Question

我正在使用此代码，但我得到了运行时异常。我做了所有必要的工作并努力消除此错误。但它对我不起作用。我正在使用DatabaseHandler。 java和AndroidSpinnerFromSQLiteActivity.java类，我的xml是activity_databse_handler.xml。

public class AndroidSpinnerFromSQLiteActivity extends Activity implements OnItemSelectedListener {
// Spinner element
Spinner spinner;

// Add button
utton btnAdd;

// Input text
EditText inputLabel; 



@Override
   public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_database_handler);
 // Spinner element
 spinner = (Spinner) findViewById(R.id.spinner);

  // add button
  btnAdd = (Button) findViewById(R.id.btn_add);

 // new label input field 
  inputLabel = (EditText) findViewById(R.id.input_label); 

 // Spinner click listener
   spinner.setOnItemSelectedListener(this);

 // Loading spinner data from database
 loadSpinnerData();

/**
* Add new label button click listener
* */
btnAdd.setOnClickListener(new View.OnClickListener() {

   @Override
   public void onClick(View arg0) {
    String label = inputLabel.getText().toString();

    if (label.trim().length() > 0) {
        // database handler
        DatabaseHandler db = new DatabaseHandler(getApplicationContext());

        // inserting new label into database
        db.insertLabel(label);

        // making input filed text to blank
        inputLabel.setText("");

        // Hiding the keyboard
        InputMethodManager imm = (InputMethodManager)   getSystemService(Context.INPUT_METHOD_SERVICE);
        imm.hideSoftInputFromWindow(inputLabel.getWindowToken(), 0);

        // loading spinner with newly added data
        loadSpinnerData();
    } else {
        Toast.makeText(getApplicationContext(), "Please enter label name",
                Toast.LENGTH_SHORT).show();
    }

   }
 });
  }

    /**
    * Function to load the spinner data from SQLite database
    * */
 public void loadSpinnerData() {
   // database handler
   DatabaseHandler db = new DatabaseHandler(getApplicationContext());

   // Spinner Drop down elements
   List<String> lables = db.getAllLabels();

   // Creating adapter for spinner
  ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,
    android.R.layout.simple_spinner_item, lables);

  // Drop down layout style - list view with radio button
  dataAdapter
    .setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

 // attaching data adapter to spinner
   spinner.setAdapter(dataAdapter);
}

@Override
public void onItemSelected(AdapterView<?> parent, View view, int position,
long id) {
 // On selecting a spinner item
 String label = parent.getItemAtPosition(position).toString();

   // Showing selected spinner item
    Toast.makeText(parent.getContext(), "You selected: " + label,
    Toast.LENGTH_LONG).show();

   }

  @Override
public void onNothingSelected(AdapterView<?> arg0) {
    // TODO Auto-generated method stub

    }

   }

=============================================== ============================================

    public class DatabaseHandler extends SQLiteOpenHelper {

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

      // Creating Tables
     @Override
     public void onCreate(SQLiteDatabase db) {
        try {
           // Category table create query
            String CREATE_CATEGORIES_TABLE = "CREATE TABLE " + TABLE_LABELS + "("+         KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT)";
           db.execSQL(CREATE_CATEGORIES_TABLE);
        }
        catch (Exception e) {
        // TODO: handle exception

        }
   }


// Upgrading database
 @Override 
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
  // Drop older table if existed
 db.execSQL("DROP TABLE IF EXISTS " + TABLE_LABELS);

   // Create tables again
  onCreate(db);
}

  /**
   * Inserting new lable into lables table
 * */

//数据库版本 private static int DATABASE_VERSION = 1;

// Database Name
   private static  String DATABASE_NAME = "spinnerExample";

//标签表名称 private static String TABLE_LABELS =“labels”;

// Labels Table Columns names
private static  String KEY_ID = "id";
private static  String KEY_NAME = "name";
 public void insertLabel(String label){
   SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_NAME, label);

      // Inserting Row
    db.insert(TABLE_LABELS, null, values);
  db.close(); // Closing database connection
            }






* Getting all labels
 * returns list of labels
   * */
        public List<String> getAllLabels(){
        List<String> labels = new ArrayList<String>();

     // Select All Query
       String selectQuery = "SELECT  * FROM " + TABLE_LABELS;

       SQLiteDatabase db = this.getReadableDatabase();
      Cursor cursor = db.rawQuery(selectQuery, null); 

        // looping through all rows and adding to list
          if (cursor.moveToFirst()) {
           do {
        labels.add(cursor.getString(1));
         } while (cursor.moveToNext());
        }

         // closing connection
          cursor.close();
      db.close();

         // returning lables
       return labels;
         }

}

=============================================== ============================================

   <!-- Label -->

  <!-- Input Text -->

<!-- Add Button -->

<!-- Select Label -->
  <TextView
   android:layout_width="fill_parent"
 android:layout_height="wrap_content"
  android:text="Select Label"
    android:padding="8dip" />

  <!-- Spinner Dropdown -->
   <Spinner
    android:id="@+id/spinner"
       android:layout_width="fill_parent"
  android:layout_height="wrap_content"
     android:prompt="@string/spinner_title"
   android:layout_marginTop="20dip"
   android:layout_marginLeft="8dip"
 android:layout_marginRight="8dip"
  />
    </LinearLayout>

Answer 1

您不希望数据库的应用程序上下文，您需要活动上下文，因此您的调用应该是：

DatabaseHandler db = new DatabaseHandler(this);

当我使用数据库时，无法实例化活动

1 个答案: