摘要:本文将带你了解Android开发之如何使用文件初始化sqlite数据库,希望本文对大家学Android有所帮助。
很多时候在应用安装初始化时,需要创建本地数据库,同时为数据库添加数据,之后再从数据库中读取数据。
这里有2个思路
1.先在本地创建一个能支持android使用的sqlite数据库文件,启动时,用现成的sqlite的二进制文件进行直接copy到Android系统的数据库路径
2.可以考虑在第一次启动时,执行数据库初始化的sql文件.
1.在本地准备android能使用的sqlite数据库文件
使用sqlite数据库管理工具,看个人爱好(SQLite Database Browser ,Navicat Premium,)
打开数据库,创建"android_metadata"数据表
Sql代码
1. CREATE TABLE "android_metadata" ("_id" INTEGER PRIMARY KEY AUTOINCREMENT,"locale" TEXT DEFAULT ‘en_US‘);//创建表
2. INSERT INTO "android_metadata" VALUES (1,‘en_US‘);//插入值
创建其他应用需要的表..此处省略.
2.复制文件到应用中.
把第一步创建的数据库文件复制到应用中的assets文件夹, asserts文件夹的路径如下:
然后创建DateBaseHelper extends SQLiteOpenHelper的类文件.
代码如下:
Java代码
1. public class DataBaseHelper extends SQLiteOpenHelper { 2. //The Android‘s default system path of your application database. 3. private static String DB_PATH = "/data/data/YOUR_PACKAGE/databases/"; 4. private static String DB_NAME = "myDBName"; 5. private SQLiteDatabase myDataBase; 6. private final Context myContext; 7. /** 8. * Constructor 9. * Takes and keeps a reference of the passed context in order to access to the application assets and resources. 10. * @param context 11. */ 12. public DataBaseHelper(Context context) { 13. super(context, DB_NAME, null, 1); 14. this.myContext = context; 15. } 16. 17. /** 18. * Creates a empty database on the system and rewrites it with your own database. 19. * */ 20. public void createDataBase()throws IOException { 21. boolean dbExist = checkDataBase(); 22. if (dbExist) { 23. //do nothing - database already exist 24. } else { 25. //By calling this method and empty database will be created into the default system path 26. //of your application so we are gonna be able to overwrite that database with our database. 27. this.getReadableDatabase(); 28. try { 29. copyDataBase(); 30. } catch (IOException e) { 31. throw new Error("Error copying database"); 32. } 33. } 34. } 35. 36. /** 37. * Check if the database already exist to avoid re-copying the file each time you open the application. 38. * @return true if it exists, false if it doesn‘t 39. */ 40. private boolean checkDataBase() { 41. SQLiteDatabase checkDB = null; 42. try { 43. String myPath = DB_PATH + DB_NAME; 44. checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY); 45. } catch (SQLiteException e) { 46. //database does‘t exist yet. 47. } 48. 49. if (checkDB != null) { 50. checkDB.close(); 51. } 52. return checkDB != null ? true : false; 53. } 54. 55. /** 56. * Copies your database from your local assets-folder to the just created empty database in the 57. * system folder, from where it can be accessed and handled. 58. * This is done by transfering bytestream. 59. * */ 60. private void copyDataBase()throws IOException { 61. //Open your local db as the input stream 62. InputStream myInput = myContext.getAssets().open(DB_NAME); 63. // Path to the just created empty db 64. String outFileName = DB_PATH + DB_NAME; 65. //Open the empty db as the output stream 66. OutputStream myOutput = new FileOutputStream(outFileName); 67. //transfer bytes from the inputfile to the outputfile 68. byte[]buffer = new byte[1024]; 69. int length; 70. while ((length = myInput.read(buffer)) > 0) { 71. myOutput.write(buffer, 0, length); 72. } 73. 74. //Close the streams 75. myOutput.flush(); 76. myOutput.close(); 77. myInput.close(); 78. } 79. 80. public void openDataBase()throws SQLException { 81. //Open the database 82. String myPath = DB_PATH + DB_NAME; 83. myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY); 84. } 85. 86. @Override 87. public synchronized void close() { 88. if (myDataBase != null) 89. myDataBase.close(); 90. super.close(); 91. } 92. 93. @Override 94. public void onCreate(SQLiteDatabase db) {} 95. 96. @Override 97. public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {} 98. // Add your public helper methods to access and get content from the database. 99. // You could return cursors by doing "return myDataBase.query(....)" so it‘d be easy 100. // to you to create adapters for your views. 101. } 3.现在我们可以创建DateBaseHelper的实现操作了. createDataBase() //创建 openDataBase()//打开只读数据库 记得要更改"YOUR_PACKAGE"为你的应用的包名 如:com.examplename.myapp 大概代码如下: Java代码 1. ... 2. DataBaseHelper myDbHelper = new DataBaseHelper(); 3. myDbHelper = new DataBaseHelper(this); 4. try { 5. myDbHelper.createDataBase(); 6. } catch (IOException ioe) { 7. throw new Error("Unable to create database"); 8. } 9. try { 10. myDbHelper.openDataBase(); 11. } catch (SQLException sqle) { 12. throw sqle; 13. } 14. ...
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