我正在设计一个导航抽屉，其中包含列表中每个项目的图标。我完全按照this教程。但我得到了一个运行时例外。
这是我的logcat。
11-12 12:15:53.767 5237-5237/com.myayubo E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.myayubo, PID: 5237
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myayubo/com.myayubo.Extract}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2338)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:110)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:5299)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.myayubo.Extract.onCreate(Extract.java:60)
at android.app.Activity.performCreate(Activity.java:5264)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1088)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2302)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:110)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:5299)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
at dalvik.system.NativeStart.main(Native Method)
在这里，我只在列表中放了一个项目（只是为了检查）
这是我的strings.xml
<resources>
<string name="app_name">My Ayubo</string>
<string name="title_activity_maps">Map</string>
<string name="title_activity_login">LoginActivity</string>
<string name="hello_world">Hello world!</string>
<string name="action_settings">Settings</string>
<string name="title_activity_splash">Splash</string>
<string name="title_activity_extract_menu">ExtractMenu</string>
<string-array name="titles">
<item>hotel</item>
<item>resturant</item>
<item>wildlife</item>
</string-array>
<array name="icons">
<item>@drawable/ic_hotel</item>
<item>@drawable/ic_resturant</item>
<item>@drawable/ic_wildlife</item>
</array>
<string name="navigation_drawer_open">Open navigation drawer</string>
<string name="navigation_drawer_close">Close navigation drawer</string>
<string name="action_example">Example action</string>
<string name="title_activity_sign_up">sign_up</string>
<string name="app_id">914777611938198</string>
<string name="title_activity_extract">Extract</string>
</resources>
这是我的Extract.java（主要活动）
public class Extract extends ActionBarActivity {
String[] menutitles;
TypedArray menuIcons;
// nav drawer title
private CharSequence mDrawerTitle;
private CharSequence mTitle;
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;
private List<RowItem> rowItems;
private CustomAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_extract);
mTitle = mDrawerTitle = getTitle();
menutitles = getResources().getStringArray(R.array.titles);
menuIcons = getResources().obtainTypedArray(R.array.icons);
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerList = (ListView) findViewById(R.id.slider_list);
rowItems = new ArrayList<RowItem>();
for (int i = 0; i < menutitles.length; i++) {
RowItem items = new RowItem(menutitles[i], menuIcons.getResourceId( i, -1));
rowItems.add(items);
}
menuIcons.recycle();
adapter = new CustomAdapter(getApplicationContext(), rowItems);
mDrawerList.setAdapter(adapter);
mDrawerList.setOnItemClickListener(new SlideitemListener());
// 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, R.string.app_name,R.string.app_name)
{
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
updateDisplay(0);
}
}
class SlideitemListener implements ListView.OnItemClickListener {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
updateDisplay(position);
}
}
private void updateDisplay(int position) {
Fragment fragment = null;
switch (position) {
case 0:
fragment = new hotel();
break;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction().replace(R.id.frame_container, fragment).commit();
// update selected item and title, then close the drawer
setTitle(menutitles[position]);
mDrawerLayout.closeDrawer(mDrawerList);
}
else {
// error in creating fragment
Log.e("Extract", "Error in creating fragment");
}
}
@Override
public void setTitle(CharSequence title) {
mTitle = title;
getActionBar().setTitle(mTitle);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_extract, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// toggle nav drawer on selecting action bar app icon/title
if (mDrawerToggle.onOptionsItemSelected(item)) {
return true;
}
// Handle action bar actions click
switch (item.getItemId()) {
case R.id.action_settings:
return true;
default :
return super.onOptionsItemSelected(item);
}
}
/*** * Called when invalidateOptionsMenu() is triggered */
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
// if nav drawer is opened, hide the action items
boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
return super.onPrepareOptionsMenu(menu);
}
/** * When using the ActionBarDrawerToggle, you must call it during * onPostCreate() and onConfigurationChanged()... */
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
// Sync the toggle state after onRestoreInstanceState has occurred.
