具有多个活动的导航抽屉。 - 空指针异常
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【中文标题】具有多个活动的导航抽屉。 - 空指针异常【英文标题】：Navigation Drawer with Multiple activities. - NullPointerException 【发布时间】：2015-03-04 01:48:48 【问题描述】：我正在通过 android Studio 开发我的移动应用程序。我的应用程序的启动器活动是SplashScreen。带有Intent 的SplashScreen 导航到我的HomeActivity。我尝试了this博客中的代码，这样我就可以有一个导航抽屉，但在活动之间而不是片段之间。
在Splashscreen 和HomeActivity 活动中，我不想拥有这个抽屉。在HomeActivity 中有一个按钮（signin）。当您按下它时，您通常会导航到 SearchActivity，这是我想要拥有导航抽屉的第一页。
在上面的示例中，启动器活动是BaseActivity。因为我不希望BaseActivity 成为我的启动器活动，正如我所描述的，我在单击HomeActivity 内的signin 按钮后导航到BaseActivity。
我的 HomeActivity.java：
import android.content.Intent;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.ViewAnimator;
import common.activities.SampleActivityBase;
import common.logger.Log;
import common.logger.LogFragment;
import common.logger.LogWrapper;
import common.logger.MessageOnlyLogFilter;
public class HomeActivity extends SampleActivityBase
public static final String TAG = "HomeActivity";
// Whether the Log Fragment is currently shown
private boolean mLogShown;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final ImageButton send = (ImageButton)findViewById(R.id.signin);
send.setOnClickListener(new View.OnClickListener()
public void onClick(View view)
Intent intent = new Intent(HomeActivity.this, BaseActivity.class);
startActivity(intent);
finish();
);
if (savedInstanceState == null)
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
SlidingTabsColorsFragment fragment = new SlidingTabsColorsFragment();
transaction.replace(R.id.sample_content_fragment, fragment);
transaction.commit();
@Override
public boolean onCreateOptionsMenu(Menu menu)
getMenuInflater().inflate(R.menu.main, menu);
return true;
@Override
public boolean onPrepareOptionsMenu(Menu menu)
MenuItem logToggle = menu.findItem(R.id.menu_toggle_log);
logToggle.setVisible(findViewById(R.id.sample_output) instanceof ViewAnimator);
logToggle.setTitle(mLogShown ? "hide" : "show");
return super.onPrepareOptionsMenu(menu);
@Override
public boolean onOptionsItemSelected(MenuItem item)
// switch(item.getItemId())
// case R.id.menu_toggle_log:
// mLogShown = !mLogShown;
// ViewAnimator output = (ViewAnimator) findViewById(R.id.sample_output);
// if (mLogShown)
// //output.setDisplayedChild(1);
// else
// //output.setDisplayedChild(0);
//
// supportInvalidateOptionsMenu();
// return true;
//
return super.onOptionsItemSelected(item);
/** Create a chain of targets that will receive log data */
@Override
public void initializeLogging()
// Wraps Android's native log framework.
LogWrapper logWrapper = new LogWrapper();
// Using Log, front-end to the logging chain, emulates android.util.log method signatures.
Log.setLogNode(logWrapper);
// Filter strips out everything except the message text.
MessageOnlyLogFilter msgFilter = new MessageOnlyLogFilter();
logWrapper.setNext(msgFilter);
// On screen logging via a fragment with a TextView.
// LogFragment logFragment = (LogFragment) getSupportFragmentManager()
// .findFragmentById(R.id.log_fragment);
// msgFilter.setNext(logFragment.getLogView());
//
// Log.i(TAG, "Ready");
我的基本活动：
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.widget.DrawerLayout;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.FrameLayout;
import android.widget.ListView;
import android.widget.Toast;
/**
* @author dipenp
*
* This activity will add Navigation Drawer for our application and all the code related to navigation drawer.
* We are going to extend all our other activites from this BaseActivity so that every activity will have Navigation Drawer in it.
* This activity layout contain one frame layout in which we will add our child activity layout.
*/
public class BaseActivity extends Activity
/**
* Frame layout: Which is going to be used as parent layout for child activity layout.
* This layout is protected so that child activity can access this
* */
protected FrameLayout frameLayout;
/**
* ListView to add navigation drawer item in it.
* We have made it protected to access it in child class. We will just use it in child class to make item selected according to activity opened.
*/
protected ListView mDrawerList;
/**
* List item array for navigation drawer items.
* */
protected String[] listArray = "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" ;
/**
* Static variable for selected item position. Which can be used in child activity to know which item is selected from the list.
* */
protected static int position;
/**
* This flag is used just to check that launcher activity is called first time
* so that we can open appropriate Activity on launch and make list item position selected accordingly.
