SupportfragmentManager变成null android kotlin

我试图从onPostExecute启动一个dialogFragment，但由于某种原因supportFragmentManager返回null。 我试图从主要活动和其他片段启动dialogFragment，它完美的作品，但我不能从AsyncTask启动它。 这是AsyncTask： –

class SubscribeTask: AsyncTask<Void, Void, Void> { var mContext: Context var mTextView_temp: TextView var mTextView_humidity: TextView var mWeather_image: ImageView var mMessage: JsonObject var mResult = JsonObject() var mTemp: String = "" var mHumidity: String = "" var mLdr: Boolean = true var mRain: Boolean = false var mWeather: Int = 0 var tester: Boolean = false var mFire: Boolean = false constructor(context: Context, textView_temp: TextView, textView_humidity: TextView, weather_image: ImageView, message: PNMessageResult){ mContext = context mMessage = message.message.asJsonObject mTextView_temp = textView_temp mTextView_humidity = textView_humidity mWeather_image = weather_image } override fun doInBackground(vararg p0: Void?): Void? { if (mMessage.has("pi")){ mResult = mMessage.getAsJsonObject("pi") mTemp = mResult.get("temp").asString mHumidity = mResult.get("humidity").asString mLdr = mResult.get("ldr").asBoolean mRain = mResult.get("rain").asBoolean mFire = mResult.get("fire").asBoolean tester = true if(mRain){ mWeather = R.drawable.rainy }else if(mLdr){ mWeather = R.drawable.suny }else{ mWeather = R.drawable.cloudyy } } return null } override fun onPostExecute(result: Void?) { if(tester) { mTextView_temp.text = mTemp mTextView_humidity.text = mHumidity mWeather_image.setImageResource(mWeather) if(mFire){ MainActivity().showAlertDialog("Fire", "There might be a fire in the house", R.drawable.house_fire, "Stop Alarm") } } } } 

这是showAlertDialog（）函数： –

 fun showAlertDialog(title: String, content: String, imageid: Int, button: String){ val fm = supportFragmentManager val alertDialogFragment = AlertFragment(title, content, imageid, button).newInstance(title, content, imageid, button) alertDialogFragment.show(fm, "fragment_alert") } 

这是dialogFragment： –

 class AlertFragment(val mTitle: String, val mContent: String, val mImageId: Int, val mButton: String) : DialogFragment() { fun newInstance(title: String, content: String, imageid: Int, button: String): AlertFragment { val alertfrag = AlertFragment(title, content, imageid, button) val args = Bundle() args.putString("title", title) alertfrag.arguments = args return alertfrag } override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? { // Inflate the layout for this fragment return inflater!!.inflate(R.layout.fragment_alert, container, false) } override fun onViewCreated(view: View?, savedInstanceState: Bundle?) { super.onViewCreated(view, savedInstanceState) title.text = mTitle alertContent.text = mContent alertImageId.setImageResource(mImageId) alertButton.text = mButton } } 

有人可以帮帮我吗。 Java中的答案也没关系。

Answer 1

你可以使用观察者模式。

创建一个这样的界面

 interface myExecListener { fun onFinish(title: String, content: String, imageid: Int, button: String) } 

将此行添加到SubscribeTask

 class SubscribeTask: AsyncTask<Void, Void, Void>() { var listener: myExecListener? = null fun exec(listener: myExecListener){ this.listener = listener this.execute() } override fun doInBackground(vararg params: Void?): Void? { return null } override fun onPostExecute(result: Void?) { super.onPostExecute(result) listener?.onFinish("Fire", "There might be a fire in the house", 333, "Stop Alarm") } } 

并在你的活动中执行

 SubscribeTask().exec(object : myExecListener{ override fun onFinish(title: String, content: String, imageid: Int, button: String) { println("Observer triggered") showAlertDialog(title, content, imageid, button) } }) 

Answer 2

在你的postExecute函数中有以下代码：

 MainActivity().showAlertDialog(...) 

这创建了一个新的活动对象，这绝对不是应该做的。 由于该对象是新创建的，并且没有被android正确初始化，像supportFragmentManager这样的内部对象没有被初始化，导致你看到的是null 。