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首先，我是我正在学习的 android 的新开发人员，所以请多多包涵。我正在制作一个与书籍章节相关的应用程序并显示其内容，我从数据库中填充了工作列表视图，但面临一些错误：-

  1. 在离开应用程序时，我强制关闭查看日志猫。

  2. 在列表视图中，我正在将新数据附加到数据库中。我希望它只有一次。因为章节名称对于一本书来说是不变的

  3. 单击章节时，应打开选定的章节列表。

请让我知道如何纠正它们

主要活动

public class MainActivity extends Activity {

    DBADChapter myDb;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        openDB();
        registerListClickCallback();

    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        closeDB();
        myDb.deleteAll();
    }

    private void openDB() {
        myDb = new DBADChapter(this);
        myDb.open();
        myDb.insertRow(999, "TITLE 1");
        myDb.insertRow(991, "TITLE 2");
        myDb.insertRow(992, "TITLE 3");
        myDb.insertRow(993, "TITLE 4");
        populatelistviewfromDB();
    }

    private void closeDB() {
        myDb.close();
        myDb.deleteAll();

    }

    public void onClick_AddRecord(View v) {

    }

    private void populatelistviewfromDB() {
        Cursor cursor = myDb.getAllRows();
        startManagingCursor(cursor);

        String[] fromFieldNames = new String[] { DBADChapter.KEY_CHEPTERNUM,
                DBADChapter.KEY_CHAPTERHEADING };
        int[] toViewIds = new int[] { R.id.tvchapterno, R.id.tvchapter };
        SimpleCursorAdapter myCursorAdapter = new SimpleCursorAdapter(this,
                R.layout.item_view, cursor, fromFieldNames, toViewIds);

        ListView myList = (ListView) findViewById(R.id.listchapter);
        myList.setAdapter(myCursorAdapter);

    }

    private void registerListClickCallback() {

        ListView myList = (ListView) findViewById(R.id.listchapter);
        myList.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View viewClicked,
                    int position, long idInDB) {

                Cursor cursor = myDb.getRow(idInDB);
                if (cursor.moveToFirst()) {

                }
                cursor.close();

            }
        });
    }

    @Override
    protected void onPause() {

        super.onPause();
        closeDB();
        myDb.deleteAll();
    }

}

数据库

public class DBADChapter2 {

    private static final String TAG = "DBAdapter";

    public static final String KEY_ROWID = "_id";
    public static final int COL_ROWID = 0;

    public static final String KEY_CHEPTERNUM = "chapternum";
    public static final String KEY_CHAPTERHEADING = "chapterheading";

    public static final int COL_CHEPTERNUM = 1;
    public static final int COL_CHAPTERHEADING = 2;

    public static final String[] ALL_KEYS = new String[] { KEY_ROWID,
            KEY_CHEPTERNUM, KEY_CHAPTERHEADING };

    public static final String DATABASE_NAME = "MyDb";
    public static final String DATABASE_TABLE = "chapters";

    public static final int DATABASE_VERSION = 1;

    private static final String DATABASE_CREATE_SQL = "create table "
            + DATABASE_TABLE + " (" + KEY_ROWID
            + " integer primary key autoincrement, "

            + KEY_CHEPTERNUM + " integer not null, " + KEY_CHAPTERHEADING
            + " string not null"

            + ");";

    private final Context context;

    private DatabaseHelperChapter myDBHelper;
    private SQLiteDatabase db;

    public DBADChapter2(Context ctx) {
        this.context = ctx;
        myDBHelper = new DatabaseHelperChapter(context);
    }

    public DBADChapter2 open() {
        db = myDBHelper.getWritableDatabase();
        return this;
    }

    public void close() {
        myDBHelper.close();
    }

    public long insertRow(int number, String chapterheadings) {

        ContentValues initialValues = new ContentValues();
        initialValues.put(KEY_CHEPTERNUM, number);
        initialValues.put(KEY_CHAPTERHEADING, chapterheadings);

        return db.insert(DATABASE_TABLE, null, initialValues);
    }

    public boolean deleteRow(long rowId) {
        String where = KEY_ROWID + "=" + rowId;
        return db.delete(DATABASE_TABLE, where, null) != 0;
    }

    public void deleteAll() {
        Cursor c = getAllRows();
        long rowId = c.getColumnIndexOrThrow(KEY_ROWID);
        if (c.moveToFirst()) {
            do {
                deleteRow(c.getLong((int) rowId));
            } while (c.moveToNext());
        }
        c.close();
    }

