如何在Android Studio中解决此文本视图错误？

Question

我使用Android Studio和Kotlin创建了一个应用程序。当我想更改应用程序的主题或更改应用程序的语言时，都会导致该应用程序崩溃，这两个错误都需要重新启动仪表板活动。我不知道如何解决：

这里是代码：

1-在dashboard.kt中：

class DashboardActivity : AppCompatActivity() {
private lateinit var storageReference: StorageReference
private lateinit var databaseReference: DatabaseReference
private lateinit var user: User
private lateinit var uid: String
private var toolbar: Toolbar? = null
private var viewPager: ViewPager? = null
private var tabLayout: TabLayout? = null
private var exploreFragment: ExploreFragment? = null
private var flightsFragment: FlightsFragment? = null
private var travelFragment: TravelFragment? = null
private lateinit var auth: FirebaseAuth
private lateinit var binding: ActivityDashboardBinding
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    auth = FirebaseAuth.getInstance()
    uid = auth.currentUser?.uid.toString()
    databaseReference = FirebaseDatabase.getInstance().getReference("Users")
    if (uid.isNotEmpty()){
        getUserData()
    }
private fun getUserData() {
    val scoresRef = Firebase.database.getReference("Users")
    scoresRef.child(uid).addValueEventListener(object : ValueEventListener {
        @SuppressLint("SetTextI18n")
        override fun onDataChange(snapshot: DataSnapshot) {
            user = snapshot.getValue(User::class.java)!!
            val name = findViewById<TextView>(R.id.tvFirstNameAndLastName)
            val phoneNumber = findViewById<TextView>(R.id.tvPhoneNumber)
            name.text = user.name+" "+user.lastName
            phoneNumber.text = user.phoneNumber
            getUserProfile()
        }
        override fun onCancelled(error: DatabaseError) {
            finish()
        }
    })
}

通过删除这两行：

name.text = user.name+" "+user.lastName
        phoneNumber.text = user.phoneNumber

一切正常，我在两行上使用了这两行，从firebase检索数据，当我向他们展示时，它可以正常工作在导航视图中的NAV标题中，但是在更改应用程序主题/语言应用程序崩溃和Android Studio中显示了LogCat中的此错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at af.azdreams.myconquer.DashboardActivity$getUserData$1.onDataChange(DashboardActivity.kt:293)

Dashboard.xml：

<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawerLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".DashboardActivity">
<androidx.coordinatorlayout.widget.CoordinatorLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <com.google.android.material.appbar.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="@color/Orange"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent">
            <ImageButton
                android:id="@+id/btnSearchUsers"
                android:layout_width="wrap_content"
                android:background="#0000"
                android:layout_height="wrap_content"
                app:srcCompat="@drawable/icon_search"
                android:contentDescription="@string/todo" />
        </androidx.appcompat.widget.Toolbar>
        <com.google.android.material.tabs.TabLayout
            app:tabTextAppearance="@style/MineCustomTabText"
            android:id="@+id/tabLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"/>
    </com.google.android.material.appbar.AppBarLayout>

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="com.google.android.material.appbar.AppBarLayout$ScrollingViewBehavior" />
</androidx.coordinatorlayout.widget.CoordinatorLayout>
<com.google.android.material.navigation.NavigationView
    android:id="@+id/navView"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:layout_gravity="start"
    app:headerLayout="@layout/header"
    app:itemTextAppearance="@style/menu"
    app:menu="@menu/nav_menu" />
</androidx.drawerlayout.widget.DrawerLayout>

Heaader.xml：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="150dp"
android:id="@+id/header"
android:background="@color/Orange">

<de.hdodenhof.circleimageview.CircleImageView
    android:id="@+id/circleImageView"
    android:layout_width="67dp"
    android:layout_height="67dp"
    android:layout_marginStart="5dp"
    app:civ_border_width="1dp"
    android:src="@drawable/profile"
    app:civ_border_color="@color/White"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.047"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.213" />

<TextView
    android:id="@+id/tvFirstNameAndLastName"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="6dp"
    android:layout_marginTop="13dp"
    android:text=""
    android:textColor="@color/White"
    android:textSize="15dp"
    android:textStyle="bold"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.05"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/circleImageView" />

<TextView
    android:id="@+id/tvPhoneNumber"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="6dp"
    android:text=""
    android:textColor="@color/Black"
    android:textSize="13dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.05"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/tvFirstNameAndLastName"
    app:layout_constraintVertical_bias="0.0" />
</androidx.constraintlayout.widget.ConstraintLayout>

当我在Google上搜索此错误时，人们也遇到了相同的问题，我尝试了Thier thier thier但是应用程序也崩溃了:(

如果您知道正确的解决方案，请帮助我。

感谢谁在帮助我。

Answer 1

您尚未将任何布局设置为活动的内容视图，在ongreate方法中。

通过调用setContentView将布局设置为您的活动，

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

---

以访问navigationView's header，您首先需要获得其> Headerview然后您可以通过使用findViewById获得视图内部

val navigationView = findViewById<NavigationView>(R.id.navView)
val header: View = navigationView.getHeaderView(0)
val name = header.findViewById<TextView>(R.id.tvFirstNameAndLastName)