Firebase:更新一个整数值 [英] Firebase: update an integer value

问题描述

因此我正在对库存管理应用程序进行编码，因此我正在使用条形码扫描仪来扫描我的产品.我的想法是，每次扫描产品时，都需要在数据库中删除一小部分.像这样:扫描产品-> quantity = quantity-1

So im coding an inventory management app and I'm using a barcode scanner to scan my products. My idea is that every time that a product gets scanned I need to remove one quantity of it on my database. Like this: Scan product-->quantity=quantity-1

这是我的代码

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mFirestore = FirebaseFirestore.getInstance();
        scannerView = new ZXingScannerView(this);
        setContentView(scannerView);
       

    private void updateData() {

   //myresult is the item barcode
        final DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference("Items").child(myresult).child("itemquantity");
        mDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                long qty =(long) dataSnapshot.getValue();
                mDatabase.setValue(qty - 1);
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

    @Override
    public void onDestroy() {
        super.onDestroy();
        scannerView.stopCamera();
    }

   
    private void showMessageOKCancel(String message, DialogInterface.OnClickListener okListener) {
        new AlertDialog.Builder(addquantityactivity.this)
                .setMessage(message)
                .setPositiveButton("OK", okListener)
                .setNegativeButton("Cancel", null)
                .create()
                .show();
    }

    @Override
    public void handleResult(Result result) {
         myResult = result.getText();
        Log.d("QRCodeScanner", result.getText());
        Log.d("QRCodeScanner", result.getBarcodeFormat().toString());

        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("Scan Result");
        builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                updateData();
                scannerView.resumeCameraPreview(addquantityactivity.this);
                
            }
        });
        builder.setNeutralButton("Visit", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(myResult));
                startActivity(browserIntent);
            }
        });
        builder.setMessage(result.getText());
        AlertDialog alert1 = builder.create();
        alert1.show();

    }
}

我在我的 handleResult 函数中调用 updateData().我得到的错误是:

i call updateData() in my handleResult function. The error i get is :

java.lang.ClassCastException:无法将java.lang.String强制转换为java.lang.Long

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long

推荐答案

尝试一下:

long qty = dataSnapshot.getValue(Long.class);

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