    public Cursor getAllRows() {
        String where = null;
        Cursor c = db.query(true, DATABASE_TABLE, ALL_KEYS, where, null, null,
                null, null, null);
        if (c != null) {
            c.moveToFirst();
        }
        return c;
    }

    public Cursor getRow(long rowId) {
        String where = KEY_ROWID + "=" + rowId;
        Cursor c = db.query(true, DATABASE_TABLE, ALL_KEYS, where, null, null,
                null, null, null);
        if (c != null) {
            c.moveToFirst();
        }
        return c;
    }

    private static class DatabaseHelperChapter extends SQLiteOpenHelper {
        DatabaseHelperChapter(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase _db) {
            _db.execSQL(DATABASE_CREATE_SQL);
        }

        @Override
        public void onUpgrade(SQLiteDatabase _db, int oldVersion, int newVersion) {
            Log.w(TAG, "Upgrading application's database from version "
                    + oldVersion + " to " + newVersion
                    + ", which will destroy all old data!");

            _db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);

            onCreate(_db);
        }
    }
}

日志猫

10-06 18:52:30.822: E/AndroidRuntime(564): FATAL EXCEPTION: main
10-06 18:52:30.822: E/AndroidRuntime(564): java.lang.RuntimeException: Unable to pause activity {com.bookz.bookz1/com.bookz.bookz1.MainActivity}: java.lang.IllegalStateException: database not open
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.app.ActivityThread.performPauseActivity(ActivityThread.java:2354)
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.app.ActivityThread.performPauseActivity(ActivityThread.java:2311)
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:2291)
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.app.ActivityThread.access$1700(ActivityThread.java:117)
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:942)
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.os.Handler.dispatchMessage(Handler.java:99)
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.os.Looper.loop(Looper.java:123)
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.app.ActivityThread.main(ActivityThread.java:3683)
10-06 18:52:30.822: E/AndroidRuntime(564):  at java.lang.reflect.Method.invokeNative(Native Method)
10-06 18:52:30.822: E/AndroidRuntime(564):  at java.lang.reflect.Method.invoke(Method.java:507)
10-06 18:52:30.822: E/AndroidRuntime(564):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
10-06 18:52:30.822: E/AndroidRuntime(564):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
10-06 18:52:30.822: E/AndroidRuntime(564):  at dalvik.system.NativeStart.main(Native Method)
10-06 18:52:30.822: E/AndroidRuntime(564): Caused by: java.lang.IllegalStateException: database not open
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.database.sqlite.SQLiteDatabase.queryWithFactory(SQLiteDatabase.java:1230)
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.database.sqlite.SQLiteDatabase.query(SQLiteDatabase.java:1189)
10-06 18:52:30.822: E/AndroidRuntime(564):  at com.bookz.bookz1.DBADChapter.getAllRows(DBADChapter.java:130)
10-06 18:52:30.822: E/AndroidRuntime(564):  at com.bookz.bookz1.DBADChapter.deleteAll(DBADChapter.java:117)
10-06 18:52:30.822: E/AndroidRuntime(564):  at com.bookz.bookz1.MainActivity.closeDB(MainActivity.java:53)
10-06 18:52:30.822: E/AndroidRuntime(564):  at com.bookz.bookz1.MainActivity.onPause(MainActivity.java:79)
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.app.Activity.performPause(Activity.java:3851)
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.app.Instrumentation.callActivityOnPause(Instrumentation.java:1191)
10-06 18:52:30.822: E/AndroidRuntime(564):  at android.app.ActivityThread.performPauseActivity(ActivityThread.java:2341)
10-06 18:52:30.822: E/AndroidRuntime(564):  ... 12 more
4

1 回答 1

1

在您的 onPause() 方法中，您说：

     super.onPause();
    closeDB();
    myDb.deleteAll();

而且您的 closeDB() 还会执行以下操作：

     myDb.close();
    myDb.deleteAll();

因此，您的代码中的错误之一是您无缘无故地调用了两次 deleteAll()。

其次，你为什么要先调用 closeDB 然后再调用 deleteAll ？简单的逻辑说，一旦你完成了所有的工作，你就关闭了你的数据库。您登录 cat 说错误是“数据库未打开”，因此您显然已经关闭了数据库，但您尝试使用它做更多的工作。

尝试切换 deleteAll 的位置并关闭，这应该可以解决问题。

于 2013-10-06T14:19:13.447 回答