mDrawerToggle.syncState(); }
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
// Pass any configuration change to the drawer toggles
mDrawerToggle.onConfigurationChanged(newConfig);
}
}
这是我的activity_extract.xml
<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 -->
<ListView
android:id="@+id/slider_list"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:background="#ffffff"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp" />
</android.support.v4.widget.DrawerLayout>
这是我的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:padding="5dp" >
<ImageView
android:id="@+id/icon"
android:layout_width="50dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:layout_marginLeft="12dp"
android:layout_marginRight="12dp"
/>
<TextView
android:id="@+id/title"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_marginTop="10dp"
android:layout_toRightOf="@id/icon"
android:gravity="center_vertical"
android:textColor="#000000"
android:textSize="20sp" />
</RelativeLayout>
这是我的RowItem.java
package com.myayubo;
public class RowItem {
private String title;
private int icon;
public RowItem(String title, int icon) {
this.title = title;
this.icon = icon;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public int getIcon() {
return icon;
}
public void setIcon(int icon) {
this.icon = icon;
}
}
这是我的CustomAdapter.java
public class CustomAdapter extends BaseAdapter {
Context context; List<RowItem> rowItem;
CustomAdapter(Context context, List<RowItem> rowItem) {
this.context = context;
this.rowItem = rowItem;
}
@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.list_item, null);
}
ImageView imgIcon = (ImageView) convertView.findViewById(R.id.icon);
TextView txtTitle = (TextView) convertView.findViewById(R.id.title);
RowItem row_pos = rowItem.get(position);
// setting the image resource and title
imgIcon.setImageResource(row_pos.getIcon());
txtTitle.setText(row_pos.getTitle());
return convertView;
}
@Override
public int getCount() {
return rowItem.size();
}
@Override
public Object getItem(int position) {
return rowItem.get(position);
}
@Override
public long getItemId(int position) {
return rowItem.indexOf(getItem(position));
}
}
这是我的hotel.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="match_parent" >
<ImageView
android:id="@+id/imageView1"
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="148dp"
android:src="@drawable/ic_locationhotel" />
</RelativeLayout>
这是我的hotel.java
public class hotel extends Fragment {
@Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View rootView = inflater .inflate(R.layout.hotel, container, false);
return rootView;
}
}
我无法确定这里发生了什么。我之前没有真正实现过导航抽屉。这就是我遵循以下教程中的确切步骤的原因。我该怎么做才能完美地运行它？
- 编辑 -
Here is my `AndrdoidManifest.xml`
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.myayubo"
android:versionCode="1"
android:versionName="1.0" >
<supports-screens
android:anyDensity="true"
android:largeScreens="true"
android:normalScreens="true"
android:resizeable="true"
android:smallScreens="true"
android:xlargeScreens="true" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES" />
<!--
The ACCESS_COARSE/FINE_LOCATION permissions are not required to use
Google Maps Android API v2, but are recommended.
-->
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<!--
To retrieve OAuth 2.0 tokens or invalidate tokens to disconnect a user. This disconnect
option is required to comply with the Google+ Sign-In developer policies
-->
<uses-permission android:name="android.permission.USE_CREDENTIALS" /> <!-- To retrieve the account name (email) as part of sign-in: -->
<uses-permission android:name="android.permission.GET_ACCOUNTS" /> <!-- To auto-complete the email text field in the login form with the user's emails -->
<uses-permission android:name="android.permission.READ_PROFILE" />
<uses-permission android:name="android.permission.READ_CONTACTS" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<meta-data
android:name="com.google.android.gms.version"
android:value="@integer/google_play_services_version" />
<meta-data
android:name="com.google.android.maps.v2.API_KEY"
android:value="@string/google_maps_key" />
<meta-data
android:name="com.facebook.sdk.ApplicationId"
android:value="@string/app_id" />
<activity
android:name=".Splash"
android:label="Ayubo" >
<!-- Intent filter should be here -->
</activity>
<activity
android:name=".LoginActivity"
android:label="@string/title_activity_login"
android:windowSoftInputMode="adjustResize|stateHidden" >
</activity>
<activity
android:name=".sign_up"
android:label="@string/title_activity_sign_up" >
</activity>
<activity
android:name=".MapsActivity"
android:label="@string/title_activity_maps" >
</activity>
<activity
android:name="com.facebook.LoginActivity" />
<activity
android:name=".Extract"
android:label="@string/title_activity_extract"
android:theme="@style/Theme.AppCompat.Light" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
-Edit 2（新错误） -
11-12 13:31:44.753 11673-11673/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.myayubo, PID: 11673
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myayubo/com.myayubo.Extract}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2338)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:110)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:5299)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.myayubo.Extract.onCreate(Extract.java:60)
at android.app.Activity.performCreate(Activity.java:5264)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1088)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2302)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2390)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1321)
at android.os.Handler.dispatchMessage(Handler.java:110)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:5299)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：1)
您正在使用ActionBarActivity，这是带有操作栏的活动的app compat版本。
在清单中的android:theme=”@style/Theme.AppCompat.Light”标记中为<activity>活动添加以下属性Extract。
app compat库的目的是为旧版本的API提供功能。问题是Android改变了他们的Android SDK以包含ActionBar，但只有Honeycomb及以上版本。 App compat ActionBarActivity旨在为更低版本的API添加Action栏功能。但是，为了激活＆＃34;存在操作栏，您需要为您的活动指定特定的应用程序compat主题。
PS：此外，作为免责声明，您总体上使用了一种旧的Action栏概念。现在Android开发人员正在谈论工具栏，需要以不同的方式添加。 Android developers介绍了如何在详细信息中添加工具栏。请记住，如果你去工具栏，你需要更改我要求你添加的主题，因为你会得到重复的操作栏。
答案 1 :(得分：0)
使用 getSupportActionBar() instead of getActionBar() 解决了问题。现在按预期工作。