NavDrawerListAdapter中的NullPointerException for Android中的NavigationDrawer

Question

我有一个很奇怪的问题。 我在Android App中为NavigationDrawer使用了NavDrawerListAdapter。 如果列表中有13个项目（NavDrawerItem），则工作正常。 但是，当我添加第14个元素时，该应用程序似乎崩溃并给出了NullPointerException。 我检查了资源，字符串等，一切似乎都是正确的。 stacktrace指向以下行中的getView（）中的此类：

imgIcon.setImageResource（navDrawerItems.get（position）.getIcon（））;

由于某些原因，imgIcon为空。

public class NavDrawerListAdapter extends BaseAdapter {
    private static final String TAG = "NavDrawerListAdapter";
    private Context context;
    private ArrayList<NavDrawerItem> navDrawerItems;
    private List<Boolean> enabledDrawerItems;
    private LayoutInflater mInflater;

    public NavDrawerListAdapter(Context context,
            ArrayList<NavDrawerItem> navDrawerItems) 
    {
        super();
        this.context = context;
        this.navDrawerItems = navDrawerItems;
        this.mInflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);

        // Toggle enabled/disabled navigation drawer items
        enabledDrawerItems = new ArrayList<Boolean>(Arrays.asList(new Boolean[navDrawerItems.size()]));
        Collections.fill(enabledDrawerItems, new Boolean(true));
    }

    @Override
    public int getCount() {
        return navDrawerItems.size();
    }

    @Override
    public Object getItem(int position) {
        return navDrawerItems.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent)   {
        if(position == 0)       {
            convertView = mInflater.inflate(R.layout.header_view, null);
            return convertView;
        }

        if(convertView == null)     {
            // Use the drawer list item view
            convertView = mInflater.inflate(R.layout.drawer_list_item, null);
        }

        ImageView imgIcon = (ImageView) convertView.findViewById(R.id.icon);
        TextView txtTitle = (TextView) convertView.findViewById(R.id.title);
        TextView txtCounter = (TextView) convertView.findViewById(R.id.counter);

        Log.d(TAG, "Position: " + position + ", Icon Resource: " + navDrawerItems.get(position).getIcon());
        Log.d(TAG, "NavDrawerItems: " + navDrawerItems.size());
        if(imgIcon == null){
            Log.d(TAG, "imgIcon is null");
        }
        else{
            Log.d(TAG, "imgIcon is not null");
        }

        imgIcon.setImageResource(navDrawerItems.get(position).getIcon());
        txtTitle.setText(navDrawerItems.get(position).getTitle());

        if(navDrawerItems.get(position).isCounterVisible()){
            txtCounter.setText(navDrawerItems.get(position).getCount());
        }
        else{
            txtCounter.setVisibility(View.GONE);
        }

        if(enabledDrawerItems.get(position) == false)       {
            txtTitle.setTextColor(Color.LTGRAY);
            convertView.setEnabled(enabledDrawerItems.get(position));
        }
        return convertView;
    }

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

    @Override
    public boolean isEnabled(int position)  {
        return enabledDrawerItems.get(position);
    }

    // Set state of navigation drawer item
    public void setNavigationDrawerItem(int pos, boolean enabled)   {
        enabledDrawerItems.set(pos, enabled);
    }
}

strings.xml

<array name="nav_drawer_icons">
        <item>@drawable/ic_home</item>
        <item>@drawable/ic_people</item>
        <item>@drawable/ic_photos</item>
        <item>@drawable/ic_communities</item>
        <item>@drawable/ic_pages</item>
        <item>@drawable/ic_whats_hot</item>
    </array>

NavigationDrawerActivity

public class NavigationDrawerActivity extends ActionBarActivity {
    public DrawerLayout mDrawerLayout;
    public ListView mDrawerList;
    private ActionBarDrawerToggle mDrawerToggle;

    public CharSequence mDrawerTitle; // nav drawer title
    public CharSequence mTitle; // store app title

    public TypedArray navMenuIcons; // menu item icons
    public String[] navMenuTitles; // menu item titles

    public ArrayList<NavDrawerItem> navDrawerItems; // each drawer item
    public NavDrawerListAdapter adapter; // nav drawer adapter

    // Static Settings/Configuration
    private static final int NAVIGATION_DRAWER_WIDTH_PERCENT = 85; // in percentage
    private static final String TAG = "MainActivity";
    public static final String INTENT_EXTRA_POSITION = "NavigationDrawerPosition";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Use ToolBar and set it as ActionBar
        Toolbar toolbar = (Toolbar) findViewById(R.id.my_awesome_toolbar);

        setSupportActionBar(toolbar);

        // Get Nav Menu Icons and Titles
        navMenuIcons = getResources().obtainTypedArray(R.array.nav_drawer_icons);
        navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);

        // Get DrawerLayout and ListView
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerList = (ListView) findViewById(R.id.list_slidermenu);

        navDrawerItems = new ArrayList<NavDrawerItem>();

        addNavDrawerItems(); // add each navigation drawer item

        // Recycle the array
        navMenuIcons.recycle();

        // setup the nav drawer list adapter
        adapter = new NavDrawerListAdapter(this.getApplicationContext(), navDrawerItems);

        mDrawerList.setAdapter(adapter);
        mDrawerList.setOnItemClickListener(new SlideMenuClickListener());

