Activity invokes the fragments of controls and change its properties,
Main activity layout is as follows:

 & lt; ? The XML version="1.0" encoding="utf-8"?> 
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="MainActivity" & gt; 

Android: layout_width="match_parent" 
Android: layout_height="match_parent" 
Android: orientation="vertical" 
The android: id="@ + id/layout_root & gt;" 

<frameLayout 
Android: layout_width="match_parent" 
Android: layout_height="match_parent" 
The android: id="@ + id/frame_layout" 
Android: layout_weight="1"/& gt; 

Android: layout_width="match_parent" 
Android: layout_height="wrap_content" 
The android: id="@ + id/button_change" 
Android: text="change"/& gt; 

 

 

MainActivity. Java is as follows:

 import androidx. Appcompat. App. AppCompatActivity; 
The import androidx. Fragments. App. Fragments; 
The import androidx. Fragments. App. FragmentManager; 
The import androidx. Fragments. App. FragmentTransaction; 


The import android. OS. Bundle; 
The import android. View. The view; 
The import android. Widget. The Button; 
The import android. Widget. TextView; 

Public class MainActivity extends AppCompatActivity {
Private fragments fragments; 
Private Button buttonChange; 

Private void initFragment (Bundle savedInstanceState) {
If (savedInstanceState==null) {
Fragments=new DemoFragment (); 
FragmentManager FragmentManager=getSupportFragmentManager (); 
FragmentTransaction FragmentTransaction=fragmentManager. BeginTransaction (); 
FragmentTransaction. Replace (R.i d.f rame_layout, fragments); 
//fragmentTransaction. The add (). The commit (); 
FragmentTransaction.com MIT (); 
} 
} 

Private TextView getFragmentTextView () {
TextView TextView=null; 
GetSupportFragmentManager (.) executePendingTransactions (); 
TextView=getSupportFragmentManager (.) findFragmentByTag (" DemoFragment "). The getView (). The findViewById (R.i which ext_view); 
GetSupportFragmentManager (.) executePendingTransactions (); 
Return the textView; 
} 

@ Override 
Protected void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_main); 

InitFragment (savedInstanceState); 

ButtonChange=(Button) the findViewById (R.i db utton_change); 

ButtonChange. SetOnClickListener (new View. An OnClickListener () {
@ Override 
Public void onClick (View v) {
GetFragmentTextView (). The setText (" Content End. "); 
} 
}); 

} 

} 

Debris layout is as follows:

 & lt; ? The XML version="1.0" encoding="utf-8"?> 
Android: orientation="vertical" 
Android: layout_width="match_parent" 
Android: layout_height="match_parent" & gt; 

Android: layout_width="match_parent" 
Android: layout_height="wrap_content" 
The android: id="@ + id/text_view" 
Android: text="Test Start." 
Android: gravity="center"/& gt; 

 

DemoFragment. Java is as follows:

 import android. OS. Bundle; 

The import androidx. Fragments. App. Fragments; 

The import android. View. LayoutInflater; 
The import android. View. The view; 
The import android. View. ViewGroup; 
The import android. Widget. TextView; 

/* * 
* A simple {@ link fragments} ttf_subclass. 
*/
Public class DemoFragment extends fragments {
Private TextView TextView; 

Public DemoFragment () {
//Required empty public constructor 
} 

@ Override 
Public View onCreateView (LayoutInflater inflater, ViewGroup container, 
Bundle savedInstanceState) {
The View demoView=inflater. Inflate (R.l ayout. Fragment_demo, container, false); 
DemoFragment demoView. SetTag (" "); 

TextView=(textView demoView). The findViewById (R.i which ext_view); 

Return demoView; 
} 

} 

Click on the button after an error is as follows:
E/AndroidRuntime: FATAL EXCEPTION: the main
Process: com. Sg. Fragmentsupportdemo1, PID: 4575
Java. Lang. NullPointerException: Attempt to invoke virtual method 'android. View. The view androidx. Fragments. The app. The fragments. The getView ()' on a null object reference
At com. Sg. Fragmentsupportdemo1. MainActivity. GetFragmentTextView (MainActivity. Java: 32)
At com. Sg. Fragmentsupportdemo1. MainActivity. Access the $000 (MainActivity. Java: 14)
At com. Sg. Fragmentsupportdemo1. MainActivity $1. The onClick (49) MainActivity. Java:

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