Question

我正在尝试开发基于Google Notepad example的Android应用程序（当你下载zip文件时，有6个文件夹;我正在使用Notepadv3Solution项目。）

我想要做的是完全相同的应用程序，但有更多字段，如您的名字或您喜欢的地方。我的逻辑说我要复制样本项但更改名称。例如，在NotesDbAdapter.class上，当它写成：

public class NotesDbAdapter {
    public static final String KEY_TITLE = "title";
    public static final String KEY_BODY = "body";

我写道：

public class NotesDbAdapter {
    public static final String KEY_TITLE = "title";
    public static final String KEY_BODY = "body";
    public static final String kName = "name";
    public static final String kPlace = "place";
  ...

我在所有地方都说了这个问题，它说的是“标题”或“正文”，但它给了我错误（引起：android.database.sqlite.SQLiteException：无法降级数据库版本80到2 ）

所以，如果你不想下载这个例子，那么它就是：

Notepadv3.class：

package com.android.demo.notepad3;

import ...

public class Notepadv3 extends ListActivity {
    private static final int ACTIVITY_CREATE=0;
    private static final int ACTIVITY_EDIT=1;

    private static final int INSERT_ID = Menu.FIRST;
    private static final int DELETE_ID = Menu.FIRST + 1;

    private NotesDbAdapter mDbHelper;

    /** Called when the activity is first created. */
    @Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.notes_list);
    mDbHelper = new NotesDbAdapter(this);
    mDbHelper.open();
    fillData();
    registerForContextMenu(getListView());
}

private void fillData() {
    Cursor notesCursor = mDbHelper.fetchAllNotes();
    startManagingCursor(notesCursor);

    // Create an array to specify the fields we want to display in the list (only TITLE)
    String[] from = new String[]{NotesDbAdapter.KEY_TITLE};

    // and an array of the fields we want to bind those fields to (in this case just text1)
    int[] to = new int[]{R.id.text1};

    // Now create a simple cursor adapter and set it to display
    SimpleCursorAdapter notes = 
        new SimpleCursorAdapter(this, R.layout.notes_row, notesCursor, from, to);
    setListAdapter(notes);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    super.onCreateOptionsMenu(menu);
    menu.add(0, INSERT_ID, 0, R.string.menu_insert);
    return true;
}

@Override
public boolean onMenuItemSelected(int featureId, MenuItem item) {
    switch(item.getItemId()) {
        case INSERT_ID:
            createNote();
            return true;
    }

    return super.onMenuItemSelected(featureId, item);
}

@Override
public void onCreateContextMenu(ContextMenu menu, View v,
        ContextMenuInfo menuInfo) {
    super.onCreateContextMenu(menu, v, menuInfo);
    menu.add(0, DELETE_ID, 0, R.string.menu_delete);
}

@Override
public boolean onContextItemSelected(MenuItem item) {
    switch(item.getItemId()) {
        case DELETE_ID:
            AdapterContextMenuInfo info = (AdapterContextMenuInfo) item.getMenuInfo();
            mDbHelper.deleteNote(info.id);
            fillData();
            return true;
    }
    return super.onContextItemSelected(item);
}

private void createNote() {
    Intent i = new Intent(this, NoteEdit.class);
    startActivityForResult(i, ACTIVITY_CREATE);
}

@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
    super.onListItemClick(l, v, position, id);
    Intent i = new Intent(this, NoteEdit.class);
    i.putExtra(NotesDbAdapter.KEY_ROWID, id);
    startActivityForResult(i, ACTIVITY_EDIT);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
    super.onActivityResult(requestCode, resultCode, intent);
    fillData();
}
}

NotesDbAdapter.class：

package com.android.demo.notepad3;

import ...

public class NotesDbAdapter {

public static final String KEY_TITLE = "title";
public static final String KEY_BODY = "body";
public static final String KEY_ROWID = "_id";

private static final String TAG = "NotesDbAdapter";
private DatabaseHelper mDbHelper;
private SQLiteDatabase mDb;

/**
 * Database creation sql statement
 */
private static final String DATABASE_CREATE =
    "create table notes (_id integer primary key autoincrement, "
    + "title text not null, body text not null);";

private static final String DATABASE_NAME = "data";
private static final String DATABASE_TABLE = "notes";
private static final int DATABASE_VERSION = 2;

private final Context mCtx;

private static class DatabaseHelper extends SQLiteOpenHelper {

    DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        db.execSQL(DATABASE_CREATE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.w(TAG, "Upgrading database from version " + oldVersion + " to "
                + newVersion + ", which will destroy all old data");
        db.execSQL("DROP TABLE IF EXISTS notes");
        onCreate(db);
    }
}


public NotesDbAdapter(Context ctx) {
    this.mCtx = ctx;
}


public NotesDbAdapter open() throws SQLException {
    mDbHelper = new DatabaseHelper(mCtx);
    mDb = mDbHelper.getWritableDatabase();
    return this;
}

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

public long createNote(String title, String body) {
    ContentValues initialValues = new ContentValues();
    initialValues.put(KEY_TITLE, title);
    initialValues.put(KEY_BODY, body);

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


public boolean deleteNote(long rowId) {

    return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}

public Cursor fetchAllNotes() {

    return mDb.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_TITLE,
            KEY_BODY}, null, null, null, null, null);
}

public Cursor fetchNote(long rowId) throws SQLException {

    Cursor mCursor =

        mDb.query(true, DATABASE_TABLE, new String[] {KEY_ROWID,
                KEY_TITLE, KEY_BODY}, KEY_ROWID + "=" + rowId, null,
                null, null, null, null);
    if (mCursor != null) {
        mCursor.moveToFirst();
    }
    return mCursor;

}

public boolean updateNote(long rowId, String title, String body) {
    ContentValues args = new ContentValues();
    args.put(KEY_TITLE, title);
    args.put(KEY_BODY, body);

    return mDb.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
}
}

NoteEdit.class

package com.android.demo.notepad3;

import ...

public class NoteEdit extends Activity {

    private EditText mTitleText;
    private EditText mBodyText;
    private Long mRowId;
    private NotesDbAdapter mDbHelper;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    mDbHelper = new NotesDbAdapter(this);
    mDbHelper.open();

    setContentView(R.layout.note_edit);
    setTitle(R.string.edit_note);

    mTitleText = (EditText) findViewById(R.id.title);
    mBodyText = (EditText) findViewById(R.id.body);

    Button confirmButton = (Button) findViewById(R.id.confirm);

    mRowId = (savedInstanceState == null) ? null :
        (Long) savedInstanceState.getSerializable(NotesDbAdapter.KEY_ROWID);
    if (mRowId == null) {
        Bundle extras = getIntent().getExtras();
        mRowId = extras != null ? extras.getLong(NotesDbAdapter.KEY_ROWID)
                                : null;
    }

    populateFields();

    confirmButton.setOnClickListener(new View.OnClickListener() {

        public void onClick(View view) {
            setResult(RESULT_OK);
            finish();
        }

    });
}

private void populateFields() {
    if (mRowId != null) {
        Cursor note = mDbHelper.fetchNote(mRowId);
        startManagingCursor(note);
        mTitleText.setText(note.getString(
                note.getColumnIndexOrThrow(NotesDbAdapter.KEY_TITLE)));
        mBodyText.setText(note.getString(
                note.getColumnIndexOrThrow(NotesDbAdapter.KEY_BODY)));
    }
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    saveState();
    outState.putSerializable(NotesDbAdapter.KEY_ROWID, mRowId);
}

@Override
protected void onPause() {
    super.onPause();
    saveState();
}

@Override
protected void onResume() {
    super.onResume();
    populateFields();
}

private void saveState() {
    String title = mTitleText.getText().toString();
    String body = mBodyText.getText().toString();

    if (mRowId == null) {
        long id = mDbHelper.createNote(title, body);
        if (id > 0) {
            mRowId = id;
        }
    } else {
        mDbHelper.updateNote(mRowId, title, body);
    }
}

}

note_edit.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">

<LinearLayout android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <TextView android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:text="@string/title" />
    <EditText android:id="@+id/title" 
      android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:layout_weight="1"/>
</LinearLayout>

<TextView android:layout_width="wrap_content"
    android:layout_height="wrap_content" 
    android:text="@string/body" />
<EditText android:id="@+id/body" android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_weight="1"
    android:scrollbars="vertical" />

<Button android:id="@+id/confirm" 
  android:text="@string/confirm"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

</LinearLayout>

notes_list.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="wrap_content"
    android:layout_height="wrap_content">

<ListView android:id="@+id/android:list"
      android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
<TextView android:id="@+id/android:empty"
      android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/no_notes"/>
</LinearLayout>

notes_row.xml

<TextView android:id="@+id/text1" xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>

非常感谢!!

Answer 1

您复制的记事本应用程序中的数据库是使用版本号“80”制作的，您当前正在尝试使用版本号“2”。如果您尝试更改数据库，则数据库始终需要具有更高的版本号。

只需更改

private static final int DATABASE_VERSION = 2;

到

private static final int DATABASE_VERSION = 81;

将字段添加到Google记事本示例（SQLite）

1 个答案: