关于第五个问题我看了一下API,感觉有些东西浮出水面了,看来很多东西都藏在官方文档里啊。
public synchronized SQLiteDatabase getReadableDatabase ()
Since: API Level 1 Create and/or open a database. This will be the same object returned by getWritableDatabase() unless some problem, such as a full disk, requires the database to be opened read-only. In that case, a read-only database object will be returned. If the problem is fixed, a future call to getWritableDatabase() may succeed, in which case the read-only database object will be closed and the read/write object will be returned in the future.
Returns
a database object valid until getWritableDatabase() or close() is called.
Throws
SQLiteException if the database cannot be opened
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