FAB按钮与底部导航视图一起使用时出错

Question

我有一个底部导航视图，在底部导航视图的中心有一个浮动操作按钮。当单击底部导航视图项时，我启动片段，当单击浮动操作按钮时，我开始一个活动。碎片加载正确，但当我点击fab按钮时，有时它运行正确，但有时会出错。

我认为，这会产生错误，因为我试图在活动中加载片段，然后当片段加载到活动中时，我试图打开不同的活动。但我无法修复。

菜单：

https://i.stack.imgur.com/V5auA.jpg

---

主要活动的相关部分：

public class MainActivity extends AppCompatActivity implements GoogleApiClient.ConnectionCallbacks,
GoogleApiClient.OnConnectionFailedListener, LocationListener {
private Context context;
private SharedPreference sharedPreference;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
context = MainActivity.this;
sharedPreference = SharedPreference.getInstance(context);
if (getIntent().hasExtra(Constants.SCREEN_TAG)) {
String type = getIntent().getStringExtra(Constants.SCREEN_TAG);
}
FloatingActionButton fabMainActivity = findViewById(R.id.fabMainActivity);
BottomNavigationView bnvMainActivity = findViewById(R.id.bnvMainActivity);
bnvMainActivity.setOnNavigationItemSelectedListener(onNavigationItemSelectedListener);
loadFragment(new DiscoverFragment());
fabMainActivity.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, PostJobActivity.class));
}
});
}
private BottomNavigationView.OnNavigationItemSelectedListener onNavigationItemSelectedListener = new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
Fragment selectedFragment = null;
switch (menuItem.getItemId()){
case R.id.navigation_discover:
selectedFragment = new DiscoverFragment();
break;
case R.id.navigation_nearby:
selectedFragment = new NearbyFragment();
break;
case R.id.empty_menu:
break;
case R.id.navigation_notification:
selectedFragment = new NotificationFragment();
break;
case R.id.navigation_profile:
selectedFragment = new ProfileFragment();
break;
}
loadFragment(selectedFragment);
return true;
}
};
private void loadFragment(Fragment fragment) {
FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.flMainActivity, fragment);
fragmentTransaction.commit();
}
}

---

主活动XML:

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout 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="match_parent"
tools:context=".Activity.MainActivity"
android:background="@color/app_background">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<RelativeLayout
android:id="@+id/rlTopBackgroundMainActivity"
android:layout_width="match_parent"
android:layout_height="75dp"
android:background="@drawable/top_background"
android:layout_gravity="top">
<ImageView
android:id="@+id/ivLogoWithTextMainActivity"
android:layout_width="142dp"
android:layout_height="41dp"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_alignParentBottom="true"
android:layout_marginStart="20dp"
android:layout_marginLeft="20dp"
android:layout_marginTop="23dp"
android:layout_marginEnd="247dp"
android:layout_marginRight="247dp"
android:layout_marginBottom="17dp"
android:layout_centerVertical="true"
android:contentDescription="@string/terms_activity_logo_with_text"
android:src="@drawable/logo_with_text" />
<ImageView
android:id="@+id/ivMessagesMainActivity"
android:layout_width="33dp"
android:layout_height="41dp"
android:src="@drawable/message_icon"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_centerVertical="true"
android:layout_marginRight="20dp"
android:layout_marginEnd="20dp"
android:contentDescription="@string/messages_icon" />
</RelativeLayout>
<FrameLayout
android:id="@+id/flMainActivity"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@+id/rlTopBackgroundMainActivity" />
</RelativeLayout>
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/bnvMainActivity"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@android:color/transparent"
android:layout_gravity="bottom"
app:itemIconTint="@color/bottom_menu_color"
app:menu="@menu/bottom_navigation_menu"
app:labelVisibilityMode="unlabeled" />
<com.google.android.material.bottomappbar.BottomAppBar
android:id="@+id/bapMainActivity"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/white"
app:itemIconTint="@color/bottom_menu_color"
app:labelVisibilityMode="unlabeled"
app:fabAlignmentMode="center"
app:fabCradleMargin="7dp"
app:elevation="0dp"
android:layout_gravity="bottom"/>
<com.google.android.material.floatingactionbutton.FloatingActionButton
android:id="@+id/fabMainActivity"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:backgroundTint="@color/purple_2"
app:tint="@android:color/white"
android:src="@drawable/post_job_icon"
app:layout_anchor="@id/bapMainActivity"
app:maxImageSize="35dp" />
</androidx.coordinatorlayout.widget.CoordinatorLayout>

---

作业后活动的相对部分：(作业后活动也在框架布局中。(

public class PostJobActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_post_job);
this.getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_ALWAYS_HIDDEN);
context = PostJobActivity.this;

btnBackToMainActivityPostJobActivity.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(PostJobActivity.this, MainActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
finish();
}
});
}

@Override
public void onBackPressed() {
Intent intent = new Intent(PostJobActivity.this, MainActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_CLEAR_TASK);
startActivity(intent);
finish();
}

}

---

错误消息：

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
at androidx.fragment.app.FragmentTransaction.doAddOp(FragmentTransaction.java:161)
at androidx.fragment.app.BackStackRecord.doAddOp(BackStackRecord.java:179)
at androidx.fragment.app.FragmentTransaction.replace(FragmentTransaction.java:225)
at androidx.fragment.app.FragmentTransaction.replace(FragmentTransaction.java:200)
at dk.lejekspert.lejekspertrekrutter.Activity.MainActivity.loadFragment(MainActivity.java:133)
at dk.lejekspert.lejekspertrekrutter.Activity.MainActivity.access$000(MainActivity.java:58)
at dk.lejekspert.lejekspertrekrutter.Activity.MainActivity$3.onNavigationItemSelected(MainActivity.java:126)
at com.google.android.material.bottomnavigation.BottomNavigationView$1.onMenuItemSelected(BottomNavigationView.java:243)
at androidx.appcompat.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:840)
at androidx.appcompat.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:158)
at androidx.appcompat.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:991)
at com.google.android.material.bottomnavigation.BottomNavigationMenuView$1.onClick(BottomNavigationMenuView.java:124)
at android.view.View.performClick(View.java:5723)
at android.view.View$PerformClick.run(View.java:22689)
at android.os.Handler.handleCallback(Handler.java:836)
at android.os.Handler.dispatchMessage(Handler.java:103)
at android.os.Looper.loop(Looper.java:203)
at android.app.ActivityThread.main(ActivityThread.java:6364)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924)

---

有解决这个问题的想法吗？谢谢

---

编辑：我在bottom_navigation_menu.xml文件中添加了一句话，使fab按钮下的菜单项不启用。

<item
android:id="@+id/empty_menu"
app:showAsAction="always"
android:enabled="false"
android:title="@string/nearby" />

此外，此代码部分不再是必需的。

case R.id.empty_menu:
break;

Answer 1

当使用fragment=null调用fragmentTransaction.replace(R.id.flMainActivity, fragment);时，会发生此问题。

检查onNavigationItemSelected。

public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
Fragment selectedFragment = null;
switch (menuItem.getItemId()){
//...
case R.id.empty_menu:
break;   //  <-- this case
}
loadFragment(selectedFragment);
return true;

在这种情况下，selectedFragment是null
检查问题中的屏幕，您似乎在BottomNavigationView中使用了一个菜单项，该菜单项没有FAB后面的图标。