我正在制作一款Android应用，我决定添加一个联系人列表。
我跟随this lesson from Google并且我已复制代码并将所有功能添加到我的应用程序中，位于目录：xml/layout/images/javacode etc中，并在我的主要活动中调用联系人列表活动。如果我在手机上通过Android Studio上的调试运行KitKat 4.4.2，我的应用程序可以工作。但是，如果我运行Lollipop 5.1.1，则在尝试访问联系人活动时应用程序会崩溃。
似乎有问题的代码：
if (Utils.hasHoneycomb()) {
// Enables action bar "up" navigation
getActionBar().setDisplayHomeAsUpEnabled(true);
}
logcat的：
02-18 13:41:15.304 31435-31435/todonotes.com.todonotes_buildfinale E/AndroidRuntime: FATAL EXCEPTION: main
Process: todonotes.com.todonotes_buildfinale, PID: 31435
java.lang.RuntimeException: Unable to start activity ComponentInfo{todonotes.com.todonotes_buildfinale/todonotes.com.todonotes_buildfinale.ContactDetailActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2378)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2440)
at android.app.ActivityThread.access$800(ActivityThread.java:162)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1348)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5422)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:914)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:707)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
at todonotes.com.todonotes_buildfinale.ContactDetailActivity.onCreate(ContactDetailActivity.java:59)
at android.app.Activity.performCreate(Activity.java:6057)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2331)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2440)
at android.app.ActivityThread.access$800(ActivityThread.java:162)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1348)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5422)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:914)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:707)
我的文件：
<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="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_CONTACTS"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/Theme.AppCompat.NoActionBar">
<activity android:name="todonotes.com.todonotes_buildfinale.SplashScreen"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name="todonotes.com.todonotes_buildfinale.LoginActivity" android:theme="@style/AppTheme.Dark"
android:label="@string/app_name">
<intent-filter>
<action android:name="todonotes.com.todonotes_buildfinale.SIGNUPACTIVITY"/>
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
<activity
android:name="todonotes.com.todonotes_buildfinale.ContactsListActivity" android:theme="@style/AppTheme"
android:label="@string/activity_contacts_list"
android:windowSoftInputMode="adjustResize">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
<!-- Add intent-filter for search intent action and specify searchable configuration
via meta-data tag. This allows this activity to receive search intents via the
system hooks. In this sample this is only used on older OS versions (pre-Honeycomb)
via the activity search dialog. See the Search API guide for more information:
http://developer.android.com/guide/topics/search/search-dialog.html -->
<intent-filter>
<action android:name="android.intent.action.SEARCH" />
</intent-filter>
<meta-data android:name="android.app.searchable"
android:resource="@xml/searchable_contacts" />
</activity>
<activity
android:name="todonotes.com.todonotes_buildfinale.ContactDetailActivity" android:theme="@style/AppTheme"
android:label="@string/activity_contact_detail"
android:parentActivityName="todonotes.com.todonotes_buildfinale.ContactDetailActivity">
<!-- Define hierarchical parent of this activity, both via the system
parentActivityName attribute (added in API Level 16) and via meta-data annotation.
This allows use of the support library NavUtils class in a way that works over
all Android versions. See the "Tasks and Back Stack" guide for more information:
http://developer.android.com/guide/components/tasks-and-back-stack.html
-->
<meta-data android:name="android.support.PARENT_ACTIVITY"
android:value="todonotes.com.todonotes_buildfinale.ContactDetailActivity" />
</activity>
<activity android:name="todonotes.com.todonotes_buildfinale.SignupActivity" android:theme="@style/AppTheme.Dark"></activity>
<activity android:name="todonotes.com.todonotes_buildfinale.ConfirmActivity" android:theme="@style/AppTheme.Dark"></activity>
<activity android:name="todonotes.com.todonotes_buildfinale.ListNoteActivity" android:theme="@style/AppTheme.Dark"></activity>
</application>
</manifest>
活动：
public class ContactDetailActivity extends FragmentActivity {
// Defines a tag for identifying the single fragment that this activity holds
private static final String TAG = "ContactDetailActivity";
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
@Override
protected void onCreate(Bundle savedInstanceState) {
//setContentView(R.layout.contact_detail_fragment);
if (BuildConfig.DEBUG) {
// Enable strict mode checks when in debug modes
Utils.enableStrictMode();
}
super.onCreate(savedInstanceState);
// This activity expects to receive an intent that contains the uri of a contact
if (getIntent() != null) {
// For OS versions honeycomb and higher use action bar
if (Utils.hasHoneycomb()) {
// Enables action bar "up" navigation
//getActionBar().setDisplayHomeAsUpEnabled(true);
//((ActionBarActivity))getActivity()).getSupportActionBar();
if(getActionBar()!=null){
getActionBar().setDisplayHomeAsUpEnabled(true);
}
//getActionBar().setDisplayHomeAsUpEnabled(true);
}
// Fetch the data Uri from the intent provided to this activity
final Uri uri = getIntent().getData();
// Checks to see if fragment has already been added, otherwise adds a new
// ContactDetailFragment with the Uri provided in the intent
if (getSupportFragmentManager().findFragmentByTag(TAG) == null) {
final FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
// Adds a newly created ContactDetailFragment that is instantiated with the
// data Uri
ft.add(android.R.id.content, ContactDetailFragment.newInstance(uri), TAG);
ft.commit();
}
} else {
// No intent provided, nothing to do so finish()
finish();
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// Tapping on top left ActionBar icon navigates "up" to hierarchical parent screen.
