Question

救救我！ NavigationView无法创建列表视图。我想在NavigationView右侧创建列表菜单。

代码无错误无法运行错误

：java.lang.RuntimeException：无法启动活动 ComponentInfo {jp.vertice.myapplication / jp.vertice.myapplication.MainActivity}： java.lang.NullPointerException：尝试调用虚方法'void android.widget.ListView.setAdapter（android.widget.ListAdapter）'上的一个 null对象引用

MainActivity.java

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {
        ListView listView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        listView = (ListView) findViewById(R.id.listView);

        String[] values = new String[] { "List 1",
                "List 2",
                "List 3",
                "List 4",
                "List 5"
        };

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, android.R.id.text1, values);

        listView.setAdapter(adapter);

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {

                int itemPosition     = position;

                String  itemValue    = (String) listView.getItemAtPosition(position);

                Toast.makeText(getApplicationContext(),
                        "Position :" + itemPosition + "  ListItem : " + itemValue, Toast.LENGTH_LONG)
                        .show();
            }
        });
    }

activity_main.xml中

<?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:openDrawer="start">

    <include
        layout="@layout/app_bar_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <android.support.design.widget.NavigationView
        android:id="@+id/nav_view_right"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="end"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/nav_menu_right" />

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

nav_menu_right.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/listView" />
</LinearLayout>

Answer 1

我已更新您的代码，请替换为您的代码。 NullPointerException的原因是你试图直接找到listView但listView是NavigationView的Header，所以首先你需要找到NavigationView的视图，然后从NavigationView获取标题并使用该标题你可以找到你想要的listView。

public class MainActivity extends AppCompatActivity 
        implements NavigationView.OnNavigationItemSelectedListener { 
        ListView listView;
    @Override 
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        NavigationView navigationViewRight = (NavigationView) findViewById(R.id.nav_view_right);
        View header = navigationViewRight.getHeaderView(0);
        listView = (ListView) header.findViewById(R.id.listView);

        String[] values = new String[] { "List 1",
                "List 2", 
                "List 3", 
                "List 4", 
                "List 5" 
        }; 

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, android.R.id.text1, values);

        listView.setAdapter(adapter);

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override 
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {

                int itemPosition     = position;

                String  itemValue    = (String) listView.getItemAtPosition(position);

                Toast.makeText(getApplicationContext(),
                        "Position :" + itemPosition + "  ListItem : " + itemValue, Toast.LENGTH_LONG)
                        .show(); 
            } 
        }); 
    }

Answer 2

您可以使用自定义ListView创建它。请参阅下面的代码 activity_navigation_view.xml

<?xml version="1.0" encoding="utf-8"?>
    <android.support.v4.widget.DrawerLayout
        android:id="@+id/drawer_layout"
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true">

        <include layout="@layout/navigation_view_fragment_container"/>

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

            <ExpandableListView
                android:id="@+id/navigationmenu"
                android:layout_width="wrap_content"
                android:layout_height="match_parent"
                android:layout_marginTop="192dp"
                android:background="@android:color/white">
            </ExpandableListView>
        </android.support.design.widget.NavigationView>
    </android.support.v4.widget.DrawerLayout>

可扩展列表视图的适配器如下所示。

ExpandableListAdapter.java

public class ExpandableListAdapter extends BaseExpandableListAdapter {
    private Context mContext;
    private List<ExpandedMenuModel> mListDataHeader; // header titles

    // child data in format of header title, child title
    private HashMap<ExpandedMenuModel, List<String>> mListDataChild;
    ExpandableListView expandList;

    public ExpandableListAdapter(Context context, List<ExpandedMenuModel> listDataHeader, HashMap<ExpandedMenuModel, List<String>> listChildData, ExpandableListView mView) {
        this.mContext = context;
        this.mListDataHeader = listDataHeader;
        this.mListDataChild = listChildData;
        this.expandList = mView;
    }

    @Override
    public int getGroupCount() {
        int i = mListDataHeader.size();
        Log.d("GROUPCOUNT", String.valueOf(i));
        return this.mListDataHeader.size();
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        int childCount = 0;
        if (groupPosition != 2) {
            childCount = this.mListDataChild.get(this.mListDataHeader.get(groupPosition))
                .size();
        }
        return childCount;
    }

    @Override
    public Object getGroup(int groupPosition) {
        return this.mListDataHeader.get(groupPosition);
    }

    @Override
    public Object getChild(int groupPosition, int childPosition) {
        Log.d("CHILD", mListDataChild.get(this.mListDataHeader.get(groupPosition))
            .get(childPosition).toString());
        return this.mListDataChild.get(this.mListDataHeader.get(groupPosition))
            .get(childPosition);
    }

    @Override
    public long getGroupId(int groupPosition) {
        return groupPosition;
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return childPosition;
    }

