Android - 在textView中登錄後顯示來自sqlite數據庫的用戶名

Question

我是開發android應用程序的新手，我想在導航抽屜中成功登錄後顯示用戶名。我的問題是如何從sqlite數據庫中只提取用戶名並將其顯示在textView中。 See the picture

這是我的代碼，到目前爲止，我DatabaseHelper

public class DatabaseHelper extends SQLiteOpenHelper{ 

public static final String DATABASE_NAME = "Users.db"; 
public static final String TABLE_NAME = "users_table"; 
private static final int DATABASE_VERSION = 1; 

private static final String KEY_ID = "id"; 
private static final String KEY_NAME = "username"; 
private static final String KEY_PASS = "password"; 

SQLiteDatabase db; 

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

@Override 
public void onCreate(SQLiteDatabase db) { 
    db.execSQL("CREATE TABLE "+TABLE_NAME+" (_id INTEGER PRIMARY KEY AUTOINCREMENT, username TEXT, password TEXT);"); 
    db.execSQL("INSERT INTO " + TABLE_NAME + " VALUES (null, 'admin', '12345');"); 

} 

public String searchPass(String uname){ 
    db = this.getReadableDatabase(); 
    String query = "SELECT username, password FROM "+TABLE_NAME; 
    Cursor cursor = db.rawQuery(query, null); 
    String a, b; 
    b = "not found"; 
    if(cursor.moveToFirst()){ 
     do{ 
      a = cursor.getString(0); 
      if(a.equals(uname)){ 
       b = cursor.getString(1); 
       break; 
      } 
     }while(cursor.moveToNext()); 
    } 
    return b; 
} 

@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
    db.execSQL("DROP TABLE IF EXISTS "+TABLE_NAME); 
    onCreate(db); 
} } 

和這裏就是我想要顯示我的用戶名

public class MenuHome extends AppCompatActivity 
    implements NavigationView.OnNavigationItemSelectedListener { 

public static final String PREFS_NAME = "LoginPrefs"; 
DatabaseHelper helper = new DatabaseHelper(this); 

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

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 

    //set the fragment initially 
    HomeFragment fragment = new HomeFragment(); 
    setTitle(R.string.ttl_home); 
    FragmentTransaction fragmentTransaction = 
      getSupportFragmentManager().beginTransaction(); 
    fragmentTransaction.replace(R.id.fragment_container, fragment); 
    fragmentTransaction.commit(); 

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
      this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close); 
    drawer.setDrawerListener(toggle); 
    toggle.syncState(); 

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view); 
    navigationView.setNavigationItemSelectedListener(this); 

} 

@Override 
public void onBackPressed() { 
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
    if (drawer.isDrawerOpen(GravityCompat.START)) { 
     drawer.closeDrawer(GravityCompat.START); 
    } else { 
     super.onBackPressed(); 
    } 
} 

/*@Override    //Right Options Menu 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.menu_home, menu); 
    return true; 
}*/ 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 
     return false; 
    } 

    return super.onOptionsItemSelected(item); 
} 

@SuppressWarnings("StatementWithEmptyBody") 
@Override 
public boolean onNavigationItemSelected(MenuItem item) { 
    // Handle navigation view item clicks here. 
    int id = item.getItemId(); 

    if (id == R.id.nav_home) { 
     HomeFragment fragment = new HomeFragment(); 
     setTitle(R.string.ttl_home); 
     android.support.v4.app.FragmentTransaction fragmentTransaction = 
       getSupportFragmentManager().beginTransaction(); 
     fragmentTransaction.replace(R.id.fragment_container, fragment); 
     fragmentTransaction.commit(); 

    } else if (id == R.id.nav_inv) { 
     InventoryFragment fragment = new InventoryFragment(); 
     setTitle(R.string.ttl_inventory); 
     android.support.v4.app.FragmentTransaction fragmentTransaction = 
       getSupportFragmentManager().beginTransaction(); 
     fragmentTransaction.replace(R.id.fragment_container, fragment); 
     fragmentTransaction.commit(); 

    } else if (id == R.id.nav_prod) { 
     ProductFragment fragment = new ProductFragment(); 
     setTitle(R.string.ttl_products); 
     android.support.v4.app.FragmentTransaction fragmentTransaction = 
       getSupportFragmentManager().beginTransaction(); 
     fragmentTransaction.replace(R.id.fragment_container, fragment); 
     fragmentTransaction.commit(); 

    } else if (id == R.id.nav_clients) { 
     ClientsFragment fragment = new ClientsFragment(); 
     setTitle(R.string.ttl_clients); 
     android.support.v4.app.FragmentTransaction fragmentTransaction = 
       getSupportFragmentManager().beginTransaction(); 
     fragmentTransaction.replace(R.id.fragment_container, fragment); 
     fragmentTransaction.commit(); 

    } else if (id == R.id.nav_stat) { 
     StatsFragment fragment = new StatsFragment(); 
     setTitle(R.string.ttl_stat); 
     android.support.v4.app.FragmentTransaction fragmentTransaction = 
       getSupportFragmentManager().beginTransaction(); 
     fragmentTransaction.replace(R.id.fragment_container, fragment); 
     fragmentTransaction.commit(); 

    } else if (id == R.id.nav_prof) { 
     ProfileFragment fragment = new ProfileFragment(); 
     setTitle(R.string.ttl_prof); 
     android.support.v4.app.FragmentTransaction fragmentTransaction = 
       getSupportFragmentManager().beginTransaction(); 
     fragmentTransaction.replace(R.id.fragment_container, fragment); 
     fragmentTransaction.commit(); 

    } else if (id == R.id.nav_about) { 
     AboutFragment fragment = new AboutFragment(); 
     setTitle(R.string.ttl_about); 
     android.support.v4.app.FragmentTransaction fragmentTransaction = 
       getSupportFragmentManager().beginTransaction(); 
     fragmentTransaction.replace(R.id.fragment_container, fragment); 
     fragmentTransaction.commit(); 

    } else if (id == R.id.nav_logout) { 
     SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0); 
     SharedPreferences.Editor editor = settings.edit(); 
     editor.remove("logged"); 
     editor.commit(); 
     Intent intent = new Intent(MenuHome.this, MainActivity.class); 
     startActivity(intent); 
     finish(); 
    } 

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
    drawer.closeDrawer(GravityCompat.START); 
    return true; 
} } 

Answer 1

我會保存用戶名sharedpreferences，因爲應用程序將只一個用戶，你不需要只保存一個入口到你的數據庫。但是如果你堅持從數據庫中獲取它，那麼將這個函數添加到你的DatabaseHelper中。

public String getUsername() throws SQLException { 
        String username = ""; 
        Cursor cursor = this.getReadableDatabase().query(
                TABLE_NAME, new String[] { KEY_NAME }, 
                null, null, null, null, null);      
        if (cursor.moveToFirst()) { 
         do { 
          username = cursor.getString(0); 
         } while (cursor.moveToNext()); 
        } 
        cursor.close(); 

        return username; 
    } 

，以後你可以使用這個代碼在你的抽屜活動獲取用戶名：

textView.setText(helper.getUsername()); 

附：你應該真的重構你的代碼。並使用SharedPreferences而不是SQLite來存儲單個值。 SQLite旨在存儲海量數據容器，如緩存列表數據等。