Java 如何作为方法的结果返回DocumentSnapShot？

获取（DocumentSnapShot DocumentSnapShot）参数的自定义对象。也是Firebase中的一个内部对象，用于检索快照并将值设置为“我的自定义模型”也有其参数（DocumentSnapShot DocumentSnapShot）。但是，我希望从Firebase获取数据，并将其传递给我的自定义参数，因为我的参数需要多个数据，而不仅仅是Firebase。如果没有覆盖，就不可能迭代Firestore

代码如下：

public UserSettings getUserSettings(DocumentSnapshot documentSnapshot){
    Log.d(TAG, "getUserSettings: retrieving user account settings from firestore");

    DocumentReference mSettings = mFirebaseFirestore.collection("user_account_settings").document(userID);
    mSettings.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
        @Override
        public void onSuccess(DocumentSnapshot documentSnapshot) {
            UserAccountSettings settings = documentSnapshot.toObject(UserAccountSettings.class);
            settings.setDisplay_name(documentSnapshot.getString("display_name"));
            settings.setUsername(documentSnapshot.getString("username"));
            settings.setWebsite(documentSnapshot.getString("website"));
            settings.setProfile_photo(documentSnapshot.getString("profile_photo"));
            settings.setPosts(documentSnapshot.getLong("posts"));
            settings.setFollowers(documentSnapshot.getLong("followers"));
            settings.setFollowing(documentSnapshot.getLong("following"));
        }
    });
}

公共用户设置getUserSettings（DocumentSnapshot DocumentSnapshot）{ d（标记“getUserSettings:从firestore检索用户帐户设置”）； DocumentReference mSettings=mFirebaseFirestore.collection（“用户帐户设置”）.document（用户ID）； mSettings.get（）.addOnSuccessListener（新OnSuccessListener（））{ @凌驾 成功时公共无效（文档快照文档快照）{ UserAccountSettings设置=documentSnapshot.toObject（UserAccountSettings.class）； settings.setDisplay_name（documentSnapshot.getString（“display_name”））； settings.setUsername（documentSnapshot.getString（“用户名”）； settings.setWebsite（documentSnapshot.getString（“网站”）； settings.setProfile_photo（documentSnapshot.getString（“profile_photo”）； settings.setPosts（documentSnapshot.getLong（“posts”）； setFollowers（documentSnapshot.getLong（“followers”）； settings.setFollowing（documentSnapshot.getLong（“following”）； } }); }

---

您现在无法返回尚未加载的内容。Firestore异步加载数据

，因为这可能需要一些时间。根据您的连接速度和状态，数据可用可能需要几百毫秒到几秒钟的时间。如果要将
settings
对象传递给另一个方法，只需在
onSuccess（）方法中调用该方法并将该对象作为参数传递即可。因此，一个快速解决方案是：

@Override
public void onSuccess(DocumentSnapshot documentSnapshot) {
    UserAccountSettings settings = documentSnapshot.toObject(UserAccountSettings.class);
    yourMethod(settings);
}

还有一件事要提的是，您不需要将这些值设置为已经具有它们的对象。您已经将数据作为对象从数据库中获取

所以请记住，
onSuccess（）
方法具有异步行为，这意味着即使在从数据库获取数据之前，也会调用该方法。如果要在该方法之外使用
设置
对象，则需要创建自己的
回调
。要实现这一点，首先需要创建如下界面：

public interface MyCallback {
    void onCallback(UserAccountSettings settings);
}

public void readData(MyCallback myCallback) {
    DocumentReference mSettings = mFirebaseFirestore.collection("user_account_settings").document(userID);
    mSettings.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
        @Override
        public void onSuccess(DocumentSnapshot documentSnapshot) {
            UserAccountSettings settings = documentSnapshot.toObject(UserAccountSettings.class);
            myCallback.onCallback(settings);

        }
    });
}

readData(new MyCallback() {
    @Override
    public void onCallback(UserAccountSettings settings) {
        Log.d("TAG", settings.getDisplay_name());
    }
});

然后，您需要创建一个从数据库中实际获取数据的方法。此方法应如下所示：

public interface MyCallback {
    void onCallback(UserAccountSettings settings);
}

public void readData(MyCallback myCallback) {
    DocumentReference mSettings = mFirebaseFirestore.collection("user_account_settings").document(userID);
    mSettings.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
        @Override
        public void onSuccess(DocumentSnapshot documentSnapshot) {
            UserAccountSettings settings = documentSnapshot.toObject(UserAccountSettings.class);
            myCallback.onCallback(settings);

        }
    });
}

readData(new MyCallback() {
    @Override
    public void onCallback(UserAccountSettings settings) {
        Log.d("TAG", settings.getDisplay_name());
    }
});

这是在
onSuccess（）方法之外使用
UserAccountSettings
类的对象的唯一方法。有关更多信息，您还可以查看此
使用
LiveData
作为返回类型，并观察其值的变化以执行所需的操作

private MutableLiveData<UserAccountSettings> userSettingsMutableLiveData = new MutableLiveData<>();

public MutableLiveData<UserAccountSettings> getUserSettings(DocumentSnapshot documentSnapshot){

    DocumentReference mSettings = mFirebaseFirestore.collection("user_account_settings").document(userID);
    mSettings.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
        @Override
        public void onSuccess(DocumentSnapshot documentSnapshot) {
            UserAccountSettings settings = documentSnapshot.toObject(UserAccountSettings.class);
            settings.setDisplay_name(documentSnapshot.getString("display_name"));
            settings.setUsername(documentSnapshot.getString("username"));
            settings.setWebsite(documentSnapshot.getString("website"));
            settings.setProfile_photo(documentSnapshot.getString("profile_photo"));
            settings.setPosts(documentSnapshot.getLong("posts"));
            settings.setFollowers(documentSnapshot.getLong("followers"));
            settings.setFollowing(documentSnapshot.getLong("following"));

            userSettingsMutableLiveData.setValue(settings);
        }
    });

    return userSettingsMutableLiveData;
}

getUserSettings().observe(this, new Observer<UserAccountSettings>() {
    @Override
    public void onChanged(UserAccountSettings userAccountSettings) {
        //here, do whatever you want on `userAccountSettings`
    }
});