从 Fragment 中的按钮单击打开导航抽屉 (Kotlin)

Question

I have created a custom button in a Fragment and I am trying to open the Navigation Drawer in the Activity when it is clicked.

The Navigation Drawer still opens ok when you swipe across, but the app just crashes when I click the button.

I guess this is because I am trying to access from the Fragment, but I am at a loss..

Fragment

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?): View? {
    // Inflate the layout for this fragment
    val binding: SiteFragmentBinding = DataBindingUtil.inflate(
        inflater, R.layout.site_fragment, container, false
    )

    binding.apply {
        siteOverflowOptionsMenuButton.setOnClickListener{
            showPopUp(it)
        }

        siteDrawerMenuButton.setOnClickListener{
            drawer_layout.openDrawer(nav_view)  // this crashes (also crashes with Gravity.LEFT or similar)
        }

    }

    return binding.root
}

activity.xml

?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:fitsSystemWindows="true"
    tools:openDrawer="start">

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

        <androidx.fragment.app.FragmentContainerView
            android:id="@+id/siteNavHostFragment"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:defaultNavHost="true"
            app:navGraph="@navigation/site_navigation" />

    </LinearLayout>

    <com.google.android.material.navigation.NavigationView
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:id="@+id/nav_view"
        app:headerLayout="@layout/nav_header"
        app:menu="@menu/drawer_menu"

        />

</androidx.drawerlayout.widget.DrawerLayout>

site_fragment.xml

 <?xml version="1.0" encoding="utf-8"?> <layout 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"> <data> </data> <androidx.constraintlayout.widget.ConstraintLayout android:id="@+id/siteMainConstraintLayout" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@color/white" tools:context=".site.SiteActivity" > <androidx.constraintlayout.widget.ConstraintLayout android:id="@+id/siteLogoConstraintLayout" android:layout_width="wrap_content" android:layout_height="50dp" android:layout_marginTop="16dp" android:foregroundGravity="center_horizontal" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent"> <ImageView android:id="@+id/siteLogoImage" android:layout_width="50dp" android:layout_height="match_parent" android:src="@mipmap/ic_launcher_logo" app:layout_constraintEnd_toStartOf="@id/siteTopHeadingText" app:layout_constraintHorizontal_chainStyle="packed" app:layout_constraintStart_toStartOf="parent" /> <TextView android:id="@+id/siteTopHeadingText" android:layout_width="wrap_content" android:layout_height="match_parent" android:gravity="center_vertical" android:paddingStart="12dp" android:paddingLeft="12dp" android:text="@string/site_top_heading" android:textAppearance="@style/TextAppearance.AppCompat.Medium" android:textSize="18sp" android:textStyle="bold|italic" app:layout_constraintEnd_toEndOf="parent" /> </androidx.constraintlayout.widget.ConstraintLayout> <ImageView android:id="@+id/siteOverflowOptionsMenuButton" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginEnd="16dp" android:layout_marginRight="16dp" app:srcCompat="@drawable/ic_menu_vertical_dots" android:tint="@color/locatorsPurpleCompany" app:layout_constraintBottom_toBottomOf="@+id/siteLogoConstraintLayout" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintTop_toTopOf="@+id/siteLogoConstraintLayout" /> <ImageView android:id="@+id/siteDrawerMenuButton" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginStart="16dp" android:layout_marginLeft="16dp" app:srcCompat="@drawable/ic_menu_drawer" android:tint="@color/locatorsPurpleCompany" app:layout_constraintBottom_toBottomOf="@+id/siteLogoConstraintLayout" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="@+id/siteLogoConstraintLayout" /> <androidx.cardview.widget.CardView android:id="@+id/siteFilterOptionsCardView" android:layout_width="match_parent" android:layout_height="60dp" android:layout_marginStart="8dp" android:layout_marginTop="8dp" android:layout_marginEnd="8dp" android:layout_marginRight="8dp" app:cardBackgroundColor="@color/locatorsGrey" app:cardCornerRadius="18dp" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toBottomOf="@+id/siteLogoConstraintLayout"> <androidx.constraintlayout.widget.ConstraintLayout android:id="@+id/siteFilterOptionsConstraintLayout" android:layout_width="match_parent" android:layout_height="match_parent"> <ImageView android:id="@+id/siteFilterIconImageView" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginStart="8dp" android:layout_marginLeft="8dp" app:srcCompat="@drawable/ic_filter" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" /> <TextView android:id="@+id/siteCurrentFilterTextView" android:layout_width="0dp" android:layout_height="0dp" android:layout_marginStart="8dp" android:layout_marginLeft="8dp" android:layout_marginTop="4dp" android:layout_marginEnd="8dp" android:layout_marginRight="8dp" android:layout_marginBottom="4dp" android:background="@color/white" android:drawableLeft="@drawable/ic_search" android:drawablePadding="8dp" android:ellipsize="end" android:gravity="center_vertical" android:lines="1" android:paddingLeft="12dp" android:paddingRight="12dp" android:text="Search..." app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toStartOf="@+id/siteClearIconImageView" app:layout_constraintStart_toEndOf="@+id/siteFilterIconImageView" app:layout_constraintTop_toTopOf="parent" /> <ImageView android:id="@+id/siteClearIconImageView" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginEnd="8dp" android:layout_marginRight="8dp" app:srcCompat="@drawable/ic_clear" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintTop_toTopOf="parent" /> </androidx.constraintlayout.widget.ConstraintLayout> </androidx.cardview.widget.CardView> <androidx.recyclerview.widget.RecyclerView android:id="@+id/siteRecyclerView" android:layout_width="match_parent" android:layout_height="0dp" android:layout_marginBottom="4dp" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toBottomOf="@+id/siteFilterOptionsCardView" app:layout_constraintVertical_bias="0.0" tools:listitem="@layout/site_list_item" /> <com.google.android.material.floatingactionbutton.FloatingActionButton android:id="@+id/floatingActionButtonAdd" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginEnd="32dp" android:layout_marginRight="32dp" android:layout_marginBottom="24dp" android:backgroundTint="@color/locatorsPurpleCompany" android:clickable="true" android:elevation="28dp" app:borderWidth="0dp" app:fabSize="normal" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="@+id/siteRecyclerView" app:srcCompat="@drawable/ic_add_white" /> </androidx.constraintlayout.widget.ConstraintLayout> </layout>

