ContentResolver 客户端应用无法从 ContentProvider 中找到 table

Question

无法真正找到这个特定案例的答案。我正在尝试从我的 contentprovider 应用程序的现有数据库中实现对所有行的非常简单的提取，并在列表视图中填充这些行。

我的客户端收到 classic 错误

android.database.sqlite.SQLiteException: no such table: names (code 1): , while compiling: SELECT * FROM names
            at android.database.DatabaseUtils.readExceptionFromParcel(DatabaseUtils.java:181)
            at android.database.DatabaseUtils.readExceptionFromParcel(DatabaseUtils.java:137)
            at android.content.ContentProviderProxy.query(ContentProviderNative.java:421)
            at android.content.ContentResolver.query(ContentResolver.java:478)
            at android.content.CursorLoader.loadInBackground(CursorLoader.java:64)
            at com.example.user.myclient.MainActivity.onCreate(MainActivity.java:25)

这是MyClient的main中的简单代码：

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

        Uri uri = Uri.parse("content://map524.myfriends");
        Cursor c;
        CursorLoader cl = new CursorLoader(this, uri, null, null, null, null);
        c = cl.loadInBackground();

        String[] columns = new String[] {
            "Id", "name", "phone", "email"
        };

        int[] views = new int[] {
          R.id.namesId, R.id.names, R.id.phone, R.id.email
        };
        SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.activity_main, c, columns, views);

        ListView lv = (ListView)findViewById(R.id.listView);
        lv.setAdapter(adapter);
    }

内容提供者的 class 只是执行一个 "SELECT * FROM names"，这是数据库中现有的 table。此查询在包含数据库文件作为资产的本地应用程序上完美运行。 当我继续运行内容提供商应用程序，然后尝试运行我的内容 resolver/client 应用程序在同一个 AVD 上时，会发生错误：

// MyDBProvider class
public class FriendsProvider extends ContentProvider {
    MySQLiteHelper dbHelper;

// ... Required blank methods all exist of course, but not implemented
 @Override
    public boolean onCreate() {
        // TODO: Implement this to initialize your content provider on startup.

        dbHelper = new MySQLiteHelper(getContext());
        return false;
    }
@Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
        // TODO: Implement this to handle query requests from clients.
        SQLiteDatabase db = dbHelper.getReadableDatabase();

        return db.query("names", projection, selection, selectionArgs, null, null, sortOrder);
    }

这段代码在 contentProvider 的本地应用程序中运行良好：

public class MySQLiteHelper extends SQLiteOpenHelper {
    public static final String TABLE_NAMES = "names";
    public static final String COLUMN_ID = "_id";
    public static final String COLUMN_NAME = "name";

    private static final String DATABASE_NAME = "names.db";
    private static String DB_PATH = "";
    private static final int DATABASE_VERSION = 3;
    private static final String DATABASE_CREATE = "CREATE TABLE names (_id integer PRIMARY KEY, name text, phone text, email text);";
    private final Context mContext;
    private SQLiteDatabase mDataBase;

    public MySQLiteHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        DB_PATH = context.getDatabasePath(DATABASE_NAME).getPath();

        this.mContext = context;
    }

    public void createDataBase() throws IOException {
        //If database not exists copy it from the assets
        boolean mDataBaseExist = checkDataBase();
        if(!mDataBaseExist)
        {
            this.getReadableDatabase();
            try
            {
                //Copy the database from assets
                copyDataBase();
                Log.e("MySQLiteHelper", "createDatabase database created");
            }
            catch (IOException mIOException)
            {
                throw new Error("ErrorCopyingDataBase");
            }
        }
    }

    private boolean checkDataBase() {
        File dbFile = new File(DB_PATH + DATABASE_NAME);
        //Log.v("dbFile", dbFile + "   "+ dbFile.exists());
        return dbFile.exists();
    }

    private void copyDataBase() throws IOException
    {
        InputStream mInput = mContext.getAssets().open(DATABASE_NAME);
        String outFileName = DB_PATH + DATABASE_NAME;
        OutputStream mOutput = new FileOutputStream(outFileName);
        byte[] mBuffer = new byte[1024];
        int mLength;
        while ((mLength = mInput.read(mBuffer))>0)
        {
            mOutput.write(mBuffer, 0, mLength);
        }
        mOutput.flush();
        mOutput.close();
        mInput.close();
    }

    public boolean openDataBase() throws SQLException
    {
        String mPath = DB_PATH + DATABASE_NAME;
        mDataBase = SQLiteDatabase.openDatabase(mPath, null, SQLiteDatabase.CREATE_IF_NECESSARY);
        return mDataBase != null;
    }

    @Override
    public void onCreate(SQLiteDatabase database) {
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    }

    public Cursor fetchRows() {
        String query = "SELECT * FROM " + TABLE_NAMES;
        Cursor cursor = mDataBase.rawQuery(query, null);
        return cursor;
    }

    @Override
    public synchronized void close()
    {
        if(mDataBase != null)
            mDataBase.close();
        super.close();
    }

一如既往地提前致谢。 }

Answer 1

显然这里的问题是我的内容提供程序逻辑最终尝试直接访问 SQLiteHelper 实例，而不是使用处理它的数据访问 Object/Database 适配器 class 逻辑。我的理解是，在这种情况下，尝试直接使用 SQLiteHelper 实例实现原始查询是试图从文件结构中没有任何 table 的数据库中查询 table。

我的新工作逻辑是这样的：

// In the provider class instance
NamesDataSource dbHelper;

 @Override
    public boolean onCreate() {
        // TODO: Implement this to initialize your content provider on startup.
        dbHelper = new NamesDataSource(getContext());
        try {
            dbHelper.open();
        }
        catch (SQLException se) {
            se.printStackTrace();
        }
        return false;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
        // TODO: Implement this to handle query requests from clients.
        //return db.query("names", projection, selection, selectionArgs, null, null,  sortOrder);
        return dbHelper.getRowsCursor();
    }
// ... rest of blank required implementation methods
}

数据访问Object/Database适配器Class:

public class NamesDataSource {
    private MySQLiteHelper dbHelper;

public NamesDataSource(Context context) {
        dbHelper = new MySQLiteHelper(context);
    }

public void open() throws SQLException {
        try {
            dbHelper.createDataBase();
        }
        catch (Exception ioe) {
            throw new Error("Unable to create database");
        }
        try {
            dbHelper.openDataBase();
        }
        catch(Exception se){
            se.printStackTrace();
        }
    }

public Cursor getRowsCursor() {
        return dbHelper.fetchRows();
    }
}

SQLiteHelper class 没有改变它的逻辑。客户端应用程序代码现在使用此逻辑来检索查询数据：

public class MainActivity extends Activity {
    Uri uri = Uri.parse("content://map524.myfriends");

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d("CLIENT", "Starting");
        fetchAll();
    }

public void fetchAll() {
        Cursor c = getContentResolver().query(uri, null,null,null,null);

        String[] columns = new String[] {
                "_id", "name", "phone", "email"
        };

        int[] views = new int[] {
                R.id.namesId, R.id.names, R.id.phone, R.id.email
        };

        SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, R.layout.activity_main, c, columns, views);

        ListView lv = (ListView)findViewById(R.id.listView);
        lv.setAdapter(adapter);
    }
}

ContentResolver 客户端应用无法从 ContentProvider 中找到 table

ContentResolver Client App cannot find table from ContentProvider

android

android-contentprovider

android-sqlite