当应用程序可以访问互联网时，如何离线存储数据然后在 Firebase 中上传？

Question

我正在创建一个应用程序，它接受用户的输入并上传到 Firebase。如果该应用程序可以访问互联网，则该应用程序可以正常工作。但是如果应用无法访问互联网，我想让我的应用接受输入并离线存储这些数据，然后在应用可以访问互联网时上传到 Firebase。

我也使用“磁盘持久性”

FirebaseDatabase.getInstance().setPersistenceEnabled(true);

还有“保持数据新鲜”

DatabaseReference scoresRef = FirebaseDatabase.getInstance().getReference("scores");
scoresRef.keepSynced(true);

但这对我不起作用。也许我没有正确使用它。

我的代码是

AddDataActivity

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    binding = ActivityAddDataBinding.inflate(getLayoutInflater());
    setContentView(binding.getRoot());
    Objects.requireNonNull(getSupportActionBar()).setDisplayHomeAsUpEnabled(true);
    getSupportActionBar().setTitle("Add Data");
    FirebaseDatabase database = FirebaseDatabase.getInstance();
    database.getReference().child("Users").child(FirebaseAuth.getInstance().getUid()).child("data_added_by_user").keepSynced(true);
    progressDialog = new ProgressDialog(AddDataActivity.this);
    progressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
    progressDialog.setTitle("Adding Data");
    progressDialog.setMessage("Please Wait ...");
    progressDialog.setCancelable(false);
    progressDialog.setCanceledOnTouchOutside(false);

    Intent mintent = getIntent();
    String activity = mintent.getStringExtra("activity");
    if (activity.equals("list")){
        String date = mintent.getStringExtra("date");
        String name = mintent.getStringExtra("name");
        String weight = mintent.getStringExtra("weight");
        String rate = mintent.getStringExtra("rate");
        binding.editDate.setText(date);
        binding.editName.setText(name);
        binding.editWeight.setText(weight);
        binding.editRate.setText(rate);
    }





    binding.btnSubmit.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (binding.editDate.getText().toString().length() == 0) {
                Toast.makeText(AddDataActivity.this, "Enter Date", Toast.LENGTH_SHORT).show();
            } else if (binding.editName.getText().toString().length() == 0) {
                Toast.makeText(AddDataActivity.this, "Enter Name", Toast.LENGTH_SHORT).show();

            } else if (binding.editWeight.getText().toString().length() == 0) {
                Toast.makeText(AddDataActivity.this, "Enter Weight", Toast.LENGTH_SHORT).show();

            } else {
                if (notValidDateFormat(binding.editDate.getText().toString(), "yyyy-MM-dd")
                        || notValidDateFormat(binding.editDate.getText().toString(), "yyyy/MM/dd")
                        || notValidDateFormat(binding.editDate.getText().toString(), "yyyy.MM.dd")){

                    progressDialog.show();
                    DataModel data = new DataModel();
                    int weight = Integer.parseInt(binding.editWeight.getText().toString());
                    int rate = Integer.parseInt(binding.editRate.getText().toString());
                    data.setDate(binding.editDate.getText().toString());
                    data.setName(binding.editName.getText().toString());
                    data.setWeight(weight);
                    data.setRate(rate);
                    data.setAddedBy(FirebaseAuth.getInstance().getUid());
                    if (!activity.equals("list")) {
                        data.setAddedTime(new Date().getTime());
                        data.setSell(true);
                        String dataId = database.getReference().child("Users").child(FirebaseAuth.getInstance().getUid()).child("data_added_by_user").push().getKey();
                        data.setDataId(dataId);
                        database.getReference().child("Users").child(FirebaseAuth.getInstance().getUid()).child("data_added_by_user").child(dataId).setValue(data)
                                .addOnSuccessListener(new OnSuccessListener<Void>() {
                                    @Override
                                    public void onSuccess(Void unused) {
                                        progressDialog.dismiss();
                                        Toast.makeText(AddDataActivity.this, "Data Added!", Toast.LENGTH_SHORT).show();
                                        Intent intent = new Intent(AddDataActivity.this, ItemListActivity.class);
                                        startActivity(intent);
                                        finish();
                                    }
                                });
                    } else{
                        database.getReference().child("Users").child(FirebaseAuth.getInstance().getUid()).child("data_added_by_user").child(mintent.getStringExtra("id")).child("modifiedTime").setValue(new Date().getTime());
                        database.getReference().child("Users").child(FirebaseAuth.getInstance().getUid()).child("data_added_by_user").child(mintent.getStringExtra("id")).child("date").setValue(binding.editDate.getText().toString());
                        database.getReference().child("Users").child(FirebaseAuth.getInstance().getUid()).child("data_added_by_user").child(mintent.getStringExtra("id")).child("name").setValue(binding.editName.getText().toString());
                        database.getReference().child("Users").child(FirebaseAuth.getInstance().getUid()).child("data_added_by_user").child(mintent.getStringExtra("id")).child("weight").setValue(weight);
                        database.getReference().child("Users").child(FirebaseAuth.getInstance().getUid()).child("data_added_by_user").child(mintent.getStringExtra("id")).child("rate").setValue(rate)
                                .addOnSuccessListener(new OnSuccessListener<Void>() {
                                    @Override
                                    public void onSuccess(Void unused) {
                                        progressDialog.dismiss();
                                        Toast.makeText(AddDataActivity.this, "Data Modified!", Toast.LENGTH_SHORT).show();
                                        Intent intent = new Intent(AddDataActivity.this, ItemListActivity.class);
                                        startActivity(intent);
                                        finish();
                                    }
                                });
                    }

                } else {
                    Toast.makeText(AddDataActivity.this, "Invalid Date Format! ", 
       Toast.LENGTH_SHORT).show();
                }
            }
        }

    });


}

对于磁盘持久性，我创建了与项目名称相同的新java类

public class PhoNote extends Application {

@Override
public void onCreate() {
    super.onCreate();
    FirebaseDatabase.getInstance().setPersistenceEnabled(true);
  }
}

谢谢！！

Answer 1

在写入数据库时​​，Firebase 不会将缺少互联网连接视为错误情况。相反，它会在这种情况下将数据保存在内存中（如果您enabled disk persistence，也将数据保存在磁盘上）并在重新建立连接时将其同步到服务器。

当您将完成侦听器或成功侦听器附加到写入操作时，只有在服务器上提交或拒绝操作时才会触发。在某些情况下这可能很重要，但在大多数情况下您实际上并不需要

这意味着在大多数情况下，在对 Firebase 进行写入操作时，您不需要完成侦听器，甚至不需要进度对话框。相反，您应该将它们视为本地的、即时的并且在 setValue() 调用执行时完成。

所以：

database.getReference().child("Users").child(FirebaseAuth.getInstance().getUid()).child("data_added_by_user").child(dataId).setValue(data);

Toast.makeText(AddDataActivity.this, "Data Added!", Toast.LENGTH_SHORT).show();
Intent intent = new Intent(AddDataActivity.this, ItemListActivity.class);
startActivity(intent);
finish();