1、基於軟硬整合觀點(diǎn)F06_d觀摩：ContentProvider架構(gòu)與DB引擎移植方法( d)By 高煥堂基於軟硬整合觀點(diǎn)5、展現(xiàn)DB引擎的變換自由度：以Linter引擎的移植為例 在上一個(gè)范例里，Client使用ContentProvider接口與SQLite DB引擎銜接。 onCreate() DataPersist對(duì)象是由Android框架所創(chuàng)建的。 之后，Client就調(diào)用getContentResolver() 函數(shù)來(lái)要求Android框架去進(jìn)行配對(duì)和綁定此DataPersist對(duì)象。然后間接綁定了Linter DB引擎。 此ContentProvider接口與特定DB引擎是無(wú)關(guān)的，

2、可以讓Client與DB引擎互為獨(dú)立。非常有助于雙方的獨(dú)立成長(zhǎng)，或各自的版 本更新，甚至新DB引擎的移植。 例如，我們先將Linter DB引擎安裝到Android的Linux環(huán)境里，并建立JDBC存取通道；接著就我們能輕易地將Linter引擎整合到ContentProvider框架里。 這包含了3個(gè)類：1. LinterPersist類2. LinterCursor類3. DispActivity類 LinterPersist類實(shí)現(xiàn)query()接口，實(shí)際呼叫Linter數(shù)據(jù)庫(kù)的功能。 也就是說(shuō)，DispActivity透過(guò)ContentProvider接口呼叫到LinterPersist

3、的query()函數(shù)。 此時(shí)創(chuàng)建一個(gè)LinterCursor對(duì)象，將其Cursor接口回傳給DispActivity 。onCreate()connect() 此LinterPersist對(duì)象是由Android框架所創(chuàng)建的。 之后，Client就調(diào)用getContentResolver() 函數(shù)來(lái)要求Android框架去進(jìn)行配對(duì)和綁定此LinterPersist對(duì)象。然后間接綁定了Linter DB引擎。 Linter + Android 范例代碼 于此，我們需要撰寫3個(gè)類：1. LinterPersist類2. LinterCursor類3. DispActivity類/* - Linter

4、Persist.java 程序代碼*/ .public class LinterPersist extends ContentProvider private static final StringLINTER_TABLE_NAME= Student123;Override public boolean onCreate() try Class.forName(com.relx.jdbc.LinterDriver).newInstance(); con = DriverManager.getConnection( jdbc:Linter:linapid:localhost:1070:local

5、, SYSTEM,MANAGER); catch(Exception e) Log.e(Conn failed, e.toString(); return false;try Statement stmt = con.createStatement(); stmt.executeUpdate(drop table +LINTER_TABLE_NAME); catch (Exception e) Log.e(drop table failed, e.toString(); try Statement stmt = con.createStatement(); stmt.executeUpdate

6、( create table +LINTER_TABLE_NAME + (stud_no char(10),stud_name char(20);); PreparedStatement prepstmt1 = con.prepareStatement(insert into + LINTER_TABLE_NAME + values (?,?);); prepstmt1.setString(1, linter_5);prepstmt1.setString(2, Lisa); prepstmt1.executeUpdate();prepstmt1.setString(1, linter_8);p

7、repstmt1.setString(2, Kitty); prepstmt1.executeUpdate( ); catch (Exception e) Log.e(create/insert table failed,e.toString();return false; return true;Override public Cursor query(Uri uri, String projection, String selection,String selectionArgs, String sortOrder) ResultSet rs = null;try Statement st

8、mt = con.createStatement(); rs = stmt.executeQuery(select * from +LINTER_TABLE_NAME); catch (Exception e) e.printStackTrace(); return null; Cursor c = new LinterCursor(rs, con); return c;Overridepublic String getType(Uri uri) return null;Override public Uri insert(Uri uri, ContentValues initialValue

9、s) String field_1 = initialValues.get(stud_no).toString(); String field_2 = initialValues.get(stud_name).toString(); try PreparedStatement prepstmt1 = con.prepareStatement(insert into + LINTER_TABLE_NAME + values (?,?);); prepstmt1.setString(1, field_1);prepstmt1.setString(2, field_2); prepstmt1.exe

10、cuteUpdate(); catch (Exception e) Log.e(ERROR, e.toString(); return uri;Override public int delete(Uri uri, String where, String whereArgs) return 0; Override public int update(Uri uri, ContentValues values, String where,String whereArgs) return 0;/ 定義LinterCursor 類 class LinterCursor implements Cur

