Question

我已经在片段中创建了一个自定义按钮，并且尝试单击“活动”中的“导航抽屉” 。

当您滑过鼠标时，导航抽屉仍会打开，但是当我单击按钮时，应用程序就会崩溃。

我猜这是因为我正在尝试从Fragment访问，但是我很茫然。

片段

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>

崩溃日志

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

在您的实现中，您不这样做，因为drawer_layout无法访问fragment。因此，您得到了NullPointerException。尝试执行以下步骤：

步骤-1：在您的Activity中创建一个功能以打开关闭导航抽屉

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

步骤-2：从片段中调用openCloseNavigationDrawer

选项-1：从片段代码中删除OnClickListener，并通过布局添加onClick属性，并在openCloseNavigationDrawer上指出函数siteDrawerMenuButton 。

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

选项-2：您可以像下面那样强制转换openCloseNavigationDrawer，通过代码访问函数Activity：

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

Answer 2

聚会有点晚了，但如果有人觉得这很有用 - 它是 Jetpack Binding 的一行：

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 ) }

    }
}

LoginViewModel 是名为 Login 的片段的视图模型，R_id_nav_register 是 mobile_navigation.xml 和 activity_main_drawer.xml 中的一个元素

从片段中单击按钮打开导航抽屉（Kotlin）

2 个答案: