我已经构建了一个新活动（.Notitie），试图将相同的菜单作为主要活动（.MainActivity）。但它给出了一个致命的例外::
01-14 08:24:05.756 12945-12945/nl.verpleegkundigzakboek.www.verpleegkundigzakboek E/AndroidRuntime: FATAL EXCEPTION: main
Process: nl.verpleegkundigzakboek.www.verpleegkundigzakboek, PID: 12945
java.lang.RuntimeException: Unable to start activity ComponentInfo{nl.verpleegkundigzakboek.www.verpleegkundigzakboek/nl.verpleegkundigzakboek.www.verpleegkundigzakboek.Notities}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
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:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at nl.verpleegkundigzakboek.www.verpleegkundigzakboek.Notities.onCreate(Notities.java:64)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
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:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
它说它的原因是：java.lang.NullPointerException at nl.verpleegkundigzakboek.www.verpleegkundigzakboek.Notities.onCreate（Notities.java:64）
所以我猜问题就在于这段代码：
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
getLoaderManager().initLoader(0, null, this);
来自我的Notities活动：
package nl.verpleegkundigzakboek.www.verpleegkundigzakboek;
import android.app.AlertDialog;
import android.app.LoaderManager;
import android.content.ContentValues;
import android.content.CursorLoader;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.CursorAdapter;
import android.widget.ListView;
import android.widget.Toast;
public class Notities extends AppCompatActivity
implements LoaderManager.LoaderCallbacks<Cursor>, NavigationView.OnNavigationItemSelectedListener {
NavigationView navigationView = null;
Toolbar toolbar = null;
private static final int EDITOR_REQUEST_CODE = 1001;
private CursorAdapter cursorAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_notities);
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
cursorAdapter = new NotesCursorAdapter(this, null, 0);
ListView list = (ListView) findViewById(android.R.id.list);
list.setAdapter(cursorAdapter);
list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Intent intent = new Intent(Notities.this, EditorActivity.class);
Uri uri = Uri.parse(NotesProvider.CONTENT_URI + "/" + id);
intent.putExtra(NotesProvider.CONTENT_ITEM_TYPE, uri);
startActivityForResult(intent, EDITOR_REQUEST_CODE);
}
});
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
getLoaderManager().initLoader(0, null, this);
}
private void insertNote(String noteText) {
ContentValues values = new ContentValues();
values.put(DBOpenhelper.NOTE_TEXT, noteText);
Uri noteUri = getContentResolver().insert(NotesProvider.CONTENT_URI,
values);
Log.d("Notities", "Inserted note " + noteUri.getLastPathSegment());
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@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_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
switch (id) {
case R.id.action_create_sample:
insertSampleData();
break;
case R.id.action_delete_all:
deleteAllNotes();
break;
}
return super.onOptionsItemSelected(item);
}
private void deleteAllNotes() {
DialogInterface.OnClickListener dialogClickListener =
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int button) {
if (button == DialogInterface.BUTTON_POSITIVE) {
//Insert Data management code here
getContentResolver().delete(
NotesProvider.CONTENT_URI, null, null
);
restartLoader();
Toast.makeText(Notities.this,
getString(R.string.all_deleted),
Toast.LENGTH_SHORT).show();
}
}
};
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage(getString(R.string.are_you_sure))
.setPositiveButton(getString(android.R.string.yes), dialogClickListener)
.setNegativeButton(getString(android.R.string.no), dialogClickListener)
.show();
}
private void insertSampleData() {
insertNote("Simple note");
insertNote("Multi-line\nnote");
insertNote("Very long note with a lot of text that exceeds the width of the screen");
restartLoader();
}
private void restartLoader() {
getLoaderManager().restartLoader(0, null, this);
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
return new CursorLoader(this, NotesProvider.CONTENT_URI,
null, null, null, null);
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
cursorAdapter.swapCursor(data);
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
cursorAdapter.swapCursor(null);
}
public void openEditorForNewNote(View view) {
Intent intent = new Intent(this, EditorActivity.class);
startActivityForResult(intent, EDITOR_REQUEST_CODE);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == EDITOR_REQUEST_CODE && resultCode == RESULT_OK) {
restartLoader();
}
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
if (id == R.id.nav_camera) {
//set the fragment initially
MainFragment fragment = new MainFragment();
android.support.v4.app.FragmentTransaction fragmentTransaction =
getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, fragment);
fragmentTransaction.commit();
//handle the camera action
} else if (id == R.id.nav_gallery) {
Zakkaartjes fragment = new Zakkaartjes();
android.support.v4.app.FragmentTransaction fragmentTransaction =
getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, fragment);
fragmentTransaction.commit();
} else if (id == R.id.nav_slideshow) {
Rekenen fragment = new Rekenen();
android.support.v4.app.FragmentTransaction fragmentTransaction =
getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, fragment);
fragmentTransaction.commit();
} else if (id == R.id.nav_manage) {
Intent intent = new Intent(this, Notities.class);
startActivity(intent);
finish();
} else if (id == R.id.nav_share) {
Protocollen fragment = new Protocollen();
android.support.v4.app.FragmentTransaction fragmentTransaction =
getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, fragment);
fragmentTransaction.commit();
} else if (id == R.id.nav_send) {
Intent emailIntent = new Intent(Intent.ACTION_SENDTO, Uri.fromParts(
"mailto","info@verpleegkundigzakboek.nl", null));
emailIntent.putExtra(Intent.EXTRA_SUBJECT, "Email van verpleegkundig zakboek app");
startActivity(Intent.createChooser(emailIntent, "Verzend e-mail"));
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
}
添加了我的activity_notities：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".Notities">
<ListView
android:id="@+id/android:list"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<at.markushi.ui.CircleButton
android:layout_width="64dp"
android:layout_height="64dp"
app:cb_color="@color/primary"
app:cb_pressedRingWidth="8dp"
android:layout_alignParentBottom="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:src="@drawable/ic_action_add"
android:onClick="openEditorForNewNote"/>
<include
layout="@layout/app_bar_notities"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<android.support.design.widget.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="@layout/nav_header_main"
app:menu="@menu/activity_main_drawer" />
<!--<Button-->
<!--android:id="@+id/button"-->
<!--android:layout_width="wrap_content"-->
<!--android:layout_height="wrap_content"-->
<!--android:layout_alignParentBottom="true"-->
<!--android:layout_alignParentEnd="true"-->
<!--android:layout_alignParentRight="true"-->
<!--android:onClick="openEditorForNewNote"-->
<!--android:text="New note" />-->
希望有人可以给我一个提示？！
grtzzz
答案 0 :(得分：0)
在您的activity_notities.xml文件中，您似乎错过了您尝试在以下行中引用的抽屉布局（ drawer_layout ）：
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
此行期望您的导航抽屉布局为android:id="@+id/drawer_layout"。因为在xml文件中没有这样的布局drawer为空。
以下是从Android Developers site获取的drawerLayout的示例：
<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">
<!-- The main content view -->
<FrameLayout
android:id="@+id/content_frame"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<!-- The navigation drawer -->
<ListView android:id="@+id/left_drawer"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp"
android:background="#111"/>
</android.support.v4.widget.DrawerLayout>