Summary of four data access methods for Android applications

ArticleDirectory

• 1. Use shared preferences:
• 2. Use file:
• 3. Network Space: (omitted)
• 4. SQLite database:

1. Use shared preferences:

Save Android applications in one sentenceProgramConfiguration information:

Save: getpreferences (activity. mode_private). Edit (). putstring (strkey, strvalue). Commit ();

Read: strvalue = getpreferences (activity. mode_private). getstring (strkey, strdefault );

Note: getsharedpreferences () is used for configuration data sharing between different activities in the application ().

2. Use file:

Files data storage mainly uses properties and works with fileinputstream or fileoutputstream to write files.

Save:

Fileoutputstream stream = This. openfileoutput (filename, context. mode_private );

New properties (). Put (strkey, strvalue). Store (stream ,"");

Read:

Fileinputstream stream = This. openfileinput (filename );

Strvalue = string. valueof (new properties (). Load (Stream). getproperty (strkey ));

Note: using the setproperty () method of properties, You can package key-value pairs, and finally call the storexxx method to write data to the file.

3. Network Space: (Omitted) 4. SQLite database:

A, SQLitePrerequisites:

Default database path:Data/data/mypackage/databases/

Open the database:Sqlite3 dbname

Operation:. HelpHelp;. TableView All Tables

Every sentenceSQLA semicolon is required to end the statement.;

B, JDBCDriver:

Class. forname ("org. SQLite. JDBC ");

Connection conn = drivermanager. getconnection ("JDBC: SQLite: FILENAME"); // filenameFor yourSQLiteData name

C,UseSqliteopenhelperDatabase Operations:

Obtain database instances:

Getreadabledatabase ()Obtain readableSqlitedatabase

Getwritabledatabase ()Obtain writableSqlitedatabase

SqliteopenhelperCommon events to be overwritten in subclass:

Oncreate (sqlitedatabase)

Ondowngrade (sqlitedatabase dB, int oldversion, int newversion)

Onupgrade (sqlitedatabase dB, int oldversion, int newversion)

EncapsulatedDbhelpClass to perform database operations:

Public class dbhelp extends sqliteopenhelper {

Public dbhelp (context, string name, cursorfactory factory,

Int version ){

Super (context, name, factory, version );

}

@ Override

Public void oncreate (sqlitedatabase dB ){

Db.exe csql (createtablesql );//RunSQLNeed to useExecsql()

}

@ Override

Public void onupgrade (sqlitedatabase dB, int oldversion, int newversion ){

}

@ Override

Public void onopen (sqlitedatabase dB ){

}

Insertdata ()

Updatedata ()

Deletedata ()

Rawquery ()

Query ()

}

Create and open a database:

Sqlitedatabase DB = new dbhelp (sqliteactivity. This). getreadabledatabase ();

Add data:

Dbhelp = new dbhelp (sqliteactivity. This );

Sqlitedatabase DB = dbhelp. getwritabledatabase ();

Contentvalues = new contentvalues ();

Contentvalues. Put ("sname", txtname. gettext (). tostring ());

Contentvalues. Put ("ssex ","Male");

Dbhelp. insertdata (dB, contentvalues);

Modify data:

Dbhelp = new dbhelp (sqliteactivity. This );

Sqlitedatabase DB = dbhelp. getwritabledatabase ();

Contentvalues = new contentvalues ();

Contentvalues. Put ("sname", txtsname. gettext (). tostring ());

String whereclause = "SID =? ";//Which of the following conditions must be modified? Placeholder

String [] whereargs = new string [] {txtsid. gettext (). tostring ()};

Dbhelp. updatedata (dB, contentvalues, whereclause, whereargs);

Delete data:

Dbhelp = new dbhelp (sqliteactivity. This );

Sqlitedatabase DB = dbhelp. getwritabledatabase ();

String whereclause = "SID =? ";//Use the condition value of the data to be deleted? Placeholder

String [] whereargs = new string [] {txtid. gettext (). tostring ()};

Dbhelp. deletedata (dB, whereclause, whereargs);

Query data:

Cursor cur = dB. rawquery ("select * from student where Sid = 1 and sname = 'hangsan'", null );

Cursor cur = dB. rawquery (...)

EveryRawquery ()OrQuery ()ReturnsSQLiteDatabaseCursor.

Operation cursor:

UseGetcount ()Method to obtain the number of records in the result set;

PassMovetofirst (), movetonext (),AndIsafterlast ()Method to traverse all records;

PassGetcolumnnames ()Obtain the field name;

PassGetcolumnindex ()Convert to a field number;

PassGetstring (),Getint ()To obtain the value of the current record of the given field;

PassRequery ()Method re-run the query to get the cursor;

PassClose ()Method to release the cursor resource;

Simplecursoradapter: Associated with the cursor, boundListviewTo present data,Prerequisites: The table has_ IdColumn, which is the primary key.

Simplecursoradapter simple = new simplecursoradapter (sqliteactivity. this, android. r. layout. simple_list_item_1, cur, new string [] {"sname", "ssex"}, new int [] {android. r. id. text1, android. r. id. text2 });

Studentlist. setadapter (simple );

When_ IdWhen it is not a primary key, the cursor first retrieves the data and then usesSimpleadapterTo present data:

Arraylist

Hashmap <string, Object> HS;

For (cur. movetofirst ();! Cur. isafterlast (); cur. movetonext ()){

HS = new hashmap <string, Object> ();

HS. Put ("Sid", cur. getint (cur. getcolumnindex ("Sid ")));

HS. Put ("sname", cur. getstring (cur. getcolumnindex ("sname ")));

HS. Put ("ssex", cur. getstring (cur. getcolumnindex ("ssex ")));

Students. Add (HS );

}

Simpleadapter SIM = new simpleadapter (sqliteactivity. this, students, android. r. layout. simple_list_item_1, new string [] {"sname", "ssex"}, new int [] {android. r. id. text1, android. r. id. text2 });

Studentlist. setadapter (SIM );

 

Conclusion