// The parent is defined in the AndroidManifest entry for this activity via the
// parentActivityName attribute (and via meta-data tag for OS versions before API
// Level 16). See the "Tasks and Back Stack" guide for more information:
// http://developer.android.com/guide/components/tasks-and-back-stack.html
NavUtils.navigateUpFromSameTask(this);
return true;
}
// Otherwise, pass the item to the super implementation for handling, as described in the
// documentation.
return super.onOptionsItemSelected(item);
}
}
我该如何解决这个问题？
更新：
在contactDetails中我修改了以下代码：
public class ContactDetailActivity extends AppCompatActivity {
if (Utils.hasHoneycomb()) {
if(getSupportActionBar()!=null){
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}
//getActionBar().setDisplayHomeAsUpEnabled(true);
}
结果是： the bar in the list is missing
问题在于此活动：CONTACTLISTACTIVITY
public class ContactsListActivity extends FragmentActivity implements
ContactsListFragment.OnContactsInteractionListener {
// Defines a tag for identifying log entries
private static final String TAG = "ContactsListActivity";
private ContactDetailFragment mContactDetailFragment;
// If true, this is a larger screen device which fits two panes
private boolean isTwoPaneLayout;
// True if this activity instance is a search result view (used on pre-HC devices that load
// search results in a separate instance of the activity rather than loading results in-line
// as the query is typed.
private boolean isSearchResultView = false;
@Override
protected void onCreate(Bundle savedInstanceState) {
if (BuildConfig.DEBUG) {
Utils.enableStrictMode();
}
super.onCreate(savedInstanceState);
// Set main content view. On smaller screen devices this is a single pane view with one
// fragment. One larger screen devices this is a two pane view with two fragments.
setContentView(R.layout.activity_main);
// Check if two pane bool is set based on resource directories
isTwoPaneLayout = getResources().getBoolean(R.bool.has_two_panes);
// Check if this activity instance has been triggered as a result of a search query. This
// will only happen on pre-HC OS versions as from HC onward search is carried out using
// an ActionBar SearchView which carries out the search in-line without loading a new
// Activity.
if (Intent.ACTION_SEARCH.equals(getIntent().getAction())) {
// Fetch query from intent and notify the fragment that it should display search
// results instead of all contacts.
String searchQuery = getIntent().getStringExtra(SearchManager.QUERY);
ContactsListFragment mContactsListFragment = (ContactsListFragment)
getSupportFragmentManager().findFragmentById(R.id.contact_list);
// This flag notes that the Activity is doing a search, and so the result will be
// search results rather than all contacts. This prevents the Activity and Fragment
// from trying to a search on search results.
isSearchResultView = true;
mContactsListFragment.setSearchQuery(searchQuery);
// Set special title for search results
String title = getString(R.string.contacts_list_search_results_title, searchQuery);
setTitle(title);
}
if (isTwoPaneLayout) {
// If two pane layout, locate the contact detail fragment
mContactDetailFragment = (ContactDetailFragment)
getSupportFragmentManager().findFragmentById(R.id.contact_detail);
}
}
/**
* This interface callback lets the main contacts list fragment notify
* this activity that a contact has been selected.
*
* @param contactUri The contact Uri to the selected contact.
*/
@Override
public void onContactSelected(Uri contactUri) {
if (isTwoPaneLayout && mContactDetailFragment != null) {
// If two pane layout then update the detail fragment to show the selected contact
mContactDetailFragment.setContact(contactUri);
} else {
// Otherwise single pane layout, start a new ContactDetailActivity with
// the contact Uri
Intent intent = new Intent(this, ContactDetailActivity.class);
intent.setData(contactUri);
startActivity(intent);
}
}
/**
* This interface callback lets the main contacts list fragment notify
* this activity that a contact is no longer selected.
*/
@Override
public void onSelectionCleared() {
if (isTwoPaneLayout && mContactDetailFragment != null) {
mContactDetailFragment.setContact(null);
}
}
@Override
public boolean onSearchRequested() {
// Don't allow another search if this activity instance is already showing
// search results. Only used pre-HC.
return !isSearchResultView && super.onSearchRequested();
}
}
最后修改：
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<item name="colorPrimary">@color/primary</item>
<item name="colorPrimaryDark">@color/primary_dark</item>
<item name="colorAccent">@color/accent</item>
</style>
我已经在我的样式xml中执行此操作....在清单中我的活动使用AppTheme然后我更改了myActivity扩展AppCompatActivity。
答案 0 :(得分：0)
为避免异常，请使用：
if(getActionBar()!=null){
getActionBar().setDisplayHomeAsUpEnabled(true);
}
但最好的方法是让您的活动延长AppCompatActivity。
然后使用：
if(getSupportActionBar()!=null){
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}