kotlin.TypeCastException: null 不能转换为非 null 类型 com.midsizemango.databasekotlin.Note
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【中文标题】kotlin.TypeCastException: null 不能转换为非 null 类型 com.midsizemango.databasekotlin.Note【英文标题】：kotlin.TypeCastException: null cannot be cast to non-null type com.midsizemango.databasekotlin.Note 【发布时间】：2016-10-23 06:33:50 【问题描述】：我正在尝试在 Kotlin 中编写我的应用程序，但是当我在 EXTRA_NOTE 打开 EditNoteActivity 时，我无法将 null 强制转换为非 null 类型，并且应用程序强制停止。
非常感谢任何帮助
代码：
class EditNoteActivity : AppCompatActivity()
var note: Note? = null
private val editNote: TextView? = null
private val fabdrwble: Boolean? = null
private val notesData: MutableList<Note>? = null
private var databaseHelper: DatabaseHelper? = null
private val save: Boolean? = null
private var saveButton: FloatingActionButton? = null
private val tint: ColorStateList? = null
internal var mRowId: Long? = null
internal var spinner: Spinner? = null
internal var spinnertext: String? = null
internal var fav: Int = 0
internal var mSharedFromIntentFilter = false
internal var editTitle: EditText? = null
internal var editContent: EditText? = null
internal var inputlayoutTitle: TextInputLayout? = null
internal var inputlayoutContent: TextInputLayout? = null
override fun onCreate(savedInstanceState: Bundle?)
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_edit_note)
var toolbar = findViewById(R.id.toolbar_edit) as Toolbar?
setSupportActionBar(toolbar)
if (supportActionBar != null)
supportActionBar!!.setDisplayHomeAsUpEnabled(true)
databaseHelper = DatabaseHelper(applicationContext)
inputlayoutTitle = findViewById(R.id.inputlayoutTitle) as TextInputLayout?
inputlayoutContent = findViewById(R.id.inputlayoutContent) as TextInputLayout?
editTitle = findViewById(R.id.note_title) as EditText
editContent = findViewById(R.id.note_content) as EditText?
val bundle = intent.extras
val s = bundle.getString("edit")
if (s == "add")
window.setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_VISIBLE)
else if (s == "editv")
window.setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_HIDDEN)
note = intent.getSerializableExtra(EXTRA_NOTE) as Note
if (note != null)
editTitle?.setText(note!!.getTitle())
editContent?.setText(note!!.getContent())
else
note = Note()
//note.setUpdatedAt(new Date());
saveButton = findViewById(R.id.add_edit_button) as FloatingActionButton?
saveButton!!.setOnClickListener
if (isNoteFormOk)
setNoteResult()
finish()
else
validateNoteForm()
var ll = findViewById(R.id.llmain) as LinearLayout?
var ll1 = findViewById(R.id.ll1) as LinearLayout?
/*if(note.getColor() == Color.TRANSPARENT)
selectedColor = preselect;
else
selectedColor = note.getColor();
getWindow().addFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
systemBarTintManager = new SystemBarTintManager(this);
systemBarTintManager.setStatusBarTintEnabled(true);
ll.setBackgroundColor(selectedColor);
ll1.setBackgroundColor(selectedColor);
toolbar.setBackgroundColor(note.getColor());
systemBarTintManager.setStatusBarTintColor(selectedColor);*/
override fun onResume()
super.onResume()
override fun onOptionsItemSelected(item: MenuItem): Boolean
when (item.itemId)
android.R.id.home ->
onBack()
return true
/*
case R.id.speech:
try
displaySpeechRecognizer();
catch (ActivityNotFoundException e)
Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("https://market.android.com/details?id=com.google.android.googlequicksearchbox"));
startActivity(browserIntent);
return true;*/
else -> return super.onOptionsItemSelected(item)
private fun displaySpeechRecognizer()
val intent = Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH)
intent.putExtra(RecognizerIntent.EXTRA_LANGUAGE_MODEL, RecognizerIntent.LANGUAGE_MODEL_FREE_FORM)
startActivityForResult(intent, SPEECH_REQUEST_CODE)
override fun onActivityResult(requestCode: Int, resultCode: Int,
data: Intent)
if (requestCode == SPEECH_REQUEST_CODE && resultCode == Activity.RESULT_OK)
val results = data.getStringArrayListExtra(RecognizerIntent.EXTRA_RESULTS)
val spokenText = results[0]
editContent?.setText(spokenText)
if (requestCode == RequestResultCode.REQUEST_CODE_ADD_NOTE)
if (resultCode == Activity.RESULT_OK)
addNote(data)
private val isNoteFormOk: Boolean
get()
val title = editTitle?.text.toString()
return !(title == null || title.trim it <= ' ' .length == 0)
private fun validateNoteForm()
var msg: String? = null
if (isNullOrBlank(editTitle?.text.toString()))
msg = "Title Required"
inputlayoutTitle?.error = "Title is Missing"
if (msg != null)
Toast.makeText(applicationContext, msg, Toast.LENGTH_LONG).show()
private fun setNoteResult()
note!!.setTitle(editTitle?.text.toString().trim it <= ' ' )
note!!.setContent(editContent?.text.toString().trim it <= ' ' )
//note.setUpdatedAt(new Date());
val intent = Intent()
intent.putExtra(EXTRA_NOTE, note)
setResult(Activity.RESULT_OK, intent)
//addNote(intent);
Toast.makeText(this@EditNoteActivity, "Note Saved.", Toast.LENGTH_LONG).show()
private fun onBack()
if (isNoteFormOk)
if (editTitle?.text.toString() == note!!.getTitle() && editContent?.text.toString() == note!!.getContent())
setResult(Activity.RESULT_CANCELED, Intent())
finish()
else
AlertDialog.Builder(this@EditNoteActivity)
.setTitle("Save")
.setMessage("Do You Want to Save Note")
.setPositiveButton("SAVE") dialog, which ->
setNoteResult()
finish()
.setNegativeButton("CANCEL") dialog, which ->
setResult(Activity.RESULT_CANCELED, Intent())
finish()
.show()
else
setResult(Activity.RESULT_CANCELED, Intent())
finish()
private fun addNote(data: Intent)
val note = data.getSerializableExtra(EXTRA_NOTE) as Note
val noteId = databaseHelper!!.createNote(note)
note.setId(noteId)
override fun onBackPressed()
onBack()
val intentHome = Intent(this@EditNoteActivity, MainActivity::class.java)
intentHome.flags = Intent.FLAG_ACTIVITY_CLEAR_TOP
intentHome.putExtra(EXTRA_NOTE, note)
setResult(Activity.RESULT_OK, intentHome)
companion object
private val EXTRA_NOTE = "EXTRA_NOTE"
private val SPEECH_REQUEST_CODE = 0
fun isNullOrBlank(str: String?): Boolean
return str == null || str.trim it <= ' ' .length == 0
日志：
java.lang.RuntimeException: Unable to start activity ComponentInfo com.midsizemango.databasekotlin/com.midsizemango.databasekotlin.EditNoteActivity: kotlin.TypeCastException: null cannot be cast to non-null type com.midsizemango.databasekotlin.Note at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) at android.app.ActivityThread.access$800(ActivityThread.java:144) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) Caused by: kotlin.TypeCastException: null cannot be cast to non-null type com.midsizemango.databasekotlin.Note at com.midsizemango.databasekotlin.EditNoteActivity.onCreate(EditNoteActivity.kt:82) at android.app.Activity.performCreate(Activity.java:5933) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) at android.app.ActivityThread.access$800(ActivityThread.java:144) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:694)
【问题讨论】：
【参考方案1】：在这一行：
note = intent.getSerializableExtra(EXTRA_NOTE) as Note
Note 是 non-null type，因此对其的强制转换会触发空检查。由于之后您要手动比较 note 和 null，因此您的意思可能是 safe cast operator，如果表达式不是右侧指定的类型，则生成 null：
note = intent.getSerializableExtra(EXTRA_NOTE) as? Note
【讨论】：
就像 Swift 一样！ @Dante Kotlin 初始版本：2011 年，Swift 初始版本：2014 年。我认为情况正好相反；） 它的真棒答案 我在想，为什么编译器没有意识到这个问题。 因为它不知道编译时的值。只有在运行时才会检测到空值。以上是关于kotlin.TypeCastException: null 不能转换为非 null 类型 com.midsizemango.databasekotlin.Note的主要内容，如果未能解决你的问题，请参考以下文章