11、sorResultSet res;Connection conn; LinterCursor( ResultSet rs, Connection con) res = rs;conn = con; Overridepublic void close() try res.close();conn.close(); catch (java.sql.SQLException e) e.printStackTrace();Overridepublic void copyStringToBuffer(int columnIndex, CharArrayBuffer buffer) Override pu

12、blic void deactivate() Override public byte getBlob(int columnIndex) return null; Override public int getColumnCount() return 0; Override public int getColumnIndex(String columnName)return 0; Overridepublic int getColumnIndexOrThrow(String columnName) throws IllegalArgumentException return 0;Overrid

13、e public String getColumnName(int columnIndex)return null;Override public String getColumnNames() return null;Override public int getCount() return 0;Override public double getDouble(int columnIndex) return 0;Override public Bundle getExtras() return null; Override public float getFloat(int columnIn

14、dex) return 0;Override public int getInt(int columnIndex) return 0;Override public long getLong(int columnIndex) return 0; Override public int getPosition() return 0;Override public short getShort(int columnIndex) return 0; Override public String getString(int columnIndex) try return res.getString(c

15、olumnIndex + 1); catch (java.sql.SQLException e) e.printStackTrace(); return null;Override public boolean getWantsAllOnMoveCalls() return false;Override public boolean isAfterLast() try return res.isAfterLast(); catch (java.sql.SQLException e) e.printStackTrace(); return false; Override public boole

16、an isBeforeFirst() try return res.isBeforeFirst(); catch (java.sql.SQLException e)e.printStackTrace(); return false; Override public boolean isClosed() return false; Override public boolean isFirst() return false; Override public boolean isLast() return false; Override public boolean isNull(int colu

17、mnIndex) return false; Override public boolean move(int offset) return false; Override public boolean moveToFirst() try return res.first(); catch (java.sql.SQLException e) e.printStackTrace(); return false; Override public boolean moveToLast() return false; Override public boolean moveToNext() try r

18、eturn res.next(); catch (java.sql.SQLException e)e.printStackTrace(); return false; Override public boolean moveToPosition(int position)return false;Override public boolean moveToPrevious() return false; Override public void registerContentObserver(ContentObserver observer) Override public void regi

19、sterDataSetObserver(DataSetObserver observer) return null; Override public boolean requery() return false; Override public Bundle respond(Bundle extras) Override public void setNotificationUri(ContentResolver cr, Uri uri) Override public void unregisterContentObserver(ContentObserverobserver)Overrid

20、e public void unregisterDataSetObserver(DataSetObserver observer) LinterPersist類里的指令：Override public Cursor query(Uri uri, String projection, String selection, String selectionArgs, String sortOrder)ResultSet rs = null;try Statement stmt = con.createStatement(); rs = stmt.executeQuery(select * from

21、+LINTER_TABLE_NAME); catch (Exception e) e.printStackTrace(); return null; Cursor c = new LinterCursor(rs, con); return c;此函數(shù)呼叫了Linter的executeQuery()函數(shù)，要求Linter進(jìn)行數(shù)據(jù)庫(kù)的查詢?nèi)蝿?wù)。Linter回傳一個(gè)ResultSet對(duì)象，讓應(yīng)用程序可瀏覽所查詢到的各筆數(shù)據(jù)。在這query()函數(shù)里，就誕生一個(gè)LinterCursor 對(duì)象，讓它內(nèi)含該ResultSet對(duì)象，然后將此LinterCursor對(duì)象回傳給DispActivity應(yīng)用類。

22、于是，順利地將Linter數(shù)據(jù)庫(kù)配上ContentProvider接口，飛上枝頭變鳳凰， 成為Android嫡系成員。 終于完成我們的目：讓遠(yuǎn)從之外的Linter舶來(lái)組件，順利融入(移植到)Android之中，成為其嫡系成員之一/* - DispActivity.java*/ public class DispActivity extends ListActivity public static final String AUTHORITY= vider.rx09-04; public static final Uri CONTENT_URI= Uri.parse(c

23、ontent:/ + AUTHORITY +/Stud202);private static final String PROJECTION=new String stud_no, stud_name;Override protected void onCreate(Bundle savedInstanceState) super.onCreate(savedInstanceState);Intent intent = getIntent();if (intent.getData() = null) intent.setData(CONTENT_URI); Cursor cursor = ge

24、tContentResolver().query(getIntent().getData(),PROJECTION, null, null, null);if(cursor = null)return;ArrayListMap coll= new ArrayListMap(); Map item; cursor.moveToFirst();while (!cursor.isAfterLast() item = new HashMap(); item.put(c1, cursor.getString(0) + , +cursor.getString(1);coll.add(item); cursor.moveToNext();this.setListAdapter