Question

我正在尝试使用sqlite DB在我的Android应用程序中存储图像以及其他信息，但我收到此错误

06-20 12:00:51.411    4132-4132/braindottech.com.fishid E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: braindottech.com.fishid, PID: 4132
java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference
        at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:223)
        at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:163)
        at braindottech.com.fishid.PhotoDBMS.<init>(PhotoDBMS.java:65)
        at braindottech.com.fishid.CameraScan$6.onClick(UseSqliteDB.java:23)
        at android.view.View.performClick(View.java:5204)
        at android.view.View$PerformClick.run(View.java:21153)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:5417)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

这是我的＆＃34; UseSqliteDB.java＆＃34;代码：

public class UseSqliteDB extends Fragment {

  private Button saveResult;

  public UseSqliteDB(){}

  @Override
  public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); }

  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container, final Bundle savedInstanceState) {

      View v = inflater.inflate(R.layout.fragment_camera, container, false);

      context = this.getActivity();
      saveResult = (Button) v.findViewById(R.id.button_save_CameraPreview);

      saveResult.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v) {

            try {
                PhotoDBMS photoDBMS = new PhotoDBMS(getActivity());
                String nameImage = "IMAGE";
                Calendar calendar = Calendar.getInstance();
                nameImage += calendar.get(Calendar.DATE) + calendar.get(Calendar.HOUR) + calendar.get(Calendar.MINUTE) +
                        calendar.get(Calendar.SECOND) + calendar.get(Calendar.MILLISECOND);
                Boolean response = photoDBMS.insertData(nameImage, resultTV.getText().toString(), finalBitmap);
                if (!response) {
                    Toast.makeText(context, "Database entry failed!", Toast.LENGTH_LONG).show();
                } else {
                    Toast.makeText(context, "Database entry successful!", Toast.LENGTH_LONG).show();
                }

            }catch(Exception e){
               Log.d("HIP","E = "+e);
            }

        }
      });

      return v;
  }

}

PhotoDBMS.java

public class PhotoDBMS {

  private Context context;

  public PhotoDBMS(Context c){
      context = c;
  }

  public static abstract class DBMS_Constants implements BaseColumns {
      public static final String TABLE_NAME = "MY_COLLECTION";
      public static final String COLUMN_NAME_NAME = "Name";
      public static final String COLUMN_NAME_INFO = "Info";
      public static final String COLUMN_NAME_IMAGE = "Image";
  }

  private static final String TEXT_TYPE = " TEXT";
  private static final String COMMA_SEP = ",";
  private static final String BLOB = "BLOB";
  private static final String SQL_CREATE_TABLE = "CREATE TABLE " + DBMS_Constants.TABLE_NAME + " (" +
        DBMS_Constants._ID + " INTEGER PRIMARY KEY," +
        DBMS_Constants.COLUMN_NAME_NAME + TEXT_TYPE + COMMA_SEP +
        DBMS_Constants.COLUMN_NAME_INFO + TEXT_TYPE + COMMA_SEP +
        DBMS_Constants.COLUMN_NAME_IMAGE + BLOB + " )";

  private static final String SQL_DELETE_ENTRIES = "DROP TABLE IF EXISTS " + DBMS_Constants.TABLE_NAME;

  public class DbHelper extends SQLiteOpenHelper {
    // If you change the database schema, you must increment the database version.
      public static final int DATABASE_VERSION = 1;
      public static final String DATABASE_NAME = "FeedReader.db";

      public DbHelper(Context context) {
          super(context, DATABASE_NAME, null, DATABASE_VERSION);
      }
      public void onCreate(SQLiteDatabase db) {
          db.execSQL(SQL_CREATE_TABLE);
      }
      public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // This database is only a cache for online data, so its upgrade policy is
        // to simply to discard the data and start over
          db.execSQL(SQL_DELETE_ENTRIES);
          onCreate(db);
      }

      public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
          onUpgrade(db, oldVersion, newVersion);
      }

  }

  DbHelper dbHelper = new DbHelper(context);
  SQLiteDatabase collectionDB = dbHelper.getWritableDatabase();

  public boolean insertData(String name, String info, Bitmap bm){

      bitmapUtility utility = new bitmapUtility();
      byte[] image =  utility.getBytes(bm);
      ContentValues cv = new  ContentValues();
      cv.put(DBMS_Constants.COLUMN_NAME_NAME,    name);
      cv.put(DBMS_Constants.COLUMN_NAME_INFO,    info);
      cv.put(DBMS_Constants.COLUMN_NAME_IMAGE, image);
      return collectionDB.insert( DBMS_Constants.TABLE_NAME, null, cv ) > 0;

  }

  public boolean deleteData(String name){
      return collectionDB.delete(DBMS_Constants.TABLE_NAME, DBMS_Constants.COLUMN_NAME_NAME + " = " + name, null) > 0;
  }

}

我在UseSqliteDB.java中的try-catch部分遇到此错误。请帮我解决这个错误。提前谢谢！

Answer 1

问题是由于：

DbHelper dbHelper = new DbHelper(context);
SQLiteDatabase collectionDB = dbHelper.getWritableDatabase();

在类级而不是在任何方法中添加行。

创建一个方法并使用photoDBMS调用它来创建和获取数据库对象：

public void createDB(){
    DbHelper dbHelper = new DbHelper(context);
    SQLiteDatabase collectionDB = dbHelper.getWritableDatabase();
}

并在Button onClick方法中调用它：

PhotoDBMS photoDBMS = new PhotoDBMS(getActivity());
photoDBMS.createDB();

或者在PhotoDBMS类构造函数

中移动这两行

Answer 2

试试这个，

将您的PhotoDBMS课程改为

public class DbHelper extends SQLiteOpenHelper {
    public static final String TABLE_NAME = "MY_COLLECTION";
    public static final String COLUMN_NAME_NAME = "Name";
    public static final String COLUMN_NAME_INFO = "Info";
    public static final String COLUMN_NAME_IMAGE = "Image";
    private static final String _ID = "id";

    private static final String TEXT_TYPE = " TEXT";
    private static final String COMMA_SEP = ",";
    private static final String BLOB = "BLOB";


    private static final String SQL_CREATE_TABLE = "CREATE TABLE " + TABLE_NAME + " (" +
            _ID + " INTEGER PRIMARY KEY," +
            COLUMN_NAME_NAME + TEXT_TYPE + COMMA_SEP +
            COLUMN_NAME_INFO + TEXT_TYPE + COMMA_SEP +
            COLUMN_NAME_IMAGE + BLOB + " )";

    private static final String SQL_DELETE_ENTRIES = "DROP TABLE IF EXISTS " + TABLE_NAME;

        // If you change the database schema, you must increment the database version.
        public static final int DATABASE_VERSION = 1;
        public static final String DATABASE_NAME = "FeedReader.db";

    public DbHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(SQL_CREATE_TABLE);
    }
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // This database is only a cache for online data, so its upgrade policy is
        // to simply to discard the data and start over
        db.execSQL(SQL_DELETE_ENTRIES);
        onCreate(db);
    }

    public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        onUpgrade(db, oldVersion, newVersion);
    }

    public boolean insertData(String name, String info, Bitmap bm){
        SQLiteDatabase sqLiteDatabase = getWritableDatabase();
        bitmapUtility utility = new bitmapUtility();
        byte[] image =  utility.getBytes(bm);
        ContentValues cv = new  ContentValues();
        cv.put(COLUMN_NAME_NAME,    name);
        cv.put(COLUMN_NAME_INFO,    info);
        cv.put(COLUMN_NAME_IMAGE, image);
        return sqLiteDatabase.insert( TABLE_NAME, null, cv ) > 0;

    }

    public boolean deleteData(String name){
        SQLiteDatabase sqLiteDatabase = getWritableDatabase();
        return sqLiteDatabase.delete(TABLE_NAME, COLUMN_NAME_NAME + " = " + name, null) > 0;
    }

}

call

    DbHelper dbHelper = new DbHelper(getActivity());
    dbHelper.insertData(nameImage, resultTV.getText().toString(), finalBitmap);

Sqlite在android中给出NullPointerException错误

2 个答案: