java - 从检索到的 firebase json 对象中提取单个数据值

Question

在我的 android 应用程序中，我只想从 firebase json 对象的所有节点中检索单个值并检查...我的 firebase 数据库看起来像 ->

现在我正在使用此代码来完成我的任务，但我每次都得到 null 作为输出..

public class optChos extends AppCompatActivity {
DatabaseReference ref;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_opt_chos);

    final FirebaseDatabase database = FirebaseDatabase.getInstance();
    ref = database.getReference("vendorDtl");
}

public void fetchkey(View view) {
    EditText etx=findViewById(R.id.etkey);
    String keysrch=etx.getText().toString();
    Log.i("optionchoose","fetchkeycalled");
    Toast.makeText(getApplicationContext(),"Key finfing",Toast.LENGTH_SHORT).show();


    ref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot vst:dataSnapshot.getChildren()) {
                vendor vn = vst.getValue(vendor.class);
                Toast.makeText(getApplicationContext(), "Email is-> " + vn.getNam(), Toast.LENGTH_SHORT).show();
                Toast.makeText(getApplicationContext(), "key is-> " + vn.getVky(), Toast.LENGTH_SHORT).show();
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Toast.makeText(getApplicationContext(),"nothing fetched",Toast.LENGTH_SHORT).show();
        }
    });
}



@Override
protected void onStart() {
    super.onStart();
    ref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot vst:dataSnapshot.getChildren()) {
                vendor vn = vst.getValue(vendor.class);
                Toast.makeText(getApplicationContext(), "Email is-> " + vn.getNam(), Toast.LENGTH_SHORT).show();
                Toast.makeText(getApplicationContext(), "key is-> " + vn.getVky(), Toast.LENGTH_SHORT).show();
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Toast.makeText(getApplicationContext(),"nothing fetched",Toast.LENGTH_SHORT).show();
        }
    });
}

}

这里fetchkey(View view)是按钮的onclick函数..

I want to retrieve that vid from every node and check with a user entered value ..How can i do that?

Answer 1

要从每个节点获取 vid 字段的值，请使用以下代码:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference vendorDtlRef = rootRef.child("vendorDtl");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String vid = ds.child("vid").getValue(String.class);
            Log.d("TAG", vid);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
vendorDtlRef.addListenerForSingleValueEvent(eventListener);