我正在尝试使用this教程实现自定义导航抽屉，但是当应用尝试启动时，我在NullPointerException上获得mDrawerList.setAdapter(adapter);。
代码如下;
MainActivity.java
public class MainActivity extends Activity {
TextView ConnectionStatus;
// For Navigation Drawer. From "http://www.androidhive.info/2013/11/android-sliding-menu-using-navigation-drawer/"
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;
// nav drawer title
private CharSequence mDrawerTitle;
// used to store app title
private CharSequence mTitle;
// slide menu items
private String[] navMenuTitles;
private TypedArray navMenuIcons;
private ArrayList<NavDrawerItem> navDrawerItems;
private NavDrawerListAdapter adapter;
// ***
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.home);
// For checking connection status
this.registerReceiver(this.mConnReceiver,
new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION));
ConnectionStatus = (TextView)findViewById(R.id.txtViewConnectionStatus);
// ***
// Setting up the Navigation Drawer
mTitle = mDrawerTitle = getTitle();
// load slide menu items
navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);
// nav drawer icons from resources
navMenuIcons = getResources().obtainTypedArray(R.array.nav_drawer_icons);
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerList = (ListView) findViewById(R.id.list_slidermenu);
navDrawerItems = new ArrayList<NavDrawerItem>();
// adding nav drawer items to array
// Home
navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));
// Find People
navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
// Photos
navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));
// Communities, Will add a counter here
navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons.getResourceId(3, -1), true, "22"));
// Pages
navDrawerItems.add(new NavDrawerItem(navMenuTitles[4], navMenuIcons.getResourceId(4, -1)));
// What's hot, We will add a counter here
navDrawerItems.add(new NavDrawerItem(navMenuTitles[5], navMenuIcons.getResourceId(5, -1), true, "50+"));
// Communities, Will add a counter here
navDrawerItems.add(new NavDrawerItem(navMenuTitles[6], navMenuIcons.getResourceId(6, -1), true, "22"));
// Pages
navDrawerItems.add(new NavDrawerItem(navMenuTitles[7], navMenuIcons.getResourceId(7, -1)));
// What's hot, We will add a counter here
navDrawerItems.add(new NavDrawerItem(navMenuTitles[8], navMenuIcons.getResourceId(8, -1), true, "50+"));
// Recycle the typed array
navMenuIcons.recycle();
// setting the nav drawer list adapter
adapter = new NavDrawerListAdapter(getApplicationContext(), navDrawerItems);
mDrawerList.setAdapter(adapter);
// enabling action bar app icon and behaving it as toggle button
getActionBar().setDisplayHomeAsUpEnabled(true);
getActionBar().setHomeButtonEnabled(true);
mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
R.drawable.ic_drawer, //nav menu toggle icon
R.string.app_name, // nav drawer open - description for accessibility
R.string.app_name // nav drawer close - description for accessibility
){
public void onDrawerClosed(View view) {
getActionBar().setTitle(mTitle);
// calling onPrepareOptionsMenu() to show action bar icons
invalidateOptionsMenu();
}
public void onDrawerOpened(View drawerView) {
getActionBar().setTitle(mDrawerTitle);
// calling onPrepareOptionsMenu() to hide action bar icons
invalidateOptionsMenu();
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
if (savedInstanceState == null) {
// on first time display view for first nav item
//displayView(0);
}
}
}
NavDrawerListAdapter.java
public class NavDrawerListAdapter extends BaseAdapter {
private Context context;
private ArrayList<NavDrawerItem> navDrawerItems;
public NavDrawerListAdapter(Context context, ArrayList<NavDrawerItem> navDrawerItems){
this.context = context;
this.navDrawerItems = navDrawerItems;
}
@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 (convertView == null) {
LayoutInflater mInflater = (LayoutInflater)
context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
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 txtCount = (TextView) convertView.findViewById(R.id.counter);
imgIcon.setImageResource(navDrawerItems.get(position).getIcon());
txtTitle.setText(navDrawerItems.get(position).getTitle());
// displaying count
// check whether it set visible or not
if(navDrawerItems.get(position).getCounterVisibility()){
txtCount.setText(navDrawerItems.get(position).getCount());
}else{
// hide the counter view
txtCount.setVisibility(View.GONE);
}
return convertView;
}
}
和 NavDrawerItem.java
public class NavDrawerItem {
private String title;
private int icon;
private String count = "0";
// boolean to set visiblity of the counter
private boolean isCounterVisible = false;
public NavDrawerItem(){}
public NavDrawerItem(String title, int icon){
this.title = title;
this.icon = icon;
}
public NavDrawerItem(String title, int icon, boolean isCounterVisible, String count){
this.title = title;
this.icon = icon;
this.isCounterVisible = isCounterVisible;
this.count = count;
}
public String getTitle(){
return this.title;
}
public int getIcon(){
return this.icon;
}
public String getCount(){
return this.count;
}
public boolean getCounterVisibility(){
return this.isCounterVisible;
}
public void setTitle(String title){
this.title = title;
}
public void setIcon(int icon){
this.icon = icon;
}
public void setCount(String count){
this.count = count;
}
public void setCounterVisibility(boolean isCounterVisible){
this.isCounterVisible = isCounterVisible;
}
}
drawer_list_item.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="48dp"
android:background="@drawable/list_selector">
<ImageView
android:id="@+id/icon"
android:layout_width="25dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_marginLeft="12dp"
android:layout_marginRight="12dp"
android:contentDescription="@string/desc_list_item_icon"
android:src="@drawable/ic_home"
android:layout_centerVertical="true" />
<TextView
android:id="@+id/title"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_toRightOf="@id/icon"
android:minHeight="?android:attr/listPreferredItemHeightSmall"
android:textAppearance="?android:attr/textAppearanceListItemSmall"
android:textColor="@color/list_item_title"
android:gravity="center_vertical"
android:paddingRight="40dp"/>
<TextView android:id="@+id/counter"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@drawable/counter_bg"
android:layout_alignParentRight="true"
android:layout_centerVertical="true"
android:layout_marginRight="8dp"
android:textColor="@color/counter_text_color"/>
</RelativeLayout>
答案 0 :(得分：0)
从您的布局文件中，您似乎正在尝试获取不存在的ListView的引用：
mDrawerList = (ListView) findViewById(R.id.list_slidermenu);
这就是你后来获得NPE的原因。如果您按照该教程进行操作，请检查布局文件（home.xml）中是否确实有类似教程中的定义：
<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<!-- Framelayout to display Fragments -->
<FrameLayout
android:id="@+id/frame_container"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<!-- Listview to display slider menu -->
<!-- This is the listView you are trying to find in your code. -->
<ListView
android:id="@+id/list_slidermenu"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:choiceMode="singleChoice"
android:divider="@color/list_divider"
android:dividerHeight="1dp"
android:listSelector="@drawable/list_selector"
android:background="@color/list_background"/>
</android.support.v4.widget.DrawerLayout>