NewPostActivity.kt

package com.google.firebase.quickstart.database.kotlin

import android.os.Bundle
import android.text.TextUtils
import android.util.Log
import android.widget.Toast
import com.google.firebase.database.DataSnapshot
import com.google.firebase.database.DatabaseError
import com.google.firebase.database.DatabaseReference
import com.google.firebase.database.FirebaseDatabase
import com.google.firebase.database.ValueEventListener
import com.google.firebase.quickstart.database.R
import com.google.firebase.quickstart.database.kotlin.models.Post
import com.google.firebase.quickstart.database.kotlin.models.User
import kotlinx.android.synthetic.main.activity_new_post.fabSubmitPost
import kotlinx.android.synthetic.main.activity_new_post.fieldBody
import kotlinx.android.synthetic.main.activity_new_post.fieldTitle
import java.util.HashMap

class NewPostActivity : BaseActivity() {

    // [START declare_database_ref]
    private lateinit var database: DatabaseReference
    // [END declare_database_ref]

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_new_post)

        // [START initialize_database_ref]
        database = FirebaseDatabase.getInstance().reference
        // [END initialize_database_ref]

        fabSubmitPost.setOnClickListener { submitPost() }
    }

    private fun submitPost() {
        val title = fieldTitle.text.toString()
        val body = fieldBody.text.toString()

        // Title is required
        if (TextUtils.isEmpty(title)) {
            fieldTitle.error = REQUIRED
            return
        }

        // Body is required
        if (TextUtils.isEmpty(body)) {
            fieldBody.error = REQUIRED
            return
        }

        // Disable button so there are no multi-posts
        setEditingEnabled(false)
        Toast.makeText(this, "Posting...", Toast.LENGTH_SHORT).show()

        // [START single_value_read]
        val userId = uid
        database.child("users").child(userId).addListenerForSingleValueEvent(
                object : ValueEventListener {
                    override fun onDataChange(dataSnapshot: DataSnapshot) {
                        // Get user value
                        val user = dataSnapshot.getValue(User::class.java)

                        // [START_EXCLUDE]
                        if (user == null) {
                            // User is null, error out
                            Log.e(TAG, "User $userId is unexpectedly null")
                            Toast.makeText(baseContext,
                                    "Error: could not fetch user.",
                                    Toast.LENGTH_SHORT).show()
                        } else {
                            // Write new post
                            writeNewPost(userId, user.username.toString(), title, body)
                        }

                        // Finish this Activity, back to the stream
                        setEditingEnabled(true)
                        finish()
                        // [END_EXCLUDE]
                    }

                    override fun onCancelled(databaseError: DatabaseError) {
                        Log.w(TAG, "getUser:onCancelled", databaseError.toException())
                        // [START_EXCLUDE]
                        setEditingEnabled(true)
                        // [END_EXCLUDE]
                    }
                })
        // [END single_value_read]
    }

    private fun setEditingEnabled(enabled: Boolean) {
        fieldTitle.isEnabled = enabled
        fieldBody.isEnabled = enabled
        if (enabled) {
            fabSubmitPost.show()
        } else {
            fabSubmitPost.hide()
        }
    }

    // [START write_fan_out]
    private fun writeNewPost(userId: String, username: String, title: String, body: String) {
        // Create new post at /user-posts/$userid/$postid and at
        // /posts/$postid simultaneously
        val key = database.child("posts").push().key
        if (key == null) {
            Log.w(TAG, "Couldn't get push key for posts")
            return
        }

        val post = Post(userId, username, title, body)
        val postValues = post.toMap()

        val childUpdates = HashMap<String, Any>()
        childUpdates["/posts/$key"] = postValues
        childUpdates["/user-posts/$userId/$key"] = postValues

        database.updateChildren(childUpdates)
    }
    // [END write_fan_out]

    companion object {

        private const val TAG = "NewPostActivity"
        private const val REQUIRED = "Required"
    }
}