txt = name+ ":" +password;
    Fos.write (Txt.getbytes ());
    Fos.flush ();
    Fos.close ();
  }

/**
   * Gets the saved data
   * @param context
   * @return
/public static map<string,string> GetUserInfo ( Context context) {
    File File = new file (Context.getfilesdir (), "Info.txt");
    try {
      FileInputStream fis = new FileInputStream (file);
      You can also directly read the file string result = Streamtools.readfromstream (FIS);
      BufferedReader br = new BufferedReader (new InputStreamReader (FIS));
      String str = br.readline ();
      string[] Infos = Str.split (":");
      map<string,string> map = new hashmap<string, string> ();
      Map.put ("username", infos[0]);
      Map.put ("Password", infos[1]);
      return map;
    } catch (Exception e) {

      e.printstacktrace ();
      return null;
    }

  }
Finally, the above method can be directly invoked to read the information
map<string, string> Map = GetUserInfo (this);
If (map!=null) {
textview.settext (map.get ("username"));
}

Second, save the file to the SD card
to get the size of the cell phone SD space:

File path = Environment.getexternalstoragedirectory ();
    Statfs stat = new Statfs (Path.getpath ());
    Long blockSize = Stat.getblocksize ();
    Long totalblocks = Stat.getblockcount ();
    Long availableblocks = Stat.getavailableblocks ();
    Long totalsize = blocksize*totalblocks;
    Long availsize = blockSize * availableblocks;

    String totalstr = formatter.formatfilesize (this,totalsize);
    String availstr = Formatter.formatfilesize (this, availsize);
    Tv.settext ("Total space" +totalstr+ "\ n" + "free Space" +availstr);

To add permission to write external storage:

 <uses-permission android:name= "Android.permission.WRITE_EXTERNAL_STORAGE"/> public static void Save (string name, string password) throws exception{if (Environment.getexternalstoragestate (). equals (environment.media_mounted)) {File File = new file (Environment.getexternalstoragedirectory (), "info.txt");///write directly/sdcard/info.txt to determine if SD card exists Fileo
    Utputstream fos = new FileOutputStream (file);
    String txt = name+ ":" +password;
    Fos.write (Txt.getbytes ());
    Fos.flush ();
Fos.close ();
Using randomaccessfile like file append content FileOutputStream will empty the original file contents//randomaccessfile RAF = new Randomaccessfile (file, "RW"); Raf.seek (File.length ());
Move the file pointer to the last//raf.write (Name.getbytes () +password.getbytes ());
  Raf.close (); }
}

Read file add Read permission public
static String read () {
      try {
        if (environment.getexternalstoragestate (). Equals ( environment.media_mounted)) {
          File sdcarddir = Environment.getexternalstoragedirectory ();
          FileInputStream fis = new FileInputStream (Sdcarddir.getcanonicalpath () + "Info.txt");
          BufferedReader br = new BufferedReader (new InputStreamReader (FIS));
          StringBuilder sb = new StringBuilder ("");
          String line = null;
          while (line = Br.readline ())!= null) {
            sb.append (line);
          return sb.tostring ();
        }
      catch (Exception e) {

        e.printstacktrace ();
      }
      return null;
    }

Third, the use of sharedpreferences
sharedpreference is commonly used in the development of a storage mode, mainly store some of the system invariant parameters such as whether it is the first time into the application, and so on, through the way of key-value pair storage
Types that can be stored: booleans, floats, ints, longs,strings.

Getsharedpreferences ()-Storing multiple parameters
Getpreferences ()-stores only one parameter and does not need to specify a name (key)
Steps to write:

Sharedpreferences call edit () to get a editor object
Add a value using Putboolean () and putstring ()
Commit TRANSACTION Completion Storage
READ: Just call Sharedpreferences Getboolean () and getString ()

Here is the sample code:

public class Mysharedpreference {
  private context context;
  Private Sharedpreferences sp;
  Private Editor edit;
  Public Mysharedpreference {
    This.context = context;
  }
  public boolean savemessage (String name,string pwd) {
    Boolean flag = false;
     SP = context.getsharedpreferences ("UserInfo", context.mode_private);
     Mode defines the access right now that this application can access
    edit = Sp.edit ();
    Edit.putstring ("name", name);
    Edit.putstring ("pwd", pwd);
    Flag = Edit.commit ()//commits the transaction to persist the data to the storage return
    flag

  ;
  Public map<string,object> GetMessage () {
    map<string,object> Map = new hashmap<string, object> () ;
    SP = context.getsharedpreferences ("UserInfo", context.mode_private);
    String name = sp.getstring ("name", "");
    String pwd = sp.getstring ("pwd", "");
    Map.put ("name", name);
    Map.put ("pwd", pwd);
    return map;

  }