Итак, я пытаюсь вызвать некоторые методы расширенного класса фрагмента в mainActivity и каким-то образом я не могу получить переменную для ссылки на фактический фрагмент.
Он говорит, что я ссылаюсь на нулевой объект, когда я вызываю фрагмент. метод () строка. Это из-за неправильного идентификатора в findFragmentByid () внутри onCreate () в mainActivity?
Я пытался использовать идентификатор линейного макета и макета ограничения ('yes' и 'paint'), все еще получаю ошибку .
Основная деятельность
public class MainActivity extends AppCompatActivity {
public ViewGroup.LayoutParams params;
private Path path=new Path();
private Paint brush = new Paint();
private PaintView paintView;
FirstFragment frag=new FirstFragment();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
frag = (FirstFragment) getSupportFragmentManager().findFragmentById(R.id.paint);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar2);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayShowTitleEnabled(false);
toolbar.setMinimumWidth(20);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.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
switch (id){
case R.id.eraser:
frag.eraser();
return true;
case R.id.brush:
frag.brush();
return true;
}
return super.onOptionsItemSelected(item);
}
}
Первый фрагмент
public class FirstFragment extends Fragment {
public FirstFragment() {}
private PaintView paintView;
@Override
public View onCreateView(
LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState
) {
View rootView=inflater.inflate(R.layout.fragment_first,container,false);
LinearLayout Rl= (LinearLayout) rootView.findViewById(R.id.paint);
paintView=new PaintView(getActivity());
Rl.addView(paintView);
// Inflate the layout for this fragment
return rootView;
}
public void onViewCreated(@NonNull View view, Bundle savedInstanceState) {
paintView.brush();
super.onViewCreated(view, savedInstanceState);
/*
view.findViewById(R.id.button_first).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
NavHostFragment.findNavController(FirstFragment.this)
.navigate(R.id.action_FirstFragment_to_SecondFragment);
}
});
*/
}
public void eraser()
{
paintView.eraser();
}
public void brush(){
paintView.brush();
}
}
first_fragment. 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"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/yes"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".FirstFragment" >
<LinearLayout
android:id="@+id/paint"
android:layout_width="409dp"
android:layout_height="0dp"
android:layout_marginStart="1dp"
android:layout_marginTop="1dp"
android:layout_marginEnd="1dp"
android:orientation="horizontal"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"></LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
Ошибка
Process: com.example.myapplication, PID: 29743
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.myapplication.FirstFragment.eraser()' on a null object reference
at com.example.myapplication.MainActivity.onOptionsItemSelected(MainActivity.java:50)
at android.app.Activity.onMenuItemSelected(Activity.java:4137)
at androidx.fragment.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:436)
at androidx.appcompat.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:196)
at androidx.appcompat.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:109)
at androidx.appcompat.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:109)
at androidx.appcompat.app.ToolbarActionBar$2.onMenuItemClick(ToolbarActionBar.java:64)
at androidx.appcompat.widget.Toolbar$1.onMenuItemClick(Toolbar.java:204)
at androidx.appcompat.widget.ActionMenuView$MenuBuilderCallback.onMenuItemSelected(ActionMenuView.java:781)
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 androidx.appcompat.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:981)
at androidx.appcompat.widget.ActionMenuView.invokeItem(ActionMenuView.java:625)
at androidx.appcompat.view.menu.ActionMenuItemView.onClick(ActionMenuItemView.java:151)
at android.view.View.performClick(View.java:7125)
at android.view.View.performClickInternal(View.java:7102)
at android.view.View.access$3500(View.java:801)
at android.view.View$PerformClick.run(View.java:27336)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
29743-29743/com.example.myapplication I/Process: Sending signal. PID: 29743 SIG: 9