我正在尝试实现导航抽屉并在多个活动中使用它。但是当我尝试启动另一个活动时（当我点击导航抽屉中的项目时），应用程序崩溃并显示强制关闭消息。 这是我的主要活动，名为Home：
package com.radoslav.socialreminder;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;
public class Home extends AppCompatActivity
implements NavigationDrawerCallbacks {
/**
* Fragment managing the behaviors, interactions and presentation of the navigation drawer.
*/
private NavigationDrawerFragment mNavigationDrawerFragment;
private Toolbar mToolbar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home_new);
mToolbar = (Toolbar) findViewById(R.id.toolbar_actionbar);
setSupportActionBar(mToolbar);
mNavigationDrawerFragment = (NavigationDrawerFragment)
getFragmentManager().findFragmentById(R.id.fragment_drawer);
// Set up the drawer.
mNavigationDrawerFragment.setup(R.id.fragment_drawer, (DrawerLayout) findViewById(R.id.drawer), mToolbar);
}
@Override
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
Toast.makeText(this, "Menu item selected -> " + position, Toast.LENGTH_SHORT).show();
Intent intent;
if(position == 0)
{
}
else if(position == 1)
{
try {
intent = new Intent(Home.this, MyTasks.class);
startActivity(intent);
}
catch (Exception e)
{
System.out.println("exception occurred: " + e);
}
}
else if(position == 2)
{
intent = new Intent(Home.this, Group_tasks.class);
startActivity(intent);
}
else if(position == 3)
{
intent = new Intent(Home.this, What_do_I_miss.class);
startActivity(intent);
}
else
{
Toast.makeText(this, "An error has occurred!", Toast.LENGTH_LONG).show();
}
}
@Override
public void onBackPressed() {
if (mNavigationDrawerFragment.isDrawerOpen())
mNavigationDrawerFragment.closeDrawer();
else
super.onBackPressed();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
if (!mNavigationDrawerFragment.isDrawerOpen()) {
// Only show items in the action bar relevant to this screen
// if the drawer is not showing. Otherwise, let the drawer
// decide what to show in the action bar.
getMenuInflater().inflate(R.menu.home_new, menu);
return true;
}
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
这是我的界面：
package com.radoslav.socialreminder;
public interface NavigationDrawerCallbacks {
void onNavigationDrawerItemSelected(int position);
}
NavigationDrawerAdapter：
package com.radoslav.socialreminder;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.util.List;
public class NavigationDrawerAdapter extends RecyclerView.Adapter<NavigationDrawerAdapter.ViewHolder> {
private List<NavigationItem> mData;
private NavigationDrawerCallbacks mNavigationDrawerCallbacks;
private View mSelectedView;
private int mSelectedPosition;
public NavigationDrawerAdapter(List<NavigationItem> data) {
mData = data;
}
public NavigationDrawerCallbacks getNavigationDrawerCallbacks() {
return mNavigationDrawerCallbacks;
}
public void setNavigationDrawerCallbacks(NavigationDrawerCallbacks navigationDrawerCallbacks) {
mNavigationDrawerCallbacks = navigationDrawerCallbacks;
}
@Override
public NavigationDrawerAdapter.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
View v = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.drawer_row, viewGroup, false);
final ViewHolder viewHolder = new ViewHolder(v);
viewHolder.itemView.setClickable(true);
viewHolder.itemView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (mSelectedView != null) {
mSelectedView.setSelected(false);
}
mSelectedPosition = viewHolder.getPosition();
v.setSelected(true);
mSelectedView = v;
if (mNavigationDrawerCallbacks != null)
mNavigationDrawerCallbacks.onNavigationDrawerItemSelected(viewHolder.getPosition());
}
}
);
viewHolder.itemView.setBackgroundResource(R.drawable.row_selector);
return viewHolder;
}
@Override
public void onBindViewHolder(NavigationDrawerAdapter.ViewHolder viewHolder, int i) {
viewHolder.textView.setText(mData.get(i).getText());
viewHolder.textView.setCompoundDrawablesWithIntrinsicBounds(mData.get(i).getDrawable(), null, null, null);
if (mSelectedPosition == i) {
if (mSelectedView != null) {
mSelectedView.setSelected(false);
}
mSelectedPosition = i;
mSelectedView = viewHolder.itemView;
mSelectedView.setSelected(true);
}
}
public void selectPosition(int position) {
mSelectedPosition = position;
notifyItemChanged(position);
}
@Override
public int getItemCount() {
return mData != null ? mData.size() : 0;
}
public static class ViewHolder extends RecyclerView.ViewHolder {
public TextView textView;
public ViewHolder(View itemView) {
super(itemView);
textView = (TextView) itemView.findViewById(R.id.item_name);
}
}
}
和NavigationDrawerFragment：
package com.radoslav.socialreminder;
import android.app.Activity;
import android.app.Fragment;
import android.content.SharedPreferences;
import android.content.res.Configuration;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import java.lang.String;
import java.util.ArrayList;
import java.util.List;
/**
* Fragment used for managing interactions for and presentation of a navigation drawer.
