android - 从另一个 Activity 将字符串推送到数组

Question

my aplication

我有 2 个 Activity ，第一个是 CategoryActivity，第二个是 QuestionActivity。在 CategoryActivity 中，我有一个列出类别的 recyclerview，在 Category Activity 中，我有一个数组。当我单击 eksterior 时，它将转到 questionActivity，当我单击提交时，它将返回到 CategoryActivity 并将数据发送到 CategotyActivity。发送的数据被输入到数组中，所以数组将是这样的: array[] = {“1”};然后我点击recyclerview中的第二个item是interior，然后它会再次进入QuestionActivity，当我点击提交时，它会将数据发送到CategoryActivity并将其添加到之前的数组中，所以数组将是这样的:array [] = {“1”，“1”}；依此类推，直到 recyclerview 上的项目用完。我试过这样:

QuestionActivity.kt

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

    button_save.setOnClickListener(){
        val intent = Intent(this@ResultActivity, KategoriActivity::class.java)
        intent.putExtra(KategoriActivity.Companion.ARRAY, "1")
        startActivity(intent)
    }
}

CategoryActivity.kt

var list = arrayOf(intent.getStringExtra(ARRAY))
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_category)
    Toast.makeText(this@KategoriActivity, ""+ list, Toast.LENGTH_SHORT).show()


}
companion object {
    val ARRAY = "array"

}

override fun onBackPressed() {
    Toast.makeText(this@KategoriActivity, ""+ list, Toast.LENGTH_SHORT).show()
    if (list.size == kategoriDatas!!.size){
        onBackPressed()
    } else {
        val builder = AlertDialog.Builder(this)
        builder.setMessage("You Must Finish All The Category")

        // add a button
        builder.setPositiveButton("OK", null)

        // create and show the alert dialog
        val dialog = builder.create()
        dialog.show()
    }
    }

问题是当我打开类别 Activity 时，应用程序停止了，并且日志显示 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Intent .getStringExtra(java.lang.String)' 在空对象引用上

数据无法推送到数组，请帮帮我

Answer 1

您只能在 Activity 创建后获取 Intent 。为了确保这一点，最好将将从 Intents 获取额外内容的代码放在 onCreate 中。

像这样:

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_category)
    Toast.makeText(this@KategoriActivity, ""+ list, Toast.LENGTH_SHORT).show()
    var list = arrayOf(intent.getStringExtra(ARRAY))
}

如果你想要一个包含信息的 Application 类:

class MyApplication : Application(){
var list = emptyArray<String>()

  override fun onCreate() {
    super.onCreate()
  }
}

在您的 Activity 中使用它:

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_category)
    Toast.makeText(this@KategoriActivity, ""+ list, Toast.LENGTH_SHORT).show()
    var list = (application as MyApplication).list
   // you can than use it to update or retrieve values from it
}