如何让号码保持最新号码而不是回到默认号码？

我的 TxnNo(A0010001) 来自 Unitcode(A001) + LastTxnNo(0001)。这是我的按钮点击。

Db_Save.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Model txn = new Model();// initialize your model class first
                BigDecimal paidAmt = new BigDecimal(D_Amount.getText().toString()).setScale(2, RoundingMode.HALF_UP);
                txn.setName(D_Name.getText().toString());
                txn.setTxnNo(D_Txn.getText().toString());
                txn.setTxnDate(Select_Date.getText().toString());
                txn.setAmount(paidAmt);
                txn.setDescription1(D_Description.getSelectedItem().toString());
                txn.setDescription2(Ds_Description.getText().toString());

                try {

                    SQLiteDatabase db = mSQLiteHelper.getWritableDatabase();
                    ContentValues cv = new ContentValues();
                    cv.put("name", txn.getName());
                    cv.put("TxnNo", txn.getTxnNo());
                    cv.put("TxnDate", txn.getTxnDate());
                    cv.put("Amount", txn.getAmount().toPlainString());
                    cv.put("Description1", txn.getDescription1());
                    cv.put("Description2", txn.getDescription2());
                    db.insert("Donation_Details", null, cv);
                    db.close();
                    increaseNumber++;
                    populate_TxnNo();
                    Toast.makeText(Donation_Page.this, "Add successfully", Toast.LENGTH_SHORT).show();
                } catch (Exception e) {
                    e.printStackTrace();
                }



            }
        });

I put increaseNumber++;以确保它会自动增加。所以每次我点击按钮。号码将从“A0010001”更改为“A0010002”，依此类推。但是一旦我离开这个页面，然后再次进入。它将返回“A0010001”。如何让它保持最新的数字而不是回到“A0010001”。这是设置编号的方法。

 private void populate_TxnNo() {

        int lastNumber = Integer.valueOf(txn.getLastTxnNo());
        lastNumber = lastNumber + increaseNumber;
        String stringLast = String.format("%04d", lastNumber);
        String txnNo = txn.getUnit_Code() + stringLast;
        //increaseNumber++;
        D_Txn.setText(txnNo);
    }

UPDATE

所以对于我来说要理解共同偏好我将这些代码放入新按钮中。

Db_New.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                increaseNumber++;
                populate_TxnNo();

            }
        });

但我不知道如何使用共同偏好即使我看到代码示例...任何人都可以为我解释一下吗？如何使用该代码？

SharedPreferences prefs;
    SharedPreferences.Editor edit;
prefs=this.getSharedPreferences("yourPrefsKey",Context.MODE_PRIVATE);

        edit=prefs.edit();  
edit.putString("yourKey", txnNo);
            edit.commit();  

String txnNo = prefs.getString("yourKey", null);

首先声明这两个变量

SharedPreferences sharedPreferences;
SharedPreferences.Editor editor;
int count;

接下来将这些添加到onCreate method

sharedPreferences = getApplicationContext().getSharedPreferences("counters", MODE_PRIVATE);
editor = sharedPreferences.edit();
count = sharedPreferences.getInt("counter", 0);

最后修改populate_TxnNo方法

  private void populate_TxnNo() {

        int a = count++;
        int lastNumber = Integer.valueOf(txn.getLastTxnNo());
        lastNumber = lastNumber + a;
        String stringLast = String.format("%04d", lastNumber);
        String txnNo = txn.getUnit_Code() + stringLast;
        D_Txn.setText(txnNo);
        editor.putInt("counter", ++a);
        editor.commit();
    }