    @Override
    public boolean hasStableIds() {
        return false;
    }

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
        ExpandedMenuModel headerTitle = (ExpandedMenuModel) getGroup(groupPosition);
        if (convertView == null) {
            LayoutInflater infalInflater = (LayoutInflater) this.mContext
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = infalInflater.inflate(R.layout.listheader, null);
        }
        TextView lblListHeader = (TextView) convertView
            .findViewById(R.id.submenu);
        ImageView headerIcon = (ImageView) convertView.findViewById(R.id.iconimage);
        lblListHeader.setTypeface(null, Typeface.BOLD);
        lblListHeader.setText(headerTitle.getIconName());
        headerIcon.setImageResource(headerTitle.getIconImg());
        return convertView;
    }

    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
        final String childText = (String) getChild(groupPosition, childPosition);

        if (convertView == null) {
            LayoutInflater infalInflater = (LayoutInflater) this.mContext
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = infalInflater.inflate(R.layout.list_submenu, null);
        }

        TextView txtListChild = (TextView) convertView
            .findViewById(R.id.submenu);

        txtListChild.setText(childText);

        return convertView;
    }

    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) {
        return true;
    }
}

list_submenu.xml如下。

    <?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="match_parent"
              android:orientation="vertical">

    <TextView
        android:id="@+id/submenu"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="20dp"
        android:padding="10dp"
        android:textColor="#000000"
        android:textSize="18sp"/>
</LinearLayout>

listheader.xml如下。

<?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="2dp"
              android:orientation="vertical">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginLeft="20dp"
        android:orientation="horizontal">

        <ImageView
            android:id="@+id/iconimage"
            android:layout_width="50dp"
            android:layout_height="50dp"
            android:paddingBottom="10dp"
            android:paddingLeft="10dp"
            android:paddingTop="10dp"/>

        <TextView
            android:id="@+id/submenu"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="10dp"
            android:textColor="#000000"
            android:textSize="20sp"/>

    </LinearLayout>

</LinearLayout>

在导航视图活动中，为可扩展列表视图设置适配器。 NavigationViewActivity.java

public class NavigationViewActivity extends AppCompatActivity {

    private DrawerLayout mDrawerLayout;
    ExpandableListAdapter mMenuAdapter;
    ExpandableListView expandableList;
    List<ExpandedMenuModel> listDataHeader;
    HashMap<ExpandedMenuModel, List<String>> listDataChild;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_navigation_view);
        final ActionBar ab = getSupportActionBar();
        /* to set the menu icon image*/
        ab.setHomeAsUpIndicator(R.drawable.ic_menu);
        ab.setDisplayHomeAsUpEnabled(true);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        expandableList = (ExpandableListView) findViewById(R.id.navigationmenu);
        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);

        if (navigationView != null) {
            setupDrawerContent(navigationView);
        }

        prepareListData();
        mMenuAdapter = new ExpandableListAdapter(this, listDataHeader, listDataChild, expandableList);

        // setting list adapter
        expandableList.setAdapter(mMenuAdapter);
    }

    private void prepareListData() {
        listDataHeader = new ArrayList<ExpandedMenuModel>();
        listDataChild = new HashMap<ExpandedMenuModel, List<String>>();

        ExpandedMenuModel item1 = new ExpandedMenuModel();
        item1.setIconName("heading1");
        item1.setIconImg(R.drawable.ic_menu_grid_view1);
        // Adding data header
        listDataHeader.add(item1);

        ExpandedMenuModel item2 = new ExpandedMenuModel();
        item2.setIconName("heading2");
        item2.setIconImg(R.drawable.ic_menu_list_view);
        listDataHeader.add(item2);

        ExpandedMenuModel item3 = new ExpandedMenuModel();
        item3.setIconName("heading3");
        item3.setIconImg(R.drawable.ic_attachment_album);
        listDataHeader.add(item3);

        // Adding child data
        List<String> heading1 = new ArrayList<String>();
        heading1.add("Submenu of item 1");

        List<String> heading2 = new ArrayList<String>();
        heading2.add("Submenu of item 2");
        heading2.add("Submenu of item 2");
        heading2.add("Submenu of item 2");

        listDataChild.put(listDataHeader.get(0), heading1);// Header, Child data
        listDataChild.put(listDataHeader.get(1), heading2);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case android.R.id.home:
                mDrawerLayout.openDrawer(GravityCompat.START);
                return true;
        }
        return super.onOptionsItemSelected(item);
    }

    private void setupDrawerContent(NavigationView navigationView) {
        navigationView.setNavigationItemSelectedListener(
            new NavigationView.OnNavigationItemSelectedListener() {
                @Override
                public boolean onNavigationItemSelected(MenuItem menuItem) {
                    menuItem.setChecked(true);
                    mDrawerLayout.closeDrawers();
                    return true;
                }
            });
    }

    }
    ExpandedMenuModel class contains menu item details as follow.

    ExpandedMenuModel.java

    public class ExpandedMenuModel {

    String iconName = "";
    int iconImg = -1; // menu icon resource id

    public String getIconName() {
        return iconName;
    }
    public void setIconName(String iconName) {
        this.iconName = iconName;
    }
    public int getIconImg() {
        return iconImg;
    }
    public void setIconImg(int iconImg) {
        this.iconImg = iconImg;
    } 
    }

Android Studio NavigationView无法创建listview

2 个答案: