getSupportFragmentManager().findFragmentById returning Null

问题

What I am doing: updating UI (Fragment UI) from Broadcast Receiver. But while finding Fragment I am getting null in return.

OnReceive (Broadcast Receiver):

 if(MainActivity.getInstace()!=null){
                MainActivity.getInstace().updateUI();
            }

MainActivity.class (Fragment Activity):

     public void updateUI() {
            MainActivity.this.runOnUiThread(new Runnable() {
                public void run() {

//getting null here 
                    SlidingTab frag = (SlidingTab)getSupportFragmentManager().findFragmentByTag("slidingtab");
                    frag.updateUI();
                }
            });
        } 

Code for calling Fragment from Activity:

 FragmentManager fragmentManager = getSupportFragmentManager();
                FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
                fragmentManager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);


                ft.setCustomAnimations(R.anim.glide_fragment_horizontal_in, R.anim.glide_fragment_horizontal_out);
                ft.replace(R.id.content_frame1, new SlidingTab(), "slidingtab");
                ft.addToBackStack("slidingtab");
                // Start the animated transition.
                ft.commit();
                break;

SlidingTab.class (Fragment UI update code ):

public class SlidingTab extends Fragment {
 public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.sliding_tab, container, false);}
    public void updateUI(){

                badge.setVisibility(View.VISIBLE);
    }
            }

Fragment (SlidingTab.xml)

<LinearLayout 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/frame_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/white"
    android:orientation="vertical"
    tools:context="com.RareMediaCompany.BDTrial.SlidingTab">

    <include
        android:id="@+id/toolbar1"
        layout="@layout/toolbar_job" />

    <com.RareMediaCompany.BDTrial.Utils.CustomTabLayout
        android:id="@+id/sliding_tabs"
        style="@style/CustomTabLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="#eeeeee"
        app:tabIndicatorColor="#f39220"
        app:tabIndicatorHeight="3dp"
        app:tabMaxWidth="0dp"
        app:tabMode="fixed"
        app:tabPaddingEnd="0dp"
        app:tabPaddingStart="0dp"
        app:tabTextAppearance="@android:style/TextAppearance.Widget.TabWidget"
        app:tabSelectedTextColor="#808080" />

    <LinearLayout
        android:id="@+id/linear1"
        android:background="@android:color/white"
        android:layout_width="match_parent"
        android:layout_height="70dp"
        android:layout_marginRight="8dp"
        android:layout_marginLeft="5dp"
        android:orientation="horizontal"
        android:weightSum="1">

        <android.support.v7.widget.SearchView
        android:layout_width="300dp"
        android:layout_height="45dp"
        android:id="@+id/searchView"
        android:layout_weight="1"
        android:layout_gravity="center"
            android:layout_marginEnd="5dp"
            android:clickable="true"
        style="@style/CitySearchView"
        android:background="@drawable/searchview"
        android:layout_marginLeft="5dp"/>

        <LinearLayout
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_vertical"
            android:weightSum="1"
            android:orientation="horizontal">

        <LinearLayout
            android:id="@+id/list_linearlayout"
            android:layout_width="45dp"
            android:layout_height="45dp"
            android:layout_weight="0.5"
            android:layout_gravity="center"
            android:background="#f39220">
        <!--android:background="#75aadb">-->
            <ImageView
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="2dp"
                android:layout_weight="0.3"
                android:src="@drawable/listicon"/>

        </LinearLayout>

        <LinearLayout
            android:id="@+id/maplist"
            android:layout_width="45dp"
            android:layout_height="45dp"
            android:layout_gravity="center"
            android:layout_weight="0.5"
            android:background="#75aadb">
            <ImageView
                android:layout_width="20dp"
                android:layout_height="wrap_content"
                android:layout_marginTop="2dp"
                android:layout_marginRight="3dp"
                android:layout_weight="0.3"
                android:src="@drawable/map_icon_1"/>

        </LinearLayout>
        </LinearLayout>

    </LinearLayout>
        <!--android:layout_width="320dp"-->
        <!--android:layout_height="wrap_content"-->
        <!--android:layout_marginLeft="10dp"-->
        <!--android:layout_marginTop="10dp"-->
        <!--android:id="@+id/searchview"/>-->

    <android.support.v4.view.ViewPager
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:background="@android:color/white" />

</LinearLayout>

The fragment (SlidingTab) consist of textviews and viewpager . And i am not able to find it in MainActivity.class. Every time i call
SlidingTab frag = (SlidingTab)getSupportFragmentManager().findFragmentByTag("slidingtab") Frag comes null.

回答1:

Use getSupportFragmentManager().executePendingTransactions() after fragment transaction. After calling this method you can get the fragment using both findFragmentById() and findFragmentByTag() methods.

Also make sure you pass Valid Id or Tag for the fragment.

来源：https://stackoverflow.com/questions/37806667/getsupportfragmentmanager-findfragmentbyid-returning-null