错误"Required:String Found:String?" Kotlin和Android Studio [英] Error "Required:String Found:String?" Kotlin and Android Studio

问题描述

正如标题所示，我在"var myNote = Note(id(标题，标题，说明，ServerValue.TIMESTAMP)")行的"id"下获得红色下划线 错误必需:找到的字符串:字符串?" Kotlin和Android Studio

As the title suggests Im getting a red underline under "id" on the line "var myNote = Note(id, title, note, ServerValue.TIMESTAMP)" Error "Required:String Found:String?" Kotlin and Android Studio

class MainActivity : AppCompatActivity() {
    var mRef:DatabaseReference? = null

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

        val database = FirebaseDatabase.getInstance()
        mRef = database.getReference("Notes")

        add_new_note.setOnClickListener {
            showDialogAddNote()
        }
    }

    fun showDialogAddNote() {
        val alertBuilder = AlertDialog.Builder(this)

        val view = layoutInflater.inflate(R.layout.add_note, null)

        alertBuilder.setView(view)

        val alertDialog = alertBuilder.create()
        alertDialog.show()

        view.btnSaveNote.setOnClickListener {
            val title = view.etTitle.text.toString()
            val note = view.etNote.text.toString()

            if (title.isNotEmpty() && note.isNotEmpty()) {
                var id = mRef!!.push().key

                var myNote = Note(id, title, note, ServerValue.TIMESTAMP)
                mRef!!.child(id).setValue(myNote)
                alertDialog.dismiss()    
            } else {
                Toast.makeText(this, "Empty", Toast.LENGTH_LONG).show()
            }
        }
    }
}

这是我的Notes.kt类

Here is my Notes.kt class

package com.example.gearoidodonovan.books

import java.util.*

class Note (var id:String, var title:String, var note:String, var timestamp: MutableMap<String, String>) {
}

推荐答案

科特林迫使您对可空性保持高度的意识.

Kotlin forces you to be hyper-conscious about nullability.

您的Note实体说它需要一个不可为null的id:String，显然，mRef!!.push().key返回一个String?表示它是可为null的字符串.您可以通过双击将其修复，例如mReff!!.push().key!!

Your Note entity say its requires a non-nullable id:String, and apparently, mRef!!.push().key returns a String? meaning it's a nullable String. You can fix this by double-banging it , i.e. mReff!!.push().key!!

另一个提示是ALT+ENTER这些与Kotlin相关的错误，它将为您提供双重效果.

Another tip is to ALT+ENTER these Kotlin related errors, it'll provide the double-bang for you.

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