        // enabling action bar app icon and behaving it as toggle button
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setHomeButtonEnabled(true);

        mDrawerToggle = new ActionBarDrawerToggle(this,
                                                  mDrawerLayout,
//                                                R.drawable.ic_drawer,
                                                  R.string.app_name,
                                                  R.string.app_name)
        {
            public void onDrawerClosed(View view){
                getSupportActionBar().setTitle(mTitle);
                invalidateOptionsMenu();
            }

            public void onDrawerOpened(View drawerView){
                getSupportActionBar().setTitle(mTitle);
                invalidateOptionsMenu();
            }
        };

        mDrawerLayout.setDrawerListener(mDrawerToggle);

        Intent intent = getIntent();
        if(intent != null && intent.getExtras() != null) {
            int drawerPosition = intent.getExtras().getInt(INTENT_EXTRA_POSITION);
            if(drawerPosition != 0) {
                // update selected item, title, and close drawer
                mDrawerList.setItemChecked(drawerPosition, true);
                mDrawerList.setSelection(drawerPosition);
                setTitle(navMenuTitles[drawerPosition-1]);
            }
            else {
                Log.w(TAG, "drawerPosition is 0");
            }
        }

        mDrawerTitle = getTitle();
        mTitle = mDrawerTitle;

        configureNavigationDrawer();
        configureEnabledDisabledNavDrawItems();
    }

    private void configureEnabledDisabledNavDrawItems() {
        // Check if Device is connected (No: disable list item, Yes: enable list item)
        if(SecondScreenIAB.getInstance().getDevice() == null)
        {
            getAdapter().setNavigationDrawerItem(2, false); 
            getAdapter().setNavigationDrawerItem(3, false); 
        }
        else
        {
            getAdapter().setNavigationDrawerItem(2, true); 
            getAdapter().setNavigationDrawerItem(3, true); 
        }
    }

    private void addNavDrawerItems() {
        navDrawerItems.add(new NavDrawerItem(0, "")); // Drawer Cover Image
        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(0, -1), navMenuTitles[0]));             
        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(1, -1), navMenuTitles[1]));             
        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(2, -1), navMenuTitles[2]));             

        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(3, -1), navMenuTitles[3]));             
        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(4, -1), navMenuTitles[4], "23", false));
        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(5, -1), navMenuTitles[5]));             
        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(0, -1), navMenuTitles[6], "5", false)); 

        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(1, -1), navMenuTitles[7]));             

        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(2, -1), navMenuTitles[8]));             
        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(3, -1), navMenuTitles[9]));             
        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(4, -1), navMenuTitles[10]));            
        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(5, -1), navMenuTitles[11]));            
        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(0, -1), navMenuTitles[12]));            

        navDrawerItems.add(new NavDrawerItem(navMenuIcons.getResourceId(1, -1), navMenuTitles[13]));            
    }

    public void configureActionBar()    {
        SpannableString s = new SpannableString("Test");
        s.setSpan(new TypefaceSpan(this, "Roboto-Regular.ttf"), 0, s.length(),
                Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);

        // Update the action bar title with the TypefaceSpan instance
        android.support.v7.app.ActionBar actionBar = this.getSupportActionBar();
        actionBar.setTitle(s);
    }

    private void configureNavigationDrawer()    {
        // Configure Navigation Drawer Width
        DrawerLayout.LayoutParams params = (android.support.v4.widget.DrawerLayout.LayoutParams) mDrawerList.getLayoutParams();
        params.width = (int) (getResources().getDisplayMetrics().widthPixels * (NAVIGATION_DRAWER_WIDTH_PERCENT/100.0));
        mDrawerList.setLayoutParams(params);
    }

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if(mDrawerToggle.onOptionsItemSelected(item)){
            return true;
        }

        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu){
        boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
        menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
        return super.onPrepareOptionsMenu(menu);
    }

    @Override
    public void setTitle(CharSequence title) {
        mTitle = title;
        getSupportActionBar().setTitle(mTitle);
    }

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        mDrawerToggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        mDrawerToggle.onConfigurationChanged(newConfig);
    }
    public ListView getmDrawerList() {
        return mDrawerList;
    }

    public void setmDrawerList(ListView mDrawerList) {
        this.mDrawerList = mDrawerList;
    }

    public NavDrawerListAdapter getAdapter() {
        return adapter;
    }

    public void setAdapter(NavDrawerListAdapter adapter) {
        this.adapter = adapter;
    }
}

Answer 1

您似乎正在使用两种不同的布局：

• R.layout.header_view
• R.layout.drawer_list_item

我猜“ R.layout.header_view”没有“ R.id.icon”。 因此，当它尝试重用它时，imgIcon为null。

基本适配器具有方法

public int getItemViewType (int position)
public int getViewTypeCount ()

您有两种类型的视图。 您需要确保位置0的项目与其他项目的类型不同。

您需要将这两种方法添加到适配器中：

@Override
public int getItemViewType (int position) {
    if(position == 0)
        return 0;
    else
        return 1;
}

@Override
public int getViewTypeCount () {
    return 2;
}

然后将getView中的第一个if语句更新为：

    if(position == 0) {
        if(convertView == null)
             convertView = mInflater.inflate(R.layout.header_view, null);
        return convertView;
    }

Answer 2

从baseAdapter中删除标头，请在主java中执行以下操作，让您的baseAdapter添加标头

View header = getLayoutInflater().inflate(R.layout.header_view, null); 

ListView listView = getListView();  
listView.addHeaderView(header); 
listView.setAdapter(myAdapter);