java - OnClickListener空对象引用

我知道这个问题已经被解决了100次，但是我没有看到解决这个问题的方法。我在名为fragment_main的布局中有一个按钮，该按钮显示为另一种布局：activity_main。该按钮将打开一个名为AddEditFragment的片段，该片段允许用户向表单中添加信息，然后将其吐到MainActivity中显示的recyclerview（fragment_main）中。

由于在activity_main的线性布局中有一个导航抽屉，在fragment_main约束的布局中有recyclerview和按钮，因此我有两种布局。但是我已经设置了onDelete / Edit / Save方法并进入MainActivity，所以对我来说也应该将按钮onClickListener放在这里才有意义。除了该按钮不在主布局activity_main中之外，我收到一个致命的空对象异常。

即使在activity_main中显示了fragment_main，还是可以解决此问题，以便可以将OnClick方法放入MainActivity中以链接布局中的按钮吗？

MainActivity.java

public class MainActivity extends AppCompatActivity implements RecyclerViewAdapter.OnVehicleClickListener,
                                                                FragmentAddEdit.OnSaveClicked,
                                                                NavigationView.OnNavigationItemSelectedListener {

    private DrawerLayout drawer;

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

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

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

        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar,
                R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        // Launcher view
        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                    new FragmentMainActivity()).commit();
            navigationView.setCheckedItem(R.id.nav_garage);
        }

        Button button_add = findViewById(R.id.button_add);


        button_add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                AddEditRequest(null);
            }
        });

    }


    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.nav_garage:
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                        new FragmentMainActivity()).commit();
                break;
            case R.id.nav_history:
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                        new FragmentHistory()).commit();
                break;
            case R.id.nav_upcoming:
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                        new FragmentUpcoming()).commit();
                break;
            case R.id.nav_about:
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                        new FragmentAbout()).commit();
                break;
        }

        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    @Override
    public void onSaveClicked() {

        FragmentManager fragmentManager = getSupportFragmentManager();
        Fragment AddEditFragment = fragmentManager.findFragmentById(R.id.fragment_container);
        if (AddEditFragment != null) {
            getSupportFragmentManager().beginTransaction()
                    .remove(AddEditFragment)
                    .commit();
        }

    }

    public void onEditClick(@NonNull Vehicle vehicle) {
        AddEditRequest(vehicle);
    }

    @Override
    public void onDeleteClick(@NonNull Vehicle vehicle) {

    }

    private void AddEditRequest(Vehicle vehicle) {

        Intent detailIntent = new Intent(this, FragmentAddEdit.class);
        if (vehicle != null) {
            detailIntent.putExtra(Vehicle.class.getSimpleName(), vehicle);
            startActivity(detailIntent);
        }


    }



    @Override
    public void onBackPressed() {
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout 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/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".com.carupkeep.MainActivity"
    tools:openDrawer="start">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/colorPrimary"
            android:elevation="4dp"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

        <FrameLayout
            android:id="@+id/fragment_container"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

    </LinearLayout>

    <android.support.design.widget.NavigationView
        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:headerLayout="@layout/nav_header"
        app:menu="@menu/drawer_menu" />

</android.support.v4.widget.DrawerLayout>

fragment_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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/content_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".com.carupkeep.FragmentMainActivity"
    tools:showIn="@layout/activity_main">

    <TextView
        android:id="@+id/no_vehicles"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/no_vehicle_message"
        android:textSize="22sp"
        android:textStyle="normal|bold"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:layout_constraintLeft_creator="1"
        tools:layout_constraintTop_creator="1"/>

    <Button
        android:id="@+id/button_add"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:drawableLeft="@drawable/ic_add"
        android:drawablePadding="10dp"
        android:drawableTint="@color/colorAdd"
        android:paddingLeft="30dp"
        android:paddingRight="30dp"
        android:text="@string/addVehicle"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/vehicle_list" />

    <android.support.v7.widget.RecyclerView
        android:id="@+id/vehicle_list"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginTop="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/no_vehicles"
        app:layout_constraintVertical_bias="0.0" />

</android.support.constraint.ConstraintLayout>

更新

我离得很近，但仍然感觉很远。我已经放弃尝试将其保留在MainActivity中，并按照建议将其放入FragmentMainAcitivity中。除了现在我有2无法解决错误。第一个在view.findViewById按钮初始化中的视图上，并且在回调方法的fragment_container上。关于如何解决这个问题有什么想法吗？

public class FragmentMainActivity extends Fragment {

    Button button_add = view.findViewById(R.id.button_add);

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_main, container, false);

        button_add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                FragmentManager fragmentManager = getFragmentManager();
                Fragment AddEditFragment = fragmentManager.findFragmentById(R.id.fragment_container);
getFragmentManager().beginTransaction().replace(fragment_container, AddEditFragment).commit();
            }
        });
    }
}

最佳答案

更简单的方法是将

onClick="AddEditRequestView"

在fragment_main.xml中

所以会的

<Button
        android:id="@+id/button_add"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:drawableLeft="@drawable/ic_add"
        android:drawablePadding="10dp"
        android:drawableTint="@color/colorAdd"
        android:paddingLeft="30dp"
        android:paddingRight="30dp"
        android:text="@string/addVehicle"
    android:onClick="AddEditRequestView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/vehicle_list" />

并在您的MainActivity.java中

添加此方法

public void AddEditRequestView(View viewc){
AddEditRequest(null);
}

并从您的活动中删除这些代码

 Button button_add = findViewById(R.id.button_add);


        button_add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                AddEditRequest(null);
            }
        });

关于java - OnClickListener空对象引用，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/51939010/