android - Android Kotlin:如何从Firebase删除数据

Question

我是Android Kotlin的新手。单击应用上的按钮时，我尝试从Cloud Firebase删除数据。我在适配器上做了一些必要的代码，但是如何在Activity上调用数据库集合？ ı在下面分享了我的适配器和我的 Activity 代码。

class NoteAdapter(val titleText: ArrayList<String>, val rowImage: ArrayList<String>, val noteText: ArrayList<String>, val listener: onClick) : RecyclerView.Adapter<NoteAdapter.NoteHolder>() {


    interface onClick {

        fun onItemClickListener(v: View, pos: Int, data: Any)


    }


    class NoteHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

        val itemImage : ImageView = itemView.findViewById(R.id.recyclerImage)
        val itemDelete: ImageView = itemView.findViewById(R.id.delete)


    }


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): NoteHolder {

        val v = LayoutInflater.from(parent.context).inflate(R.layout.recycler_row, parent, false)
        return NoteHolder(v)
    }

    override fun onBindViewHolder(holder: NoteHolder, position: Int) {

        holder.itemView.recyclerTitleText.text = titleText[position]
        Picasso.get().load(rowImage[position]).resize(150,150).into(holder.itemImage)

        holder.itemView.setOnClickListener {


            val intent = Intent(holder.itemView.context, PastNotesActivity:: class.java)
            intent.putExtra("oldTitle", titleText[position])
            intent.putExtra("oldNote", noteText[position])
            intent.putExtra("oldImage", rowImage[position])
            holder.itemView.context.startActivity(intent)


        }

        holder.itemDelete.setOnClickListener { v: View ->

            titleText.removeAt(position)
            noteText.removeAt(position)
            rowImage.removeAt(position)

            notifyItemRemoved(position)

            listener.onItemClickListener(v, position, holder.itemView)
        }

    }

    override fun getItemCount(): Int {

        return titleText.size
    }


    override fun getItemId(position: Int):Long  {
        return position.toLong()
    }

    override fun getItemViewType(position: Int):Int {
        return position
    }


}

这是我的 Activity 代码，我在此 Activity 中创建itemDelete乐趣，但是如何在此乐趣中定义适配器代码？并且我尝试在文档中写“{id.data}”，但没有用，我应该写什么？

class ListViewActivity : AppCompatActivity() {

    var selectedPicture: Uri? = null

    private  lateinit var auth: FirebaseAuth
    private lateinit var db : FirebaseFirestore

    var titleTextFromFB : ArrayList<String> = ArrayList()
    var noteTextFromFB : ArrayList<String> = ArrayList()
    var imageFromFB : ArrayList<String> = ArrayList()


    var adapter: NoteAdapter? = null



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

        auth = FirebaseAuth.getInstance()
        db = FirebaseFirestore.getInstance()

        getDataFromFirestore()

        // recyclerview

        var layoutManager = LinearLayoutManager(this)
        recyclerView.layoutManager = layoutManager

       // adapter = NoteAdapter(titleTextFromFB, imageFromFB, noteTextFromFB)
        //recyclerView.adapter = adapter

        adapter = NoteAdapter(titleTextFromFB, imageFromFB, noteTextFromFB, object: NoteAdapter.onClick{

            override fun onItemClickListener(v: View, pos: Int, data: Any) {

                when(v.id){

                    R.id.delete -> itemDelete(data)

                }

            }

        })

        recyclerView.adapter = adapter

    }


    override fun onCreateOptionsMenu(menu: Menu?): Boolean {

        val menuInflater = menuInflater
        menuInflater.inflate(R.menu.add_note, menu)

        return super.onCreateOptionsMenu(menu)
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {

        if (item.itemId == R.id.add_note_click) {
            // Take Notes Activity
            val intent = Intent(applicationContext, TakeNotesActivity::class.java)
            intent.putExtra("info","new")
            startActivity(intent)

        } else if (item.itemId == R.id.log_out) {

            val alert = AlertDialog.Builder(this)

            alert.setTitle("Log Out")
            alert.setMessage("Are you sure to logout from the app ?")
            alert.setPositiveButton("Yes") {dialog, which ->

                auth.signOut()
                val intent = Intent(applicationContext, MainActivity::class.java)
                startActivity(intent)
                finish()
            }

            alert.setNegativeButton("No") {dialog, which ->

            }

            alert.show()

        }

        return super.onOptionsItemSelected(item)
    }

    // get data from firestore

    fun getDataFromFirestore() {

        db.collection("Notes").orderBy("date", Query.Direction.DESCENDING).addSnapshotListener{ snapshot, exception ->

            if (exception != null) {

                // If there is a error ,

                Toast.makeText(applicationContext, exception.localizedMessage.toString(), Toast.LENGTH_LONG).show()

            } else {

                if (snapshot != null) {

                    if (!snapshot.isEmpty) {

                        titleTextFromFB.clear()
                        noteTextFromFB.clear()
                        imageFromFB.clear()

                        val documents = snapshot.documents
                        for (document in documents) {

                            val userEmail = document.get("userEmail") as String
                            val noteTitle = document.get("noteTitle") as String
                            val yourNote = document.get("yourNote") as String
                            val downloadUrl = document.get("downloadUrl") as String
                            val timestamp = document.get("date") as Timestamp
                            val date = timestamp.toDate()

                            titleTextFromFB.add(noteTitle)
                            imageFromFB.add(downloadUrl)
                            noteTextFromFB.add(yourNote)

                            adapter!!.notifyDataSetChanged()

                        }
                    }
                }

            }


        }


    }

    fun itemDelete(data: Any) {

        db.collection("Notes").document().delete().addOnSuccessListener {


        }

            .addOnFailureListener { exception ->

                Toast.makeText(applicationContext, exception.localizedMessage.toString(), Toast.LENGTH_LONG).show()
            }
    }


}

Answer 1

此代码将不起作用:

   db.collection("Notes").document().delete().addOnSuccessListener {

db.collection("Notes").document()调用创建对新文档的引用，然后将其删除。所以什么也没发生。
您需要确定用户单击的文档的ID，并将其传递给 document(...)调用。这样可以为正确的文档提供 DocumentReference，以便 delete()调用将删除该文档。
确定用户单击的文档ID的关键在以下代码中:

adapter = NoteAdapter(titleTextFromFB, imageFromFB, noteTextFromFB, object: NoteAdapter.onClick{
    override fun onItemClickListener(v: View, pos: Int, data: Any) {
        when(v.id){
            R.id.delete -> itemDelete(data)
        }
    }
})

您将需要从以下参数之一确定ID: v， post或 data。我通常通过在适配器或 Activity 中保留文档ID或 DocumentSnapshot对象的列表，然后按其位置/索引查找单击的项目来完成此操作。
因此，在 getDataFromFirestore函数中，将快照添加到您在 Activity 类中定义为字段的列表中:

// in your activity, declare a list;
var mDocuments: List<DocumentSnapshot>? = null

// Then in getDataFromFirestore store that list
...
mDocuments = snapshot.documents;
val documents = snapshot.documents
for (document in documents) {
    ...
}
...

// And use it when calling itemDelete:
adapter = NoteAdapter(titleTextFromFB, imageFromFB, noteTextFromFB, object: NoteAdapter.onClick{
    override fun onItemClickListener(v: View, pos: Int, data: Any) {
        when(v.id){
            R.id.delete -> itemDelete(mDocuments[pos])
        }
    }
})

// To then finally delete the document by its ID
fun itemDelete(doc: DocumentSnapshot) {
    db.collection("Notes").document(doc.Id).delete()
}