當LauncherProvider.DatabaseHelper.convertDatabase（SQLiteDatabase db）在Android默認啓動器中返回true時？

Question

我在閱讀Android 2.2默認啓動器的源代碼時遇到問題。
LauncherProvider.DatabaseHelper的源代碼段：

@Override 
public void onCreate(SQLiteDatabase db) { 
    if (LOGD) 
    Log.d(TAG, "creating new launcher database"); 

    db.execSQL("CREATE TABLE favorites (" + "_id INTEGER PRIMARY KEY," 
     + "title TEXT," + "intent TEXT," + "container INTEGER," 
     + "screen INTEGER," + "cellX INTEGER," + "cellY INTEGER," 
     + "spanX INTEGER," + "spanY INTEGER," + "itemType INTEGER," 
     + "appWidgetId INTEGER NOT NULL DEFAULT -1," 
     + "isShortcut INTEGER," + "iconType INTEGER," 
     + "iconPackage TEXT," + "iconResource TEXT," + "icon BLOB," 
     + "uri TEXT," + "displayMode INTEGER" + ");"); 

    // Database was just created, so wipe any previous widgets 
    if (mAppWidgetHost != null) { 
    mAppWidgetHost.deleteHost(); 
    sendAppWidgetResetNotify(); 
    } 

    if (!convertDatabase(db)) { 
    // Populate favorites table with initial favorites 
    loadFavorites(db); 
    } 
} 

private boolean convertDatabase(SQLiteDatabase db) { 
    if (LOGD) 
    Log.d(TAG, 
     "converting database from an older format, but not onUpgrade"); 
    boolean converted = false; 

    final Uri uri = Uri.parse("content://" + Settings.AUTHORITY 
     + "/old_favorites?notify=true"); 
    final ContentResolver resolver = mContext.getContentResolver(); 
    Cursor cursor = null; 

    try { 
    cursor = resolver.query(uri, null, null, null, null); 
    } catch (Exception e) { 
    // Ignore 
    } 

    // We already have a favorites database in the old provider 
    if (cursor != null && cursor.getCount() > 0) { 
    try { 
     converted = copyFromCursor(db, cursor) > 0; 
    } finally { 
     cursor.close(); 
    } 

    if (converted) { 
     resolver.delete(uri, null, null); 
    } 
    } 

    if (converted) { 
    // Convert widgets from this import into widgets 
    if (LOGD) 
     Log.d(TAG, "converted and now triggering widget upgrade"); 
    convertWidgets(db); 
    } 

    return converted; 
} 

onCreate()被調用來創建數據庫當在系統中沒有數據庫。在onCreate（）的尾部，它調用convertDatabase（SQLiteDatabase db）。並且在convertDatabase（SQLiteDatabase數據庫）中有查詢代碼。我很困惑。爲什麼在onCreate（）中查詢？當convertDatabase（SQLiteDatabase數據庫）將返回true？我的Android版本是2.2

Answer 1

有些情況下可以從日誌信息中檢索：

if (LOGD) Log.d(TAG, "converting database from an older format, but not onUpgrade"); 

如果有舊格式的數據庫，convertDatabase()副本的所有條目到新的使用copyFromCursor其中光標指向舊實例，然後刪除它。因此，如果該方法找到並轉換舊格式的數據庫實例，並返回true，否則返回false。

由於發射器實際上調用Launcher2很可能它試圖找到前任的痕跡。