android - 在抽屉导航 Activity 布局上启用和禁用 MenuItem

Question

我已经使用 Navigation Drawer Activity 布局创建了应用程序。我需要以编程方式启用/禁用一些项目

Menu Example

示例:我想禁用菜单项 id nav_item2

我试着做...

MenuItem nav_item2 = (MenuItem)findViewById(R.id.nav_item2);
nav_item2.setEnabled(false);

然后它返回一个NullPointerException给我..

也尝试过...

@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    super.onPrepareOptionsMenu(menu);
    nav_item2 = menu.findItem(R.id.nav_item2);
    return true;
}

具有相同的NullPointerException

有人知道该做什么吗？

nav_header_main_activity.xml(与布局创建一起生成)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="@dimen/nav_header_height"
    android:background="@drawable/side_nav_bar"
    android:gravity="bottom"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:theme="@style/ThemeOverlay.AppCompat.Dark">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="199dp"
        android:layout_height="72dp"
        android:paddingTop="@dimen/nav_header_vertical_spacing"
        android:src="@drawable/ciag" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingTop="@dimen/nav_header_vertical_spacing"
        android:text="CIAg"
        android:textAppearance="@style/TextAppearance.AppCompat.Body1" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="dev@ciag.org.br" />

</LinearLayout>

main_activity_navigation_drawer.xml(在布局创建时生成)

<group android:checkableBehavior="single">
    <item
        android:id="@+id/nav_save"
        android:icon="@android:drawable/ic_menu_save"
        android:enabled="false"
        android:title="@string/nav_save" />
    <item
        android:id="@+id/nav_graph"
        android:icon="@drawable/chart_bar"
        android:enabled="false"
        android:title="@string/nav_graph" />
    <item
        android:id="@+id/nav_send"
        android:icon="@drawable/ic_menu_send"
        android:title="Enviar" />
</group>

<item android:title="Configurações">
    <menu>
        <item
            android:id="@+id/nav_manage"
            android:icon="@drawable/ic_menu_manage"
            android:enabled="false"
            android:title="@string/nav_manage" />
        <item
            android:id="@+id/nav_support"
            android:icon="@android:drawable/ic_menu_help"
            android:title="@string/nav_support" />
    </menu>
</item>

Answer 1

您可以从 NavigationView.getMenu() 访问菜单

Below is code :

NavigationView navigationView= findViewById(R.id.nav_id_in_layout)

Menu menuNav=navigationView.getMenu();
MenuItem nav_item2 = menuNav.findItem(R.id.nav_item2);
nav_item2.setEnabled(false)