* */
private static boolean isLaunch = true;
/**
* Base layout node of this Activity.
* */
private DrawerLayout mDrawerLayout;
/**
* Drawer listner class for drawer open, close etc.
*/
private ActionBarDrawerToggle actionBarDrawerToggle;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.navigation_drawer_base_layout);
frameLayout = (FrameLayout)findViewById(R.id.content_frame);
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerList = (ListView) findViewById(R.id.left_drawer);
// set a custom shadow that overlays the main content when the drawer opens
//mDrawerLayout.setDrawerShadow(R.drawable.drawer_shadow, GravityCompat.START);
// set up the drawer's list view with items and click listener
mDrawerList.setAdapter(new ArrayAdapter<String>(this, R.layout.drawer_list_item, listArray));
mDrawerList.setOnItemClickListener(new OnItemClickListener()
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id)
openActivity(position);
);
// enable ActionBar app icon to behave as action to toggle nav drawer
getActionBar().setDisplayHomeAsUpEnabled(true);
getActionBar().setHomeButtonEnabled(true);
// ActionBarDrawerToggle ties together the the proper interactions between the sliding drawer and the action bar app icon
actionBarDrawerToggle = new ActionBarDrawerToggle(
this, /* host Activity */
mDrawerLayout, /* DrawerLayout object */
R.drawable.ic_launcher, /* nav drawer image to replace 'Up' caret */
R.string.drawer_open, /* "open drawer" description for accessibility */
R.string.drawer_close) /* "close drawer" description for accessibility */
@Override
public void onDrawerClosed(View drawerView)
getActionBar().setTitle(listArray[position]);
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
super.onDrawerClosed(drawerView);
@Override
public void onDrawerOpened(View drawerView)
getActionBar().setTitle(getString(R.string.app_name));
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
super.onDrawerOpened(drawerView);
@Override
public void onDrawerSlide(View drawerView, float slideOffset)
super.onDrawerSlide(drawerView, slideOffset);
@Override
public void onDrawerStateChanged(int newState)
super.onDrawerStateChanged(newState);
;
mDrawerLayout.setDrawerListener(actionBarDrawerToggle);
/**
* As we are calling BaseActivity from manifest file and this base activity is intended just to add navigation drawer in our app.
* We have to open some activity with layout on launch. So we are checking if this BaseActivity is called first time then we are opening our first activity.
* */
if(isLaunch)
/**
*Setting this flag false so that next time it will not open our first activity.
*We have to use this flag because we are using this BaseActivity as parent activity to our other activity.
*In this case this base activity will always be call when any child activity will launch.
*/
isLaunch = false;
openActivity(0);
/**
* @param position
*
* Launching activity when any list item is clicked.
*/
protected void openActivity(int position)
/**
* We can set title & itemChecked here but as this BaseActivity is parent for other activity,
* So whenever any activity is going to launch this BaseActivity is also going to be called and
* it will reset this value because of initialization in onCreate method.
* So that we are setting this in child activity.
*/
// mDrawerList.setItemChecked(position, true);
// setTitle(listArray[position]);
mDrawerLayout.closeDrawer(mDrawerList);
BaseActivity.position = position; //Setting currently selected position in this field so that it will be available in our child activities.
switch (position)
case 0:
startActivity(new Intent(this, SearchActivity.class));
break;
case 1:
startActivity(new Intent(this, SearchActivity.class));
break;
case 2:
startActivity(new Intent(this, SearchActivity.class));
break;
case 3:
startActivity(new Intent(this, SearchActivity.class));
break;
case 4:
startActivity(new Intent(this, SearchActivity.class));
break;
default:
break;
Toast.makeText(this, "Selected Item Position::"+position, Toast.LENGTH_LONG).show();
@Override
public boolean onCreateOptionsMenu(Menu menu)
getMenuInflater().inflate(R.menu.main, menu);
return super.onCreateOptionsMenu(menu);
@Override
public boolean onOptionsItemSelected(MenuItem item)
// The action bar home/up action should open or close the drawer.
// ActionBarDrawerToggle will take care of this.
if (actionBarDrawerToggle.onOptionsItemSelected(item))
return true;
switch (item.getItemId())
case R.id.action_settings:
return true;
default:
return super.onOptionsItemSelected(item);
/* Called whenever we call invalidateOptionsMenu() */
@Override
public boolean onPrepareOptionsMenu(Menu menu)
// If the nav drawer is open, hide action items related to the content view
boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
return super.onPrepareOptionsMenu(menu);
/* We can override onBackPressed method to toggle navigation drawer*/
@Override
public void onBackPressed()
if(mDrawerLayout.isDrawerOpen(mDrawerList))
mDrawerLayout.closeDrawer(mDrawerList);
else
mDrawerLayout.openDrawer(mDrawerList);
我的搜索活动：
import android.content.Context;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.os.Bundle;
import android.widget.ImageView;
public class SearchActivity extends BaseActivity
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
/**
* We will not use setContentView in this activty
* Rather than we will use layout inflater to add view in FrameLayout of our base activity layout*/
/**
* Adding our layout to parent class frame layout.
*/
getLayoutInflater().inflate(R.layout.activity_search, frameLayout);
/**
* Setting title and itemChecked
*/
mDrawerList.setItemChecked(position, true);
setTitle(listArray[position]);
//((ImageView)findViewById(R.id.image_view)).setBackgroundResource(R.drawable.image1);
drawer_list_item.xml：
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_
android:layout_
android:gravity="center_vertical"
android:paddingLeft="16dp"
android:paddingRight="16dp"
android:textColor="#fff"/>
还有我的 navigation_drawer_layout.xml：
<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/drawer_layout"
android:layout_
android:layout_ >
<FrameLayout
android:id="@+id/content_frame"
android:layout_
android:layout_ />
<ListView
android:id="@+id/left_drawer"
android:layout_
android:layout_
android:layout_gravity="start"
android:background="#111"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp" />
</android.support.v4.widget.DrawerLayout>
这是与我正在尝试做的事情相关的全部代码。
当我按下HomeActivity 内的signin 按钮时，出现以下错误：
01-06 13:39:45.563 17197-17197/guide_me_for_all.guide_me_for_all E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: guide_me_for_all.guide_me_for_all, PID: 17197
java.lang.RuntimeException: Unable to start activity ComponentInfoguide_me_for_all.guide_me_for_all/guide_me_for_all.guide_me_for_all.BaseActivity: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2212)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2271)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5146)
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:732)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:566)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at guide_me_for_all.guide_me_for_all.BaseActivity.onCreate(BaseActivity.java:92)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2169)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2271)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5146)
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:732)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:566)
at dalvik.system.NativeStart.main(Native Method)
【问题讨论】：
表示BaseActivity.java:92
就是这一行：getActionBar().setDisplayHomeAsUpEnabled(true);
getActionBar() 在您的代码中为空，如果您的 min sdk 低于 11，您需要使用 getSupportActionBar()，如果 min sdk 大于 11 检查主题，也许您删除或隐藏它，如果这对你搜索 ``getActionBar()` return null` 没有帮助，
您是否在您的主题中使用了动作栏应用战斗？因为如果你这样做了，那么你需要扩展 ActionBarActivity 然后使用 getSupportActionBar().setDisplayHomeAsUpEnabled(true);
我的 minsdk 是 16。我打开了 styles.xml 和 MyActionBar 样式，parent="@android:style/Widget.Holo.Light.ActionBar" 有错误，它无法解析这个符号。是否有可能我删除了与样式和属性相关的重要内容？因为许多其他 xml 文件在 @android ... e.t.c 上存在问题，所以我只是删除了它们的样式。但我不知道如何在我的项目中再次导入这些样式。
【参考方案1】：
您可能想尝试以下方法：
public class BaseActivity extends Activity
protected FrameLayout frameLayout;
protected ListView mDrawerList;
protected String[] listArray = "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" ;
private static boolean isLaunch = true;
private DrawerLayout mDrawerLayout;
private ActionBarDrawerToggle actionBarDrawerToggle;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.navigation_drawer_base_layout);
frameLayout = (FrameLayout)findViewById(R.id.content_frame);
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerList = (ListView) findViewById(R.id.left_drawer);
//mDrawerLayout.setDrawerShadow(R.drawable.drawer_shadow, GravityCompat.START);
mDrawerList.setAdapter(new ArrayAdapter<String>(this, R.layout.drawer_list_item, listArray));
mDrawerList.setOnItemClickListener(new OnItemClickListener()
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id)
openActivity(position);
getSupportActionBar().setTitle(listArray[position]);
);
getActionBar().setDisplayHomeAsUpEnabled(true);
getActionBar().setHomeButtonEnabled(true);
actionBarDrawerToggle = new ActionBarDrawerToggle(
this, /* host Activity */
mDrawerLayout, /* DrawerLayout object */
R.drawable.ic_launcher, /* nav drawer image to replace 'Up' caret */
R.string.drawer_open, /* "open drawer" description for accessibility */
R.string.drawer_close) /* "close drawer" description for accessibility */
@Override
public void onDrawerClosed(View drawerView)
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
super.onDrawerClosed(drawerView);
@Override
public void onDrawerOpened(View drawerView)
//use the support library in App Combat
getSupportActionBar().setTitle(getString(R.string.app_name));
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
super.onDrawerOpened(drawerView);
@Override
public void onDrawerSlide(View drawerView, float slideOffset)
super.onDrawerSlide(drawerView, slideOffset);
@Override
public void onDrawerStateChanged(int newState)
super.onDrawerStateChanged(newState);
;
mDrawerLayout.setDrawerListener(actionBarDrawerToggle);
//in the line below you will always get the Selected position 0 because your isLaunch = true, so it will always give you this toast. If you think its unessecary remove it.
if(isLaunch)
isLaunch = false;
openActivity(0);
由于 Navigation Drawer 可与 Fragments 一起使用，请尝试以下方法：
protected Fragment openActivity(int position)
mDrawerLayout.closeDrawer(mDrawerList);
Fragment fragment = null;
switch (position)
case 0:
fragment = new SearchActivity();
break;
case 1:
fragment = new A();
break;
case 2:
fragment = new B();
break;
case 3:
fragment = new C();
break;
case 4:
fragment = new D();
break;
FragmentManager fm = getSupportFragmentManager();
fm.beginTransaction().replace(R.id.content_frame, fragment).commit();
return fragment;
像这样使用onOptionsItemSelected 方法：
@Override
public boolean onCreateOptionsMenu(Menu menu)
getMenuInflater().inflate(R.menu.main, menu);
return super.onCreateOptionsMenu(menu);
@Override
public boolean onOptionsItemSelected(MenuItem item)
if (actionBarDrawerToggle.onOptionsItemSelected(item))
return true;
return super.onOptionsItemSelected(item);
onBackPressed 方法如下：
删除else语句，因为您不想按返回按钮并打开抽屉
/* We can override onBackPressed method to toggle navigation drawer*/
@Override
public void onBackPressed()
if(mDrawerLayout.isDrawerOpen(mDrawerList))
mDrawerLayout.closeDrawer(mDrawerList);
还将您的 SearchActivity 修改为片段，因为您希望在抽屉打开时成为第一个片段，如下所示：
public class SearchActivity extends Fragment
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
View convertView = null;
if(convertView == null)
convertView= getLayoutInflater(savedInstanceState).inflate(R.layout.activity_search, container, false);
return convertView;
希望对你有帮助！！！
【讨论】：
在onOptionsItemSelected我应该把这个放在最后吗？因为我得到一个错误，它没有回报。return super.onOptionsItemSelected(item);
我刚刚又编辑了一件东西。而不是 getActionBar().setTitle(getString(R.string.app_name));使用 getSupportActionBar().setTitle(getString(R.string.app_name));
一切正常。伟大和最重要的 EASY 解决方案。非常感谢！！【参考方案2】：
像这样在基本活动中覆盖 setContentView()。
@Override
public void setContentView(int layoutResID)
mDrawerLayout = (DrawerLayout) getLayoutInflater().inflate(
R.layout.activity_base, null);
mFrameLayout = (FrameLayout) mDrawerLayout
.findViewById(R.id.frame_container);
mDrawerList = (ExpandableListView) mDrawerLayout
.findViewById(R.id.left_drawer);
getLayoutInflater().inflate(layoutResID, mFrameLayout, true);
super.setContentView(mDrawerLayout);
//Your custom code
【讨论】：
我把它放在 cmets ` setContentView(R.layout.navigation_drawer_base_layout); ` 我在 onCreate 之外添加了您的代码，但更改了一些不同的名称。我没有添加任何其他代码。 部分错误：01-06 14:36:48.176 24882-24882/guide_me_for_all.guide_me_for_all E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: guide_me_for_all.guide_me_for_all, PID: 24882 java.lang.RuntimeException: Unable to start activity ComponentInfoguide_me_for_all.guide_me_for_all/guide_me_for_all.guide_me_for_all.BaseActivity: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2212) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2271) ... 【参考方案3】：
你能打电话吗
setContentView(R.layout.navigation_drawer_layout);
而不是
setContentView(R.layout.navigation_drawer_base_layout);
在BaseActivity?
此错误通常发生在您访问 findViewById 时出错。只需注释掉 mDrawerList.setItemChecked(position, true); 即可检查是否是问题所在。
【讨论】：
我没有布局：navigation_drawer_layout.xml。我还评论了您所说的那一行，但错误仍然存在：01-06 14:16:08.928 22231-22231/guide_me_for_all.guide_me_for_all E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: guide_me_for_all.guide_me_for_all, PID: 22231 java.lang.NullPointerException at guide_me_for_all.guide_me_for_all.BaseActivity.onPrepareOptionsMenu(BaseActivity.java:222) at android.app.Activity.onPreparePanel(Activity.java:2556) . . . 以上是关于具有多个活动的导航抽屉。 - 空指针异常的主要内容，如果未能解决你的问题，请参考以下文章
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