我尝试设置TextView值时出现NullPointerException

Question

我有问题。为什么当我尝试将值设置为TextView时，调试器显示NullPointerException吗？

这是我的调试器中的日志：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: bjd.adrian.sebaclicker, PID: 7258
java.lang.RuntimeException: Unable to start activity ComponentInfo{bjd.adrian.sebaclicker/bjd.adrian.sebaclicker.Views.ClickerView}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2927)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2988)
    at android.app.ActivityThread.-wrap14(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1631)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6682)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
    at android.support.v7.app.AppCompatDelegateImpl.<init>(AppCompatDelegateImpl.java:249)
    at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:182)
    at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:520)
    at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:191)
    at bjd.adrian.sebaclicker.Views.ClickerView.setScore(ClickerView.kt:33)
    at bjd.adrian.sebaclicker.Presenters.ClickerPresenter.getScoreandSetInTextView(ClickerPresenter.kt:19)
    at bjd.adrian.sebaclicker.Views.ClickerView.onCreate(ClickerView.kt:22)
    at android.app.Activity.performCreate(Activity.java:6942)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2880)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2988) 
    at android.app.ActivityThread.-wrap14(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1631) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6682) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1520) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1410) 

这是我的ClickerView：

class ClickerView : AppCompatActivity()
{

    val context: Context = this@ClickerView

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

        val clickerPresenter = ClickerPresenter(context)
        clickerPresenter.getScoreandSetInTextView()

    }

    fun setScore(score: Int)
    {
        var score = score
        Log.v("CLICKER VIEW", "SCORE: "+score)

        var scoreS = score.toString()

        val scoreTV: TextView = findViewById(R.id.scoreTV)
        scoreTV.text = scoreS
    }


}

这是我的ClickerPresenter：

class ClickerPresenter(contextP: Context)
{
    val context = contextP

    fun getScoreandSetInTextView()
    {
        val ClickerView = ClickerView()
        val ClickerModel = ClickerModel(context)

        var score = ClickerModel.getScore()
        ClickerView.setScore(score)

    }
}

这是我的ClickerModel：

class ClickerModel(contextP: Context)
{

    var context = contextP

    fun getScore() : Int
    {
        var prefs: SharedPreferences? = null
        prefs = context.getSharedPreferences("PREFS", 0)

        var score = prefs.getInt("sebolary", 1)

        Log.v("ClickerModel", "SCORE: "+score.toString())

        return score
    }

}

变量score不是 null （我在日志中对此进行了检查）。

我当时正在互联网上寻求解决此问题的方法，但是我什么也没发现。

这是.xml文件：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".Views.ClickerView">

<ImageView
        android:src="@drawable/background"
        android:layout_width="998dp"
        android:layout_height="993dp"
        android:id="@+id/backgroungIV" android:layout_marginTop="8dp"
        app:layout_constraintTop_toTopOf="parent" app:layout_constraintStart_toStartOf="parent"
        android:layout_marginStart="8dp" app:layout_constraintEnd_toEndOf="parent" android:layout_marginEnd="8dp"
        android:layout_marginBottom="9dp" app:layout_constraintBottom_toBottomOf="parent"
        android:adjustViewBounds="false" android:cropToPadding="true" app:layout_constraintHorizontal_bias="0.526"
        app:layout_constraintVertical_bias="0.893"/>
<Button
        android:layout_width="143dp"
        android:background="@drawable/seba"
        android:layout_height="200dp"
        android:id="@+id/sebaBTT" android:layout_marginTop="144dp"
        app:layout_constraintTop_toTopOf="parent" app:layout_constraintStart_toStartOf="parent"
        android:layout_marginStart="120dp"/>
<Button
        android:layout_width="100dp"
        android:layout_height="54dp"
        android:id="@+id/shopBTT" android:layout_marginTop="16dp"
        app:layout_constraintTop_toTopOf="parent" app:layout_constraintStart_toStartOf="parent"
        android:layout_marginStart="284dp"
        android:background="@drawable/shoppingcart"
/>
<TextView
        android:text="Sebolary: "
        android:layout_width="74dp"
        android:layout_height="22dp"
        android:id="@+id/textView" android:layout_marginTop="44dp"
        app:layout_constraintTop_toTopOf="parent" app:layout_constraintStart_toStartOf="parent"
        android:layout_marginStart="16dp" android:textSize="18sp"
        app:layout_constraintBottom_toBottomOf="@+id/scoreTV" app:layout_constraintVertical_bias="0.0"/>
<TextView
        android:text="0000"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/scoreTV" android:textSize="18sp"
        android:layout_marginTop="8dp"
        app:layout_constraintTop_toTopOf="parent" android:layout_marginBottom="8dp"
        app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintVertical_bias="0.068"
        app:layout_constraintStart_toEndOf="@+id/textView" android:layout_marginStart="16dp"/>
<Button
        android:text="Osignięcia"
        android:layout_width="390dp"
        android:layout_height="56dp"
        android:id="@+id/achevementsBTT" android:layout_marginTop="516dp"
        android:background="@drawable/achevementsbar"
        app:layout_constraintTop_toTopOf="parent" app:layout_constraintStart_toStartOf="parent"
/>
<Button
        android:text="Resetuj licznik"
        android:layout_width="105dp"
        android:layout_height="62dp"
        android:id="@+id/resetBTT"
        android:background="@drawable/background"
        android:layout_marginTop="432dp"
        app:layout_constraintTop_toTopOf="parent" app:layout_constraintStart_toStartOf="parent"
        android:layout_marginStart="32dp"/>
<Button
        android:text="Zapisz wynik"
        android:layout_width="105dp"
        android:layout_height="62dp"
        android:id="@+id/saveBTT" android:layout_marginTop="440dp"
        android:background="@drawable/background"
        app:layout_constraintTop_toTopOf="parent" app:layout_constraintEnd_toEndOf="parent"
        android:layout_marginEnd="32dp"/>

Answer 1

ClickerView是一项活动：

class ClickerView : AppCompatActivity()

但是您要自己实例化它：

val ClickerView = ClickerView()

，然后在其上调用方法：

ClickerView.setScore(score)

您不应该自己实例化Activity类-它们对您需要Activity进行的任何操作都不会有好处。

常见的MVP方法是Presenter持有对其View的引用-将ClickerView作为ClickerPresenter的参数。