Why element is null in fragment in activity
<p>I have one Fragment and ImageView in fragment in Activity.</p>

<p>I want to show image on ImageView.</p>

<p>But ImageView is null in Fragment.</p>

<p>Why? I Don't know.</p>

<p>Fragment Code : </p>

<pre><code>@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.fragment_blank, container, false);

    imageView1 =(ImageView)view.findViewById(R.id.imageView1);

    new WallPaperSync().execute();

    return  view;
}
</code></pre>

<p>Fragment Layout Code :</p>

<pre><code>&lt;FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.burak.apps.BlankFragment"&gt;

&lt;!-- TODO: Update blank fragment layout --&gt;


&lt;ImageButton
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/imageView1"/&gt; &lt;/FrameLayout&gt;
</code></pre>

<p>Main Activity :</p>

<pre><code>public class MainActivity extends AppCompatActivity
    implements NavigationView.OnNavigationItemSelectedListener,BlankFragment.OnFragmentInteractionListener{

public TextView twUserName;
private static String image;
private ImageButton imageView;
private Button btnGetir;
private static final int CONTENT_VIEW_ID = 10101010;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
            this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
    drawer.setDrawerListener(toggle);
    toggle.syncState();

    NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
    navigationView.setNavigationItemSelectedListener(this);


    View header = LayoutInflater.from(this).inflate(R.layout.nav_header_main, null);
    navigationView.addHeaderView(header);
    twUserName = (TextView) header.findViewById(R.id.TwUserName);
    twUserName.setText(LoginEntites.UserName);




    final  View main = getLayoutInflater().from(this).inflate(R.layout.content_main, null);
 //   navigationView.addHeaderView(main);


    //        imageView = (ImageButton)main.findViewById(R.id.imageButton);
            //new WallPaperSync().execute();
    if (savedInstanceState == null) {
        BlankFragment f = new BlankFragment();
        FragmentManager fm = getFragmentManager();
        FragmentTransaction ft = fm.beginTransaction();

        ft.add(R.id.fragmentLayout,f);
        ft.commit();

    }


}

@Override
public void onBackPressed() {
    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    } else {
        super.onBackPressed();
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
    // Handle navigation view item clicks here.
    int id = item.getItemId();

    if (id == R.id.nav_camara) {
        // Handle the camera action
    } else if (id == R.id.nav_gallery) {

    } else if (id == R.id.nav_slideshow) {

    } else if (id == R.id.nav_manage) {

    } else if (id == R.id.nav_share) {

    } else if (id == R.id.nav_send) {

    }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);
    return true;
}

@Override
public void onFragmentInteraction(Uri uri) {

}
</code></pre>

<p>Content Activity Layout :</p>

<pre><code>&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:showIn="@layout/app_bar_main"
tools:context="com.example.burak.apps.MainActivity"&gt;
 &lt;RelativeLayout
    android:id="@+id/fragmentLayout"
    android:layout_width="150dp"
    android:layout_height="150dp"&gt;
&lt;/RelativeLayout&gt;
&lt;/RelativeLayout&gt;
</code></pre>

<p>Thanks for all help.</p>