* See the <a href="https://developer.android.com/design/patterns/navigation-drawer.html#Interaction">
* design guidelines</a> for a complete explanation of the behaviors implemented here.
*/
public class NavigationDrawerFragment extends Fragment implements NavigationDrawerCallbacks {
/**
* Remember the position of the selected item.
*/
private static final String STATE_SELECTED_POSITION = "selected_navigation_drawer_position";
/**
* Per the design guidelines, you should show the drawer on launch until the user manually
* expands it. This shared preference tracks this.
*/
private static final String PREF_USER_LEARNED_DRAWER = "navigation_drawer_learned";
/**
* A pointer to the current callbacks instance (the Activity).
*/
private NavigationDrawerCallbacks mCallbacks;
/**
* Helper component that ties the action bar to the navigation drawer.
*/
private ActionBarDrawerToggle mActionBarDrawerToggle;
private DrawerLayout mDrawerLayout;
private RecyclerView mDrawerList;
private View mFragmentContainerView;
private int mCurrentSelectedPosition = 0;
private boolean mFromSavedInstanceState;
private boolean mUserLearnedDrawer;
private String item1 = "Home";
private String item2 = "My tasks";
private String item3 = "Group tasks";
private String item4 = "What do I miss?";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
System.out.println(item1);
// Read in the flag indicating whether or not the user has demonstrated awareness of the
// drawer. See PREF_USER_LEARNED_DRAWER for details.
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getActivity());
mUserLearnedDrawer = sp.getBoolean(PREF_USER_LEARNED_DRAWER, false);
if (savedInstanceState != null) {
mCurrentSelectedPosition = savedInstanceState.getInt(STATE_SELECTED_POSITION);
mFromSavedInstanceState = true;
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_navigation_drawer_new, container, false);
mDrawerList = (RecyclerView) view.findViewById(R.id.drawerList);
LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
mDrawerList.setLayoutManager(layoutManager);
mDrawerList.setHasFixedSize(true);
final List<NavigationItem> navigationItems = getMenu();
NavigationDrawerAdapter adapter = new NavigationDrawerAdapter(navigationItems);
adapter.setNavigationDrawerCallbacks(this);
mDrawerList.setAdapter(adapter);
selectItem(mCurrentSelectedPosition);
return view;
}
public boolean isDrawerOpen() {
return mDrawerLayout != null && mDrawerLayout.isDrawerOpen(mFragmentContainerView);
}
public ActionBarDrawerToggle getActionBarDrawerToggle() {
return mActionBarDrawerToggle;
}
public DrawerLayout getDrawerLayout() {
return mDrawerLayout;
}
@Override
public void onNavigationDrawerItemSelected(int position) {
selectItem(position);
}
public List<NavigationItem> getMenu() {
List<NavigationItem> items = new ArrayList<NavigationItem>();
items.add(new NavigationItem(item1, getResources().getDrawable(R.drawable.ic_menu_check)));
items.add(new NavigationItem(item2, getResources().getDrawable(R.drawable.ic_menu_check)));
items.add(new NavigationItem(item3, getResources().getDrawable(R.drawable.ic_menu_check)));
items.add(new NavigationItem(item4, getResources().getDrawable(R.drawable.ic_menu_check)));
return items;
}
/**
* Users of this fragment must call this method to set up the navigation drawer interactions.
*
* @param fragmentId The android:id of this fragment in its activity's layout.
* @param drawerLayout The DrawerLayout containing this fragment's UI.
* @param toolbar The Toolbar of the activity.
*/
public void setup(int fragmentId, DrawerLayout drawerLayout, Toolbar toolbar) {
mFragmentContainerView = getActivity().findViewById(fragmentId);
mDrawerLayout = drawerLayout;
mDrawerLayout.setStatusBarBackgroundColor(getResources().getColor(R.color.myPrimaryDarkColor));
mActionBarDrawerToggle = new ActionBarDrawerToggle(getActivity(), mDrawerLayout, toolbar, R.string.drawer_open, R.string.drawer_close) {
@Override
public void onDrawerClosed(View drawerView) {
super.onDrawerClosed(drawerView);
if (!isAdded()) return;
getActivity().invalidateOptionsMenu(); // calls onPrepareOptionsMenu()
}
@Override
public void onDrawerOpened(View drawerView) {
super.onDrawerOpened(drawerView);
if (!isAdded()) return;
if (!mUserLearnedDrawer) {
mUserLearnedDrawer = true;
SharedPreferences sp = PreferenceManager
.getDefaultSharedPreferences(getActivity());
sp.edit().putBoolean(PREF_USER_LEARNED_DRAWER, true).apply();
}
getActivity().invalidateOptionsMenu(); // calls onPrepareOptionsMenu()
}
};
// If the user hasn't 'learned' about the drawer, open it to introduce them to the drawer,
// per the navigation drawer design guidelines.
if (!mUserLearnedDrawer && !mFromSavedInstanceState) {
mDrawerLayout.openDrawer(mFragmentContainerView);
}
// Defer code dependent on restoration of previous instance state.
mDrawerLayout.post(new Runnable() {
@Override
public void run() {
mActionBarDrawerToggle.syncState();
}
});
mDrawerLayout.setDrawerListener(mActionBarDrawerToggle);
}
private void selectItem(int position) {
mCurrentSelectedPosition = position;
if (mDrawerLayout != null) {
mDrawerLayout.closeDrawer(mFragmentContainerView);
}
if (mCallbacks != null) {
mCallbacks.onNavigationDrawerItemSelected(position);
}
((NavigationDrawerAdapter) mDrawerList.getAdapter()).selectPosition(position);
}
public void openDrawer() {
mDrawerLayout.openDrawer(mFragmentContainerView);
}
public void closeDrawer() {
mDrawerLayout.closeDrawer(mFragmentContainerView);
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
mCallbacks = (NavigationDrawerCallbacks) activity;
} catch (ClassCastException e) {
throw new ClassCastException("Activity must implement NavigationDrawerCallbacks.");
}
}
@Override
public void onDetach() {
super.onDetach();
mCallbacks = null;
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt(STATE_SELECTED_POSITION, mCurrentSelectedPosition);
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
// Forward the new configuration the drawer toggle component.
mActionBarDrawerToggle.onConfigurationChanged(newConfig);
}
}
这是应用程序崩溃时logcat吐出的内容：
08-07 14:42:16.765 941-941/com.radoslav.socialreminder I/System.out﹕ Home
08-07 14:42:16.775 941-941/com.radoslav.socialreminder D/AndroidRuntime﹕ Shutting down VM
08-07 14:42:16.775 941-941/com.radoslav.socialreminder W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41b30700)
08-07 14:42:16.790 941-941/com.radoslav.socialreminder E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.radoslav.socialreminder/com.radoslav.socialreminder.MyTasks}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2295)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
at android.app.ActivityThread.access$700(ActivityThread.java:159)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:176)
at android.app.ActivityThread.main(ActivityThread.java:5419)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:94)
at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:87)
at android.support.v7.internal.app.ToolbarActionBar.<init>(ToolbarActionBar.java:79)
at android.support.v7.app.AppCompatDelegateImplV7.setSupportActionBar(AppCompatDelegateImplV7.java:198)
at android.support.v7.app.AppCompatActivity.setSupportActionBar(AppCompatActivity.java:96)
at com.radoslav.socialreminder.MyTasks.onCreate(MyTasks.java:26)
at android.app.Activity.performCreate(Activity.java:5372)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2257)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
at android.app.ActivityThread.access$700(ActivityThread.java:159)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:176)
at android.app.ActivityThread.main(ActivityThread.java:5419)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132)
at dalvik.system.NativeStart.main(Native Method)
08-07 14:42:16.795 2430-2780/? I/ActivityManager﹕ Notify an ApplicationCrash
答案 0 :(得分：0)
谢谢，这是MyTasks.class，但我已经注释了大部分内容
package com.radoslav.socialreminder;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
public class MyTasks extends ActionBarActivity{
// implements NavigationDrawerCallbacks {
/**
* Fragment managing the behaviors, interactions and presentation of the navigation drawer.
*/
private NavigationDrawerFragment mNavigationDrawerFragment;
private Toolbar mToolbar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_tasks);
/* mToolbar = (Toolbar) findViewById(R.id.toolbar_actionbar);
setSupportActionBar(mToolbar);
mNavigationDrawerFragment = (NavigationDrawerFragment)
getFragmentManager().findFragmentById(R.id.fragment_drawer);
// Set up the drawer.
mNavigationDrawerFragment.setup(R.id.fragment_drawer, (DrawerLayout) findViewById(R.id.drawer), mToolbar);*/
}
/* @Override
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
Toast.makeText(this, "Menu item selected -> " + position, Toast.LENGTH_SHORT).show();
}
@Override
public void onBackPressed() {
if (mNavigationDrawerFragment.isDrawerOpen())
mNavigationDrawerFragment.closeDrawer();
else
super.onBackPressed();
}
*/
@Override
public boolean onCreateOptionsMenu(Menu menu) {
if (!mNavigationDrawerFragment.isDrawerOpen()) {
// Only show items in the action bar relevant to this screen
// if the drawer is not showing. Otherwise, let the drawer
// decide what to show in the action bar.
getMenuInflater().inflate(R.menu.home_new, menu);
return true;
}
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}