Question

在向我的数据库添加数据时，我有一个nullPointerExeption。通常我会认为我忘记了一个字符串，但EditTexts都填充了数据。我发现我的DBHelper实例没有创建。但是我不知道我必须使用哪个命令来创建一个。

（this）和getActivity（）/ getContext（）都不起作用......

这是我的片段代码：

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
import android.widget.Button;


public class AddDataFragment extends Fragment {
    DbHelper mydb;

    Button buttonadd;
    Button buttondelete;

    private EditText inputProduct;
    private EditText inputLabel;
    private EditText inputSerial;
    private EditText inputMac;
    private EditText inputDaaId;
    private EditText inputBill;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_add_data, container, false);
        inputProduct = (EditText) view.findViewById(R.id.editText_product);
        inputLabel = (EditText) view.findViewById(R.id.editText_label);
        inputSerial = (EditText) view.findViewById(R.id.editText_serial);
        inputMac = (EditText) view.findViewById(R.id.editText_mac);
        inputDaaId = (EditText) view.findViewById(R.id.editText_daa_id);
        inputBill = (EditText) view.findViewById(R.id.editText_bill);
        buttonadd = (Button) view.findViewById(R.id.button_add_addData);
        buttondelete = (Button) view.findViewById(R.id.button_delete_addData);

        buttonadd.setEnabled(true);
        buttondelete.setEnabled(true);

        mydb = new DbHelper(getActivity());//////////////////////////////////////////////////////////////////////////////////////


        buttonadd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                String product = inputProduct.getText().toString();
                String label = inputLabel.getText().toString();
                String serial = inputSerial.getText().toString();
                String mac = inputMac.getText().toString();
                String daaid = inputDaaId.getText().toString();
                String bill = inputBill.getText().toString();

                mydb.insertData(product, label, serial, mac, daaid, bill);

            }

        });

        return view;
    }

}

我的DbHelper课可能有问题。但我找不到......

import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DbHelper extends SQLiteOpenHelper{

    public static final String DB_NAME = "DAAInv.db";
    public static final int DB_VERSION = 1;

    public static final String TABLE_LISTELEMENT = "listelement";
    public static final String COLUMN_ID = "id";
    public static final String COLUMN_PRODUCT = "product";
    public static final String COLUMN_LABEL = "label";
    public static final String COLUMN_SERIAL = "serial";
    public static final String COLUMN_MAC = "mac";
    public static final String COLUMN_DAAID = "daaid";
    public static final String COLUMN_BILL = "bill";

    public static final String SQL_CREATE =
            "create table " + TABLE_LISTELEMENT + "(" +
                    COLUMN_ID + " integer primary key autoincrement, " +
                    COLUMN_PRODUCT + " text not null, " +
                    COLUMN_LABEL + " text not null, " +
                    COLUMN_SERIAL + " text not null, " +
                    COLUMN_MAC + " text not null, " +
                    COLUMN_DAAID + " text not null, " +
                    COLUMN_BILL + " text not null";

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(SQL_CREATE);                             //Datenbanktable erstellen

        ContentValues contentValues = new ContentValues();

        contentValues.put("product", "PC");
        contentValues.put("label", "WSN-1234");
        contentValues.put("serial", "R4HSU74H");
        contentValues.put("mac", "45:S8:LK:0L:5K");
        contentValues.put("daaid", "145789");
        contentValues.put("bill", "15.19.2015");
        db.insert(TABLE_LISTELEMENT, null, contentValues);

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }

    public DbHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    public boolean insertData(String product, String label, String serial, String mac, String daaid, String bill) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues contentValues = new ContentValues();

        contentValues.put("product", product);
        contentValues.put("label", label);
        contentValues.put("serial", serial);
        contentValues.put("mac", mac);
        contentValues.put("daaid", daaid);
        contentValues.put("bill", bill);
        db.insert(TABLE_LISTELEMENT, null, contentValues);
        return true;
    }
}

Answer 1

您忘记创建db帮助程序的实例。

 mydb.insertData(product, label, serial, mac, daaid, bill);

mydb为空

如何在Fragment中创建DBHelper的实例

1 个答案: