firebase - Firestore 从集合字段中获取一个值然后返回（Kotlin）

Question

如何获取集合字段的值然后返回它？它可以currentUser用来获取uid等，但我需要获取另一个字段值。我在菜单上有一个按钮，并且仅当用户是 admin (usertype=1) on 时才显示onPrepareOptionsMenu。当我将具有函数的对象传递给oncreate. 但是onPrepareOptionsMenu之前加载oncreate所以我得到用户未初始化错误。我需要从“用户”集合中返回“用户类型”字段。

编辑：我发现从 firebase 获取数据是异步的，所以我需要其他方式。

获取用户详细信息

fun getUserDetails(activity: Activity) {

        // pass the collection name from which we wants the data.
        mFireStore.collection(Constants.USERS)
            // The document id to get the Fields of user.
            .document(getCurrentUserID())
            .get()
            .addOnSuccessListener { document ->
                // Here we have received the document snapshot which is converted into the User Data model object.
                val user = document.toObject(User::class.java)!!

                val sharedPreferences =
                    activity.getSharedPreferences(
                        Constants.MYSHOPPAL_PREFERENCES,
                        Context.MODE_PRIVATE
                    )

                // Create an instance of the editor which is help us to edit the SharedPreference.
                val editor: SharedPreferences.Editor = sharedPreferences.edit()
                editor.putString(
                    Constants.LOGGED_IN_USERNAME,
                    "${user.firstName} ${user.lastName}"
                )
                editor.apply()

                when (activity) {
                    is **ProductDetailActivity**-> {
                        // Call a function of base activity for transferring the result to it.
                        **activity.userDetailsSuccess(user)**
                    }
                }
            }
            .addOnFailureListener { e ->
                // Hide the progress dialog if there is any error. And print the error in log.
                when (activity) {
                    is ProductDetailsActivity -> {
                        activity.hideProgressDialog()
                    }
                }

                
            }
    }

产品详情活动

class ProductDetailsActivity : BaseActivity(), View.OnClickListener {

private lateinit var mProductDetails: Product
private lateinit var mUserDetails: User

// A global variable for product id.
private var mProductId: String = ""

/**
 * This function is auto created by Android when the Activity Class is created.
 */
override fun onCreate(savedInstanceState: Bundle?) {
    //This call the parent constructor
    super.onCreate(savedInstanceState)
    // This is used to align the xml view to this class
    setContentView(R.layout.activity_product_details)



    if (intent.hasExtra(Constants.EXTRA_PRODUCT_ID)) {
        mProductId =
            intent.getStringExtra(Constants.EXTRA_PRODUCT_ID)!!
    }

    var productOwnerId: String = ""

    if (intent.hasExtra(Constants.EXTRA_PRODUCT_OWNER_ID)) {
        productOwnerId =
            intent.getStringExtra(Constants.EXTRA_PRODUCT_OWNER_ID)!!
    }
    if (intent.hasExtra(Constants.EXTRA_PRODUCT_DETAILS)) {
        mProductDetails= intent.getParcelableExtra(Constants.EXTRA_PRODUCT_DETAILS)!!
    }

    setupActionBar()


    showProgressDialog(resources.getString(R.string.please_wait))

    // Call the function of FirestoreClass to get the userdetails.
    
    FirestoreClass().getUserDetails(this@ProductDetailsActivity)
}


override fun onPrepareOptionsMenu(menu: Menu?): Boolean {
    //admin can edit all products, seller can edit own products (i'm trying to get usertype BUT mUserDetails IS INITIALIZING AFTER onPrepareOptionsMenu
    var productOwnerId: String = ""
    if (intent.hasExtra(Constants.EXTRA_PRODUCT_OWNER_ID)) {
        productOwnerId =
            intent.getStringExtra(Constants.EXTRA_PRODUCT_OWNER_ID)!!
    }
    if (FirestoreClass().getCurrentUserID() != productOwnerId) {
    val menu1 = menu?.findItem(R.id.action_edit_product)
    if (menu1 != null) { //null check
        menu1.setVisible(false) //menuyu gizle
    }
    }
    return true


}

override fun onCreateOptionsMenu(menu: Menu?): Boolean {
    menuInflater.inflate(R.menu.product_details_menu, menu)
    return true
}

ProductDetailsActivity 上的函数

   fun userDetailsSuccess(user: User) {
        mUserDetails = user
    }

示例：getCurrentUserID 用于返回 currentUserID（我想从“users”集合返回“usertype”字段）

fun getCurrentUserID(): String {
    // An Instance of currentUser using FirebaseAuth
    val currentUser = FirebaseAuth.getInstance().currentUser

    // A variable to assign the currentUserId if it is not null or else it will be blank.
    var currentUserID = ""
    if (currentUser != null) {
        currentUserID = currentUser.uid
    }

    return currentUserID
}

标签： firebasekotlingoogle-cloud-firestore