cancellation和withdrawal 的区别

刚才在 CSDN 上看见有人问说在 Android SQLiteDatabase 里，query() 和 rawQuery() 方法的区别。对于这种问题，其实最好的办法就是参看源码，结果确实这样，通过源代码，很快就找到了问题的答案了。
咱们先看看 query() 是怎么实现的。
public Cursor query(String table, String[] columns, String selection,
String[] selectionArgs, String groupBy, String having, String orderBy) {
return query(false, table, columns, selection, selectionArgs, groupBy,
having, orderBy, null /* limit */);
}

public Cursor query(boolean distinct, String table, String[] columns,
String selection, String[] selectionArgs, String groupBy,
String having, String orderBy, String limit) {
return queryWithFactory(null, distinct, table, columns, selection, selectionArgs,
groupBy, having, orderBy, limit, null);
}

这几个方法都没有具体实现。
public Cursor queryWithFactory(CursorFactory cursorFactory,
boolean distinct, String table, String[] columns,
String selection, String[] selectionArgs, String groupBy,
String having, String orderBy, String limit, CancellationSignal cancellationSignal) {
acquireReference();
try {
String sql = SQLiteQueryBuilder.buildQueryString(
distinct, table, columns, selection, groupBy, having, orderBy, limit);

return rawQueryWithFactory(cursorFactory, sql, selectionArgs,
findEditTable(table), cancellationSignal);
} finally {
releaseReference();
}
}

最终调用的就是这个方法。
public Cursor rawQueryWithFactory(
CursorFactory cursorFactory, String sql, String[] selectionArgs,
String editTable, CancellationSignal cancellationSignal) {
acquireReference();
try {
SQLiteCursorDriver driver = new SQLiteDirectCursorDriver(this, sql, editTable,
cancellationSignal);
return driver.query(cursorFactory != null ? cursorFactory : mCursorFactory,
selectionArgs);
} finally {
releaseReference();
}
}

咱们再看看 rawQuery() 是怎么实现的。
public Cursor rawQuery(String sql, String[] selectionArgs) {
return rawQueryWithFactory(null, sql, selectionArgs, null, null);
}

还是这个方法。
public Cursor rawQueryWithFactory(
CursorFactory cursorFactory, String sql, String[] selectionArgs,
String editTable, CancellationSignal cancellationSignal) {
acquireReference();
try {
SQLiteCursorDriver driver = new SQLiteDirectCursorDriver(this, sql, editTable,
cancellationSignal);
return driver.query(cursorFactory != null ? cursorFactory : mCursorFactory,
selectionArgs);
} finally {
releaseReference();
}
}

可以看到，最后，调用的都是rawQueryWithFactory(CursorFactory,String,String[],String,CancellationSignal) 这个方法，你完全可以代码都不用看懂都可以找到答案。
回到问题上，这两个方法的区别在于，最终的 SQL 语句，谁来拼？query() 做的一件事就是帮你拼写 SQL 语句，而调用 rawQuery() 是你自己拼写好语句。我认为的差别仅次而已。
（转载）