Question

运行 db.exec（q）方法时，它显示空对象引用。 db 是 SQLiteDatabase 类的对象。和exec（）是被覆盖的抽象方法。这是由SQLiteOpenHelper

扩展的DatabaseHelper类的代码

public class MyDbHelper extends SQLiteOpenHelper{

SQLiteDatabase db;
Context context;


MyDbHelper(Context context)
{
    super(context,"userDB",null,1);
    this.context = context;
    db = this.getWritableDatabase();
}


@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {


    String q = "create table user(uname text primary key,uage text,uphone text,bmi float)";
    db.execSQL(q);

}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

}


public void addData(String uname,String uage,String uphone,Double bmi)
{

    ContentValues cv = new ContentValues();
    cv.put("uname",uname);
    cv.put("uage",uage);
    cv.put("uphone",uphone);
    cv.put("bmi",bmi);
    long rid = db.insert("user",null,cv);

    if(rid<0)
    {
        Toast.makeText(context, "Insert Issue !!!!!", Toast.LENGTH_SHORT).show();
    }
    else
    {
        Toast.makeText(context, "Record Inserted !!!!!", Toast.LENGTH_SHORT).show();
    }
}

public String viewData()
{

    StringBuffer sb = new StringBuffer();
    Cursor c = db.query("user",null,null,null,null,null,null);
    c.moveToFirst();

    if(c.getCount() == 0 )
    {
        sb.append("No Records To Display");
    }
    else
    {
        do{
            String uname = c.getString(0);
            String uage = c.getString(1);
            String uphone = c.getString(2);
            float bmi = c.getFloat(3);
            sb.append("User : " +uname+ "\nAge : " +uage+ "\nPhone : " +uphone+ "\nBMI : " +bmi+ "\n\n---------------\n\n");


        }while (c.moveToNext());
    }

    return sb.toString();




}

}

Answer 1

替换此

 db.execSQL(q);

用这个

 sqLiteDatabase.execSQL(q);

首次安装应用时将触发

onCreate，您需要使用sqLiteDatabase引用来执行sql命令，并在实例化db时初始化MyDbHelper班级

.database.sqlite.SQLiteDatabase.execSQL（java.lang.String中）＆＃39;在null对象引用上

1 个答案: