Question

这是数据库文件：

   public class MyDBHandler extends SQLiteOpenHelper {
    public static final int DATABASE_VERSION=1;
    public static final String DATABASE_NAME="mydetails.db";
    public static final String TABLE_MYDETAIL="mydetails";
    public static final String COLUMN_NAME="_name";
    public static final String COLUMN_ROLLNUMBER="_rollNumber";
    public static final String COLUMN_MARKS="_marks";
    public static final String COLUMN_ID="_id";

    public MyDBHandler(Context context,String name, SQLiteDatabase.CursorFactory cursorFactory,int version){
        super(context,DATABASE_NAME,cursorFactory,DATABASE_VERSION);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        String query ="CREATE TABLE "+TABLE_MYDETAIL+"("+COLUMN_ID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+COLUMN_ROLLNUMBER+" INTEGER, "+ COLUMN_NAME+" TEXT, "+COLUMN_MARKS +" INTEGER"+");";
        Log.d("query",query);
        db.execSQL(query);

    }
    public void addMyDetail(MyDetails myDetails){
        ContentValues values= new ContentValues();
        values.put(COLUMN_ROLLNUMBER,myDetails.get_rollNumber());
        values.put(COLUMN_NAME,myDetails.get_name());
        values.put(COLUMN_MARKS,myDetails.get_marks());
        SQLiteDatabase db = getReadableDatabase();
        long id= db.insert(TABLE_MYDETAIL, null, values);
        Log.d("id", "addMyDetail: "+id);
        db.close();
    }
    public  void deleteMyDetail(String myName){
        SQLiteDatabase db = getReadableDatabase();
        db.execSQL("DELETE FROM " + TABLE_MYDETAIL + " WHERE " + COLUMN_NAME + "=\"" + myName + "\";");
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS"+TABLE_MYDETAIL);
        onCreate(db);
    }
    public String databaseToString(){
        String dbString="";
        SQLiteDatabase db =getWritableDatabase();
        String query="SELECT * FROM " + TABLE_MYDETAIL + " WHERE 1" ;
        Cursor c =db.rawQuery(query, null);
        c.moveToFirst();
        while(!c.isAfterLast()){
            if(c.getString(c.getColumnIndex("_marks"))!=null){
                dbString+= c.getString(c.getColumnIndex(COLUMN_ROLLNUMBER));
                dbString+=c.getString(c.getColumnIndex(COLUMN_NAME));
                dbString+=c.getString(c.getColumnIndex(COLUMN_MARKS));
                dbString += "\n";
            }
            c.moveToNext();
        }
        c.close();
        db.close();
        return dbString;
    }
    }

这是我的MainActivity

 package com.example.saranshagarwal.studentdetailsapp;


    public class MainActivity extends AppCompatActivity {
    EditText name,rollnumber,marks;
    MyDBHandler myDBHandler;
    TextView tv2;
    final Context context=this;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        name = (EditText) findViewById(R.id.editText2);
        rollnumber = (EditText) findViewById(R.id.editText5);
        marks = (EditText) findViewById(R.id.editText4);
        tv2=(TextView)findViewById(R.id.textView5);
        myDBHandler=new MyDBHandler(this,null,null,1);

    }
    public void addButtonClicked(View view){
        MyDetails myDetails=new MyDetails();
        myDetails.set_rollNumber(rollnumber.getText().toString());

        myDetails.set_name(marks.getText().toString());
        myDetails.set_marks(marks.getText().toString());
        myDBHandler.addMyDetail(myDetails);
        String dbString= myDBHandler.databaseToString();
        tv2.setText(dbString);
        name.setText("");
        rollnumber.setText("");
        marks.setText("");
    }
    public  void deleteButtonClicked(View view) {
        String inputText = name.getText().toString();
        myDBHandler.deleteMyDetail(inputText);

    }
     public void onViewClicked(View view){
      Dialog dialog= new Dialog(context);
      dialog.setContentView(R.layout.popup_on_view);
      TextView tv1=(TextView)findViewById(R.id.popup_text);
      String dbString= myDBHandler.databaseToString();
      tv1.setText(dbString);

          dialog.show();
    }
    }

Now when I click on the add Button the text is displayed of the name twice and marks once. What is the error?

afterEdit

Answer 1

您正在代码中添加标记代替名称

将您的代码更改为此

        myDetails.set_rollNumber(rollnumber.getText().toString());
        myDetails.set_name(name.getText().toString());
        myDetails.set_marks(marks.getText().toString());

可能原因是您访问数据库的方式。制作一个像这样的全局变量 -

private SQLiteDatabase db;

在您的构造函数MyDBHandler()中对此进行初始化

db=context.openOrCreateDatabase(DATABASE_NAME,DATABASE_VERSION,null);

然后在每个后续方法中使用它。

此外，您需要通过在MyDBHandler类中创建方法来显式关闭数据库。

public void close() throws SQLException {
        db.close();
    }

一旦完成db的工作，就调用它。从其他方法中删除db.close()语句。

此外，您需要在活动中为每个方法实现此功能

public void addButtonClicked(View view){

    MyDetails myDetails=new MyDetails();
    myDetails.set_rollNumber(rollnumber.getText().toString());

    myDetails.set_name(marks.getText().toString());
    myDetails.set_marks(marks.getText().toString());

    myDBHandler=new MyDBHandler(this,null,null,1);
    myDBHandler.addMyDetail(myDetails);

    String dbString= myDBHandler.databaseToString();
    myDBHandler.close();
    tv2.setText(dbString);
    name.setText("");
    rollnumber.setText("");
    marks.setText("");
}

希望这会有所帮助：）

数据库多次读取相同的数据

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