虽然我不是编程新手，但我是Android新手，而且我一直在处理我正在处理的应用程序的问题。
该应用是使用Google Maps Api的地图。我得到了那个工作，并决定我想要一个精美的抽屉导航配合它。这并不是那么顺利。
我可以看到错误是第74行，但我无法弄清楚如何处理它。我找了很多同样问题的人，但他们的理由似乎与我的不同之处在于收到这个错误。
这里的第74和第75行，这些都是错误的原因：
mDrawerList.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mDrawerListItems));
mDrawerList.setOnItemClickListener(new AdapterView.OnItemClickListener()
这里有一切：
package com.example.lehi.byu_idahomaps;
import android.content.res.Configuration;
import android.os.Bundle;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.widget.Toolbar;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import android.widget.PopupMenu;
import android.view.MenuInflater;
import com.google.android.gms.maps.CameraUpdate;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;
public class MapsActivity extends ActionBarActivity implements PopupMenu.OnMenuItemClickListener {
// Locations for all buildings on campus.
private final LatLng LOCATION_CAMPUS = new LatLng(43.815489, -111.783012);
private final LatLng LOCATION_SMITH = new LatLng(43.819230, -111.781481);
private final LatLng LOCATION_HART = new LatLng(43.819780, -111.785261);
private final LatLng LOCATION_RICKS = new LatLng(43.815120, -111.781303);
private final LatLng LOCATION_AUSTIN = new LatLng(43.816018, -111.784543);
private final LatLng LOCATION_ICENTER = new LatLng(43.818782, -111.785176);
private final LatLng LOCATION_BENSON = new LatLng(43.815569, -111.783255);
private final LatLng LOCATION_CLARKE = new LatLng(43.820492, -111.781796);
private final LatLng LOCATION_HEALTH = new LatLng(43.817017, -111.779275);
private final LatLng LOCATION_HINCKLEY = new LatLng(43.816080, -111.779876);
private final LatLng LOCATION_KIMBALL = new LatLng(43.817249, -111.781506);
private final LatLng LOCATION_KIRKHAM = new LatLng(43.821336, -111.781657);
private final LatLng LOCATION_MC = new LatLng(43.818619, -111.782611);
private final LatLng LOCATION_MCKAY = new LatLng(43.819587, -111.783159);
private final LatLng LOCATION_ROMNEY = new LatLng(43.820423, -111.783148);
private final LatLng LOCATION_SNOW = new LatLng(43.821414, -111.783652);
private final LatLng LOCATION_SPORI = new LatLng(43.821019, -111.782300);
private final LatLng LOCATION_TAYLOR = new LatLng(43.817171, -111.782408);
// Our map
private GoogleMap map; // Might be null if Google Play services APK is not available.
// Our marker object
Marker marker;
DrawerLayout mDrawerLayout;
ListView mDrawerList;
ActionBarDrawerToggle mDrawerToggle;
String[] mDrawerListItems;
//Creates the map, sets it to the campus location, and turns on your location
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
map = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();
CameraUpdate start = CameraUpdateFactory.newLatLngZoom(LOCATION_CAMPUS, 15);
map.moveCamera(start);
map.setMyLocationEnabled(true);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer);
mDrawerList = (ListView)findViewById(android.R.id.list);
mDrawerListItems = getResources().getStringArray(R.array.drawer_list);
mDrawerList.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mDrawerListItems));
mDrawerList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
int editedPosition = position + 1;
Toast.makeText(MapsActivity.this, "You selected item " + editedPosition, Toast.LENGTH_SHORT).show();
mDrawerLayout.closeDrawer(mDrawerList);
}
});
mDrawerToggle = new ActionBarDrawerToggle(this,
mDrawerLayout,
toolbar,
R.string.drawer_open,
R.string.drawer_close) {
public void onDrawerClosed(View v) {
super.onDrawerClosed(v);
invalidateOptionsMenu();
syncState();
}
public void onDrawerOpened(View v) {
super.onDrawerOpened(v);
invalidateOptionsMenu();
syncState();
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setHomeButtonEnabled(true);
mDrawerToggle.syncState();
}
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
mDrawerToggle.syncState();
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
mDrawerToggle.onConfigurationChanged(newConfig);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home: {
if (mDrawerLayout.isDrawerOpen(mDrawerList)) {
mDrawerLayout.closeDrawer(mDrawerList);
} else {
mDrawerLayout.openDrawer(mDrawerList);
}
return true;
}
default:
return super.onOptionsItemSelected(item);
}
}
public void showPopUp(View v) {
PopupMenu popup = new PopupMenu(this, v);
popup.setOnMenuItemClickListener(MapsActivity.this);
MenuInflater inflater = popup.getMenuInflater();
inflater.inflate(R.menu.popup, popup.getMenu());
popup.show();
}
@Override
protected void onResume() {
super.onResume();
}
@Override
public boolean onMenuItemClick(MenuItem item) {
CameraUpdate update;
switch (item.getItemId()) {
case R.id.austin:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_AUSTIN, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_AUSTIN)
.title("Mark Austin")
.snippet("College of Physical Sciences & Engineering"));
map.animateCamera(update);
return true;
case R.id.icenter:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_ICENTER, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_ICENTER)
.title("BYU-I Center"));
map.animateCamera(update);
return true;
case R.id.benson:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_BENSON, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_BENSON)
.title("Ezra Taft Benson")
.snippet("College of Agriculture and Life Sciences"));
map.animateCamera(update);
return true;
case R.id.clarke:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_CLARKE, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_CLARKE)
.title("John L. Clarke"));
map.animateCamera(update);
return true;
case R.id.hart:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_HART, 19);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_HART)
.title("John W. Hart"));
map.animateCamera(update);
return true;
case R.id.health:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_HEALTH, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_HEALTH)
.title("Student Health Center"));
map.animateCamera(update);
return true;
case R.id.hinckley:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_HINCKLEY, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_HINCKLEY)
.title("Gordan B. Hinckley")
.snippet("College of Education & Human Development"));
map.animateCamera(update);
return true;
case R.id.kimball:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_KIMBALL, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_KIMBALL)
.title("Spencer W. Kimball"));
map.animateCamera(update);
return true;
case R.id.kirkham:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_KIRKHAM, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_KIRKHAM)
.title("Oscar A. Kirkham"));
map.animateCamera(update);
return true;
case R.id.mc:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_MC, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_MC)
.title("Hyrum Manwaring"));
map.animateCamera(update);
return true;
case R.id.mckay:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_MCKAY, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_MCKAY)
.title("David O. McKay Library"));
map.animateCamera(update);
return true;
case R.id.ricks:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_RICKS, 19);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_RICKS)
.title("Thomas E. Ricks"));
map.animateCamera(update);
return true;
case R.id.romney:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_ROMNEY, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_ROMNEY)
.title("George S. Romney"));
map.animateCamera(update);
return true;
case R.id.smith:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_SMITH, 19);
map.animateCamera(update);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_SMITH)
.title("Joseph Fielding Smith")
.snippet("College of Business and Communication\n" +
"College of Language & Letters"));
return true;
case R.id.snow:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_SNOW, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_SNOW)
.title("Eliza R. Snow"));
map.animateCamera(update);
return true;
case R.id.spori:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_SPORI, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_SPORI)
.title("Jacob Spori")
.snippet("College of Performing & Visual Arts"));
map.animateCamera(update);
return true;
case R.id.taylor:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_TAYLOR, 18);
marker = map.addMarker(new MarkerOptions()
.position(LOCATION_TAYLOR)
.title("Taylor"));
map.animateCamera(update);
return true;
default:
if (marker != null) {
marker.remove();
}
map.setMapType(GoogleMap.MAP_TYPE_NORMAL);
update = CameraUpdateFactory.newLatLngZoom(LOCATION_CAMPUS, 15);
map.animateCamera(update);
return true;
}
}
}
这是我的activity_maps.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MapsActivity"
android:orientation="vertical">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
xmlns:android="http://schemas.android.com/apk/res/android" />
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/drawer"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MapsActivity"
android:clickable="false"
android:background="#2a6ebb"
android:orientation="vertical">
<ImageButton
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/btnmenu"
android:layout_width="71dp"
android:layout_height="65dp"
android:src="@drawable/abc_ic_menu_moreoverflow_mtrl_alpha"
android:onClick="showPopUp"
android:background="#2a6ebb"
android:contentDescription="Slide out menu button" />
<TextView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="wrap_content"
android:layout_height="53dp"
android:id="@+id/edittext"
android:gravity="center_vertical|center_horizontal"
android:text="BYU-I Maps"
android:textSize="35sp"
android:textIsSelectable="false"
android:layout_gravity="center_horizontal"
android:layout_above="@+id/map"
android:layout_centerHorizontal="true"
android:layout_alignParentTop="true" />
<fragment
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/map"
android:name="com.google.android.gms.maps.MapFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@+id/btnmenu" />
</RelativeLayout>
<FrameLayout
android:id="@+id/content_frame"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<ListView
android:id="@+id/list"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:background="#111"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp" />
</android.support.v4.widget.DrawerLayout>
</LinearLayout>
这是血腥的错误：
03-06 16:46:51.836 15778-15778/com.example.lehi.byu_idahomaps E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.lehi.byu_idahomaps, PID: 15778
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.lehi.byu_idahomaps/com.example.lehi.byu_idahomaps.MapsActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2438)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2497)
at android.app.ActivityThread.access$900(ActivityThread.java:168)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1306)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5678)
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:1291)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.lehi.byu_idahomaps.MapsActivity.onCreate(MapsActivity.java:74)
at android.app.Activity.performCreate(Activity.java:5586)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1093)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2402)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2497)
at android.app.ActivityThread.access$900(ActivityThread.java:168)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1306)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:146)
at android.app.ActivityThread.main(ActivityThread.java:5678)
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:1291)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
at dalvik.system.NativeStart.main(Native Method)
感谢您的帮助！
答案 0 :(得分：1)
mDrawerList = (ListView)findViewById(android.R.id.list);
应改为：
mDrawerList = (ListView)findViewById(R.id.list);
还删除ID为content_frame的FrameLayout DrawerLayout应包含一个内容View（Group）和一个列表或片段（将成为抽屉）
答案 1 :(得分：0)
删除{}中的android.：
mDrawerList = (ListView)findViewById(android.R.id.list);
这将导致：
mDrawerList = (ListView)findViewById(R.id.list);