drawer_menu.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    >

    <group android:checkableBehavior="single">
        <item
            android:id="@+id/nav_first_fragment"
            android:icon="@drawable/ic_exit"
            android:title="First" />
        <item
            android:id="@+id/nav_second_fragment"
            android:icon="@drawable/ic_priority"
            android:title="Second" />
        <item
            android:id="@+id/nav_third_fragment"
            android:icon="@drawable/ic_filter"
            android:title="Third" />
    </group>

    <item android:title="Communicate">
        <menu>
            <item
                android:id="@+id/nav_share"
                android:icon="@drawable/ic_contact"
                android:title="Share" />
            <item
                android:id="@+id/nav_send"
                android:icon="@drawable/ic_location"
                android:title="Send" />
        </menu>

    </item>

    <item android:title="Sub items">
        <menu>
            <group android:checkableBehavior="single">
                <item
                    android:icon="@drawable/ic_star_full"
                    android:title="Sub item 1" />
                <item
                    android:icon="@drawable/ic_location"
                    android:title="Sub item 2" />
            </group>
        </menu>
    </item>
</menu>

Crash Log

2020-02-17 12:31:56.719 23527-23527/com.locators.acorn E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.locators.acorn, PID: 23527
java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.drawerlayout.widget.DrawerLayout.openDrawer(int)' on a null object reference
    at com.locators.acorn.site.SiteFragment$onCreateView$$inlined$apply$lambda$2.onClick(SiteFragment.kt:46)
    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)

Answer 1

In your implementation, you don't do that as drawer_layout is not accessible from fragment . Hence you got NullPointerException . Try to follow below steps:

Step - 1: Create a function in your Activity to open-close Navigation Drawer

fun openCloseNavigationDrawer(view: View) {
    if (drawer_layout.isDrawerOpen(GravityCompat.START)) {
        drawer_layout.closeDrawer(GravityCompat.START)
    } else {
        drawer_layout.openDrawer(GravityCompat.START)
    }
}

Step - 2: Invoke openCloseNavigationDrawer from your fragment

• Option - 1: Remove OnClickListener from your fragment code and add onClick property through layout and pointed out the function openCloseNavigationDrawer on siteDrawerMenuButton .

    <ImageView
        android:id="@+id/siteDrawerMenuButton"
        android:onClick="openCloseNavigationDrawer"
        ... />

• Option - 2: You can access the function openCloseNavigationDrawer through code by casting your Activity like below:

    siteDrawerMenuButton.setOnClickListener{ v ->
        (activity as YOUR_ACTIVITY).openCloseNavigationDrawer(v)
    }

Answer 2

A bit late to the party, but in case someone finds this useful - it's a single line with Jetpack Binding:

class LoginViewModel ( applicationParam: Application ) : AndroidViewModel ( applicationParam )
{

    screenViews     = FragmentLoginBinding.inflate ( inflater,container,false )


    override fun onViewCreated ( view: View, savedInstanceState: Bundle? )
    {
        // Set click listener for the Log in button
        screenViews.login.setOnClickListener { submitLogin() }

        // Set the click listener for the element that selects the register fragment from the navigation drawer
        screenViews.goToRegisterFragment.setOnClickListener { findNavController().navigate ( R.id.nav_register ) }

    }
}

With LoginViewModel being the view model for a fragment called Login, and R_id_nav_register being an element in mobile_navigation.xml and activity_main_drawer.xml