Question

主要活动：

val turminha : Turma = this.abrirArquivo()

    recycler_view.layoutManager = LinearLayoutManager(this)
    recycler_view.adapter = AlunoAdapter(this,turminha.alunos)

    floatingActionButton.setOnClickListener({
        val i = Intent(this, ActivityAddAluno::class.java)
        i.putExtra("turma", turminha)
        startActivity(i)
    })

ActivityAddAluno

class ActivityAddAluno : AppCompatActivity() {
    var i = getIntent()
    private var turma = i.getSerializableExtra("turma") as Turma

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

        mBtnSalvarAluno.setOnClickListener{
            var name = mEdtNomeAluno.text.toString()
            var matricula = mEdtMatriculaAluno.text.toString()
            toast("Nome: $name \n," +
                "Matricula: $matricula")

            turma.addAluno(Aluno(name, matricula))
        }
    }

Aluno班 Aluno类：Serializable {

var disciplinas: ArrayList<Disciplina>? = null
    private set
var nome: String? = null
var matricula: String? = null

constructor() {
    disciplinas = ArrayList()
}

constructor(nome: String, matricula: String) {
    this.nome = nome
    this.matricula = matricula
    disciplinas = ArrayList()
}

类Turma

class Turma() : Serializable {

    val alunos: ArrayList<Aluno>

    init {
        alunos = ArrayList()
    }

    fun addAluno(aluno: Aluno) {
        alunos.add(aluno)
    }

当我尝试访问在浮动按钮中传递我的Turma对象的其他活动时，应用程序停止工作。 Logcat说问题出在代码部分：

var i = getIntent()
private var turma = i.getSerializableExtra("turma") as Turma

logcat的：

FATAL EXCEPTION: main
Process: com.example.thial.estudandokotlin, PID: 3428
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.thial.estudandokotlin/com.example.thial.estudandokotlin.ActivityAddAluno}:
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.Serializable android.content.Intent.getSerializableExtra(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2548)

我该如何解决这个问题？

Answer 1

实际上，根据您的日志消息，您的问题就在这里。

var i = getIntent()
private var turma = i.getSerializableExtra("turma") as Turma

此处值“i”为空，并且在此之上您尝试使用getSerializableExtra()字符串。

您在ActivityAddAluno类中调用此行的确切位置是什么？它必须位于onCreate函数内，而不是在构造函数中。（按照约书亚的说法）

 override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        //...
        var i = getIntent()
       if(i!=null)
       {
       private var turma = i.getSerializableExtra("turma") as Turma
       }

  }

以下是Switching between Activities along with data using Kotlin

示例之一

尝试访问其他活动时应用崩溃

1 个答案: