[英]Can't set Text of TextView
我想将TextView
的文本更改为活动用户的任何用户名,但方法updateUI()
始终返回此错误:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.cocko.industries.einkaufshelfer.shopper, PID: 18704
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.cocko.industries.einkaufshelfer.shopper/com.cocko.industries.einkaufshelfer.shopper.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.cocko.industries.einkaufshelfer.shopper.MainActivity.updateUI(MainActivity.java:203)
at com.cocko.industries.einkaufshelfer.shopper.MainActivity.onCreate(MainActivity.java:76)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
所以有什么问题? 在我看来好像找不到TextView
,因此为空。 但为什么? 我该如何解决? 您可以在下面找到带有onCreate
和updateUI
方法的MainActivity
类以及我使用的片段。
public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {
private DrawerLayout drawer;
private NavigationView nav_view;
private FirebaseAuth mAuth;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mAuth = FirebaseAuth.getInstance();
nav_view = findViewById(R.id.nav_view);
nav_view.setNavigationItemSelectedListener(this);
drawer = findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar, R.string.nav_drawer_open, R.string.nav_drawer_close);
drawer.addDrawerListener(toggle);
toggle.syncState();
try {
Intent intent = getIntent();
if (intent.getStringExtra("activity").equals("register")) {
getSupportFragmentManager().beginTransaction().replace(R.id.framgment_container, new UserprofileFragment()).commit();
}
} catch (NullPointerException noIntentExtra) {
getSupportFragmentManager().beginTransaction().replace(R.id.framgment_container, new AssignmentsFragment()).commit();
}
if (mAuth.getCurrentUser() != null){
updateUI();
}
}
而updateUI
函数如下。
public void updateUI() {
TextView textView = findViewById(R.id.textview_assignemntsheader);
textView.setText("Test");
}
这是我的片段的布局,即fragment_assignments.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"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/textview_assignemntsheader"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
android:text="@string/textview_assigmentsHeader"
android:textAlignment="center"
android:textAppearance="@style/TextAppearance.AppCompat.Display1"
android:textStyle="bold"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ScrollView
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_marginStart="8dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="8dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textview_assignemntsheader">
<LinearLayout
android:id="@+id/linearlayout_assignments"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
</LinearLayout>
</ScrollView>
</androidx.constraintlayout.widget.ConstraintLayout>
我的活动的布局是activity_main.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/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context=".MainActivity"
tools:openDrawer="start">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<androidx.appcompat.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="@color/colorPrimary"
android:elevation="4dp"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />
<FrameLayout
android:id="@+id/framgment_container"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
<com.google.android.material.navigation.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
app:headerLayout="@layout/nav_header"
app:menu="@menu/menu" />
</androidx.drawerlayout.widget.DrawerLayout>
你在 MainActivity 中找不到你的 textView 因为它不在 main_activity.xml 中,所以 updateUI 应该在 UserProfile Fragment 中。
在OnCreateView
尝试这个 :
View view = inflater.inflate(R.layout.fragment_assignments, container,false);
TextView text=view.findViewById(R.id.textview_assignemntsheader);
你在哪里膨胀 fragment_assignments.xml? 在这一行中,您膨胀 main_activity.xml
setContentView(R.layout.activity_main);
但是,textview_assignemntsheader 位于另一个 XML 文件中,无法找到它并返回 null。 findViewById 将仅在膨胀视图中搜索 ID。 将 UpdateUI 函数移动到 UserProfile(其中 fragment_assignments.xml 被膨胀)
在您的MainActivity
您正在膨胀没有TextView
的activity_main
布局。 因此,您在尝试查找TextView
并为其分配一些文本时遇到NullPointerException
。
在MainActivity
类的onCreate
方法中,尝试将文本设置为不存在或未膨胀的TextView
。 fragment_assignments.xml
布局可能会在您的片段中膨胀,因此您会在片段中找到布局引用。
看起来您想将身份验证信息传递给您的片段并在那里设置一些值。 在这种情况下,您可以在执行片段事务时使用包传递信息。
因此,您的活动中的片段交易可能具有以下功能。
public void launchAssignmentFragment() {
AssignmentFragment frag = new AssignmentFragment();
Bundle bundle = new Bundle();
if (mAuth.getCurrentUser() != null) {
bundle.putBoolean("auth", true);
} else {
bundle.putBoolean("auth", false);
}
// set Arguments to be passed to the fragment
frag.setArguments(bundle);
// Now load the fragment
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
transaction.replace(R.id.fragment_container, frag);
transaction.addToBackStack(null);
transaction.commit();
}
现在从你的片段的onCreateView
,你可以做这样的事情。
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout. fragment_assignments, parent, false);
TextView tv = rootView.findViewById(R.id.textview_assignemntsheader);
// Get the passed-in value here
boolean auth = getArguments().getBoolean("auth");
if (auth) tv.setText("Success");
else tv.setText("Fail");
return rootView;
}
最后,按如下方式更新MainActivity
的onCreate
。
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mAuth = FirebaseAuth.getInstance();
nav_view = findViewById(R.id.nav_view);
nav_view.setNavigationItemSelectedListener(this);
drawer = findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar, R.string.nav_drawer_open, R.string.nav_drawer_close);
drawer.addDrawerListener(toggle);
toggle.syncState();
try {
Intent intent = getIntent();
if (intent.getStringExtra("activity").equals("register")) {
getSupportFragmentManager().beginTransaction().replace(R.id.framgment_container, new UserprofileFragment()).commit();
}
} catch (NullPointerException noIntentExtra) {
getSupportFragmentManager().beginTransaction().replace(R.id.framgment_container, new AssignmentsFragment()).commit();
}
if (mAuth.getCurrentUser() != null){
launchAssignmentFragment(); // launch the fragment maybe?
}
}
我希望这有帮助!
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