我知道这个问题已经出现了 100 次，但我所看到的都没有解决这个问题。我在一个名为 fragment_main 的布局中有一个按钮，它显示给另一个布局:activity_main。该按钮会打开一个名为 AddEditFragment 的 fragment ，它允许用户将信息添加到表单，然后将其吐到 MainActivity 中显示的 recyclerview(fragment_main) 中。
我有两种布局，因为在 activity_main 的线性布局中有一个抽屉导航，在 fragment_main 约束布局中有 recyclerview 和按钮。但是，我已经在 MainActivity 中启动并运行了 onDelete/Edit/Save 方法，因此将按钮 onClickListener 也放在那里对我来说才有意义。除了按钮不在主布局 activity_main 中，我得到一个致命的空对象异常。
即使 fragment_main 显示在 activity_main 中，是否有解决此问题的方法，以便可以将 OnClick 方法放入链接布局中按钮的 MainActivity 中？
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
我已经很接近了，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 个无法解决的错误。第一个在 view.findViewById 按钮初始化和回调方法中的 fragment_container 中显示。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
更简单的方法是把
onClick="AddEditRequestView"
在你的 fragment_main.xml 中
就是这样
<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" />
在你的 MainActivity.java 中
添加这个方法
public void AddEditRequestView(View viewc){
AddEditRequest(null);
}
并从您的 Activity 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/