所以现在我正在尝试做一个理财应用程序。我想让余额在用户增加收入或支出时自动增加或减少。我正在使用sqlite作为数据库。有人能帮我解释一下怎么做吗？我不知道怎么做。

public class MoneyDBHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "MONEYPROJECT.DB";
    private static final int DATABASE_VERSION = 6;
    private static final String TABLE_NAME = "MAINTABLE";
    private static final String UID = "_id";
    private static final String EXPENSE = "expenses";
    private static final String INCOME = "incomes";
    private static final String DESC = "description";
    private static final String DATE= "date";
    private static final String BALANCE= "balance";
    private static final String createquery = "CREATE TABLE "+TABLE_NAME+" ("+UID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+BALANCE+" INT(9) ,"+EXPENSE+" INT(9),"+INCOME+" INT(9), "+DATE+" TEXT(8), "+DESC+" VARCHAR(100) );";
    private static final String DROP_TABLE="DROP TABLE IF EXISTS "+ TABLE_NAME;

    public MoneyDBHelper(@Nullable Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(createquery);
    }

    public long insertDataincome(String income, String date){
        SQLiteDatabase db= this.getWritableDatabase();
        ContentValues contentValues=new ContentValues();
        contentValues.put(MoneyDBHelper.INCOME, income);
        contentValues.put(MoneyDBHelper.DATE, date);
        long id= db.insert(MoneyDBHelper.TABLE_NAME,null, contentValues);
        return id;
    }

    public long insertDataexpense(String expense, String date, String desc){
        SQLiteDatabase db= this.getWritableDatabase();
        ContentValues contentValues=new ContentValues();
        contentValues.put(MoneyDBHelper.EXPENSE, expense);
        contentValues.put(MoneyDBHelper.DESC, desc);
        contentValues.put(MoneyDBHelper.DATE, date);
        long id= db.insert(MoneyDBHelper.TABLE_NAME,null, contentValues);
        return id;
    }

以上是我的数据库设计...我想平衡的价值增加或减少每当用户输入收入或支出...我试图使目前的平衡在这里。

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";
    private EditText mDisplayDate;
    private DatePickerDialog.OnDateSetListener mDateSetListener;

    Button calendarbt;
    Button helpbt;
    private Object view;
    Context context;
    MoneyDBHelper moneyDBHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final TextView balance = (TextView) findViewById(R.id.balance);
        final EditText expensebox = (EditText) findViewById(R.id.expenseamount);
        final EditText expensedesc = (EditText) findViewById(R.id.expensedesc);
        final Button addminus = (Button) findViewById(R.id.add2);
        final EditText incomebox = (EditText) findViewById(R.id.incomeamount);
        final Button addplus = (Button) findViewById(R.id.add1);
        final EditText expensedate = (EditText) findViewById(R.id.expensedate);

        moneyDBHelper= new MoneyDBHelper(this);
        final SQLiteDatabase[] sqLiteDatabase = {moneyDBHelper.getWritableDatabase()};

        mDisplayDate = (EditText) findViewById(R.id.expensedate);
        mDisplayDate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Calendar cal = Calendar.getInstance();
                int year = cal.get(Calendar.YEAR);
                int month = cal.get(Calendar.MONTH);
                int day = cal.get(Calendar.DAY_OF_MONTH);

                DatePickerDialog dialog = new DatePickerDialog(
                        MainActivity.this,
                        android.R.style.Theme_Black,
                        mDateSetListener,
                        year,month,day);
                dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
                dialog.show();
            }
        });

        mDateSetListener = new DatePickerDialog.OnDateSetListener() {
            @Override
            public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
                month = month + 1;
                Log.d(TAG, "onDateSet: dd/mm/yyyy: "+  month + "/" + dayOfMonth + "/" + year);
                String date = month + "/" + dayOfMonth + "/" + year;
                mDisplayDate.setText(date);
            }
        };

        Button plusbt = (Button) findViewById(R.id.plus);
        plusbt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                incomebox.setVisibility(View.VISIBLE);
                addplus.setVisibility(View.VISIBLE);
                expensebox.setVisibility(View.GONE);
                addminus.setVisibility(View.GONE);
                expensedesc.setVisibility(View.GONE);
                expensedate.setVisibility(View.VISIBLE);
            }
        });

        Button minusbt= (Button) findViewById(R.id.minus);
        minusbt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                expensebox.setVisibility(View.VISIBLE);
                addminus.setVisibility(View.VISIBLE);
                expensedesc.setVisibility(View.VISIBLE);
                incomebox.setVisibility(View.GONE);
                addplus.setVisibility(View.GONE);
                expensedate.setVisibility(View.VISIBLE);
            }
        });
        addplus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(incomebox.length()==0){
                    incomebox.setError("Please Enter Income");
                    Toast.makeText(MainActivity.this, "Please fill all field", Toast.LENGTH_LONG).show();
                }
                else if (expensedate.length()==0){
                    expensedate.setError("Please Enter Date");
                    Toast.makeText(MainActivity.this, "Please fill all field", Toast.LENGTH_LONG).show();
                }
                else{
                    Toast.makeText(MainActivity.this, "Sucessful", Toast.LENGTH_LONG).show();
                    String income=incomebox.getText().toString();
                    String date=expensedate.getText().toString();

                    long id= moneyDBHelper.insertDataincome(income,date);
                }
            };
        });

        addminus.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(expensebox.length()==0){
                    expensebox.setError("Please Enter Expense");
                    Toast.makeText(MainActivity.this, "Please fill all field", Toast.LENGTH_LONG).show();
                }
                else if (expensedate.length()==0){
                    expensedate.setError("Please Enter Date");
                    Toast.makeText(MainActivity.this, "Please fill all field", Toast.LENGTH_LONG).show();
                }
                else if (expensedesc.length()==0){
                    expensedesc.setError("Please Enter Date");
                    Toast.makeText(MainActivity.this, "Please fill all field", Toast.LENGTH_LONG).show();
                }
                else{
                    Toast.makeText(MainActivity.this, "Sucessful", Toast.LENGTH_LONG).show();
                    String expense=expensebox.getText().toString();
                    String date=expensedate.getText().toString();
                    String desc=expensedesc.getText().toString();

                    long id= moneyDBHelper.insertDataexpense(expense,date,desc);
                }
            };
        });