android的数据库帮助类getWritableDatabase，空指针错误

2018-04-03 11:26:48 1.6k 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

正交试验实战指南：从PICT工具到混合水平表应用本文详细介绍了正交试验法在测试设计中的实战应用，从基础概念到PICT工具的高级使用技巧。通过混合水平表设计和工程化实践案例，帮助测试工程师高效解决参数组合爆炸问题，提升测试覆盖率与效率。特别适合兼容性测试和复杂系统验证场景。阅读详情

DBHelp



public class DbHelper extends SQLiteOpenHelper {



    private final static String DB_NAME = "HKC";



    public DbHelper(Context context) {

        super(context, DB_NAME, null, 1);

    }



    @Override

    public void onCreate(SQLiteDatabase db) {

        //创建了一个名为person的表

        String sql = "CREATE TABLE product_info(_id INTEGER PRIMARY KEY AUTOINCREMENT," +

                "iccid varchar(10)," +

                "name varchar(50)," +

                "directions varchar(100)," +

                "type varchar(1)," +

                "price varchar(10)," +

                "old_price varchar(10))";

        db.execSQL(sql);

        Log.d("SQLiteDatabaseTest", sql);

    }



    @Override

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



    }

}

MainActivity 代码



public class MainActivity extends Activity {



    private static final String TAG = "MainActivity";



    DbHelper dbHelper=new DbHelper(this);

    SQLiteDatabase db=dbHelper.getWritableDatabase();





    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

    }



    public void onClick(View view) {

        switch (view.getId()) {

            case R.id.insert:

                break;

            case R.id.select:

                break;

        }

    }

}

异常
Caused by: 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

...全文