Question

MyDatabaseHelper helper = new MyDatabaseHelper(this);
SQLiteDatabase database = helper.getReadableDatabase();
String[] columns = {
        "_ID",
        "Title",
        "Subtitle"
};
Cursor cursor = database.query("MyTable", columns, null, null, null, null, null);

// Notice the position of these 2 lines. Will NOT crash if I move them to the bottom.
database.close();
helper.close();

String[] fromColumns = {
    "Title",
    "Subtitle"
};
int[] toViews = {
    R.id.list_view_item_text_view_title,
    R.id.list_view_item_text_view_subtitle
};
SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.list_view_item, cursor, fromColumns, toViews, 0);

ListView listView = (ListView) findViewById(R.id.activity_release_list_view);

// Crashed!
listView.setAdapter(adapter);

/**
 * Caused by: java.lang.IllegalStateException: Cannot perform this operation because the connection pool has been closed.
 * at android.database.sqlite.SQLiteConnectionPool.throwIfClosedLocked(SQLiteConnectionPool.java:962)
 * at android.database.sqlite.SQLiteConnectionPool.waitForConnection(SQLiteConnectionPool.java:599)
 * at android.database.sqlite.SQLiteConnectionPool.acquireConnection(SQLiteConnectionPool.java:348)
 * at android.database.sqlite.SQLiteSession.acquireConnection(SQLiteSession.java:894)
 * at android.database.sqlite.SQLiteSession.executeForCursorWindow(SQLiteSession.java:834)
 * at android.database.sqlite.SQLiteQuery.fillWindow(SQLiteQuery.java:62)
 * at android.database.sqlite.SQLiteCursor.fillWindow(SQLiteCursor.java:143)
 * at android.database.sqlite.SQLiteCursor.getCount(SQLiteCursor.java:133)
 * at android.support.v4.widget.CursorAdapter.getCount(CursorAdapter.java:202)
 * at android.widget.ListView.setAdapter(ListView.java:460)
 */

仅当我在listView.setAdapter(adapter)之后关闭数据库和数据库帮助程序时才有效。我关闭了数据库，因为我已经在Cursor中得到了结果集。 Cursor需要SimpleCursorAdapter，ListView需要{{1}}。它仍然崩溃。无论如何，ListView与数据库有什么关系？

Answer 1

适配器正在进行生命查询;它不能使用封闭的查询。

ListView从适配器读取足够的行以填充屏幕。只有在用户向下滚动后，ListView才会向适配器询问更多行。所以这意味着当发生这种情况时，查询仍然必须处于活动状态。

实质上，这意味着在关闭显示ListView的活动之前不要关闭数据库。

如果数据库连接关闭，android.widget.ListView.setAdapter（ListAdapter）会崩溃程序

1 个答案: