Question

如果我有一个Firebase Firestore数据库，我已经为与右边的集合对应的文档检索了DocumentSnapshot并存储在document变量中，那么我该如何检索该值DocumentSnapshot在该字段＆＃34;用户名＆＃34;？该字段具有字符串值。

Answer 1

DocumentSnapshot有一个方法getString()，它取一个字段的名称并将其值作为字符串返回。

String value = document.getString("username");

Answer 2

您需要执行DocumentReference才能获取文档中的内容。

一个简单的就是这样。

DocumentReference docRef = myDB.collection("users").document("username");
docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
@Override
     public void onComplete(@NonNull Task<DocumentSnapshot> task) {
          if (task.isSuccessful()) {
               DocumentSnapshot document = task.getResult();
                    if (document != null) {
                         Log.i("LOGGER","First "+document.getString("first"));
                         Log.i("LOGGER","Last "+document.getString("last"));
                         Log.i("LOGGER","Born "+document.getString("born"));
                    } else {
                         Log.d("LOGGER", "No such document");
                    }
               } else {
                    Log.d("LOGGER", "get failed with ", task.getException());
                }
          }
     });

缺点是您需要知道您的文档ID才能获得字段值。

Answer 3

您可以使用get方法获取字段值

String username = (String) docuemnt.get("username");  //if the field is String
Boolean b = (Boolean) document.get("isPublic");       //if the field is Boolean
Integer i = (Integer) document.get("age")             //if the field is Integer

结帐DocumentSnapshot

的文档

Answer 4

当我在onComplete内部时，我只能以Strings形式引用该字段的数据，但是当我尝试在它外部时引用它时。我收到一个nullPointerException，它使我的活动崩溃。

// Gets user document from Firestore as reference
    DocumentReference docRef = mFirestore.collection("users").document(userID);

    docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
        @Override
        public void onComplete(@NonNull Task<DocumentSnapshot> task) {
            if (task.isSuccessful()) {
                DocumentSnapshot document = task.getResult();
                if (document.exists()) {

                    Log.d(TAG, "DocumentSnapshot data: " + document.getData());
                    Log.d(TAG, "db firstName getString() is: " + document.getString("firstName"));
                    Log.d(TAG, "db lastName getString() is: " + document.getString("lastName"));

                    mFirstName = (String) document.getString("firstName");
                    mLastName = (String) document.getString("lastName");
                    Log.d(TAG, "String mFirstName is: " + mFirstName);
                    Log.d(TAG, "String mLastName is: " + mLastName);

                } else {
                    Log.d(TAG, "No such document");
                }
            } else {
                Log.d(TAG, "get failed with ", task.getException());
            }
        }
    });

    //string checking outside the docRef.get().addOnCompleteListener code
    //commented it out because it causes a java.lang.NullPointerException: println needs a message
    //Log.v("NAME", mFirstName);
    //Log.v("NAME", mLastName);

    // sets the text on the TextViews
    tvFirstName = (TextView)findViewById(R.id.tvFirstName);
    tvFirstName.setText(mFirstName);
    tvLastName = (TextView)findViewById(R.id.tvLastName);
    tvLastName.setText(mLastName);

Answer 5

这里是获取文档价值的另一种简单方法（针对您的情况）：

Firestore.instance
.collection('users').document('xsajAansjdna')
.get()
.then((value) =>
print("Fetched ==>>>"+value.data["username"]));

Firestore获取DocumentSnapshot的字段值

5 个答案: