我正在编写一个具有导航抽屉的应用程序。我希望其中一个片段中有一张地图。
我的MainActivity使用方法selectItem在framgents之间切换。
这是我的MainActivity.java：
package de.illner.android.locationapi.maps;
import android.content.res.Configuration;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class MainActivity extends FragmentActivity {
private String[] mMenuTitles;
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;
private CharSequence mNavTitle;
private CharSequence mTitle;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mTitle = mNavTitle = getTitle();
mMenuTitles = getResources().getStringArray(R.array.menu_entries);
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, mMenuTitles));
mDrawerList.setOnItemClickListener(new DrawerItemClickListener());
// 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
mDrawerToggle = new ActionBarDrawerToggle( this, /* host Activity */
mDrawerLayout, /* DrawerLayout object */
R.drawable.ic_drawer, /* 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 */
) {
public void onDrawerClosed(View view) {
getActionBar().setTitle(mTitle);
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
}
public void onDrawerOpened(View drawerView) {
getActionBar().setTitle(mNavTitle);
invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
if (savedInstanceState == null) {
selectItem(0);
}
}
@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 (mDrawerToggle.onOptionsItemSelected(item)) {
return true;
}
else {
return super.onOptionsItemSelected(item);
}
}
/* The click listner for ListView in the navigation drawer */
private class DrawerItemClickListener implements ListView.OnItemClickListener {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
selectItem(position);
}
}
private void selectItem(int position) {
// update the main content by replacing fragments
Fragment fragment = null;
//"Meine Aktuelle Position"
if (position == 0)
{
fragment = new PositionFragment();
Bundle args = new Bundle();
args.putInt(PositionFragment.ARG_ENTRY_NUMBER, position);
fragment.setArguments(args);
}
//"Melden (automatisch)" || "Melden (manuell)" || "Meine Meldungen verwalten"
else if (position == 1 || position == 2 || position == 3)
{
fragment = new VerificationFragment();
Bundle args = new Bundle();
args.putInt(VerificationFragment.ARG_ENTRY_NUMBER, position);
fragment.setArguments(args);
}
//"Meldungen zu Zeitpunkt"
else if (position == 4)
{
}
//"Über diese App"
else if (position == 5)
{
}
else
{
//position nicht in gültigem Bereich!
}
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();
// update selected item and title, then close the drawer
mDrawerList.setItemChecked(position, true);
setTitle(mMenuTitles[position]);
mDrawerLayout.closeDrawer(mDrawerList);
}
@Override
public void setTitle(CharSequence title) {
mTitle = title;
getActionBar().setTitle(mTitle);
}
/**
* When using the ActionBarDrawerToggle, you must call it during
* onPostCreate() and onConfigurationChanged()...
*/
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
// Sync the toggle state after onRestoreInstanceState has occurred.
mDrawerToggle.syncState();
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
// Pass any configuration change to the drawer toggls
mDrawerToggle.onConfigurationChanged(newConfig);
}
}
这是带有NavigationDrawer的MainActivity的布局文件activity_main.xml：
<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">
<FrameLayout
android:id="@+id/content_frame"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<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>
这是我的地图碎片，应该从头开始。
PositionFragment.java：
package de.illner.android.locationapi.maps;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
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 PositionFragment extends Fragment {
public static final String ARG_ENTRY_NUMBER = "entry_number";
static final LatLng HAMBURG = new LatLng(53.558, 9.927);
static final LatLng KIEL = new LatLng(53.551, 9.993);
private GoogleMap map;
public PositionFragment() {
// Empty constructor required for fragment subclasses
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_position, container, false);
int i = getArguments().getInt(ARG_ENTRY_NUMBER);
String entryTitle = getResources().getStringArray(R.array.menu_entries)[i];
getActivity().setTitle(entryTitle);
map = ((SupportMapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();
Marker hamburg = map.addMarker(new MarkerOptions().position(HAMBURG)
.title("Hamburg"));
Marker kiel = map.addMarker(new MarkerOptions()
.position(KIEL)
.title("Kiel")
.snippet("Kiel is cool")
.icon(BitmapDescriptorFactory
.fromResource(R.drawable.ic_launcher)));
// Move the camera instantly to hamburg with a zoom of 15.
map.moveCamera(CameraUpdateFactory.newLatLngZoom(HAMBURG, 15));
// Zoom in, animating the camera.
map.animateCamera(CameraUpdateFactory.zoomTo(10), 2000, null);
return rootView;
}
@Override
public void onDestroyView() {
SupportMapFragment f = (SupportMapFragment) getFragmentManager()
.findFragmentById(R.id.content_frame);
if (f != null) {
try {
getFragmentManager().beginTransaction().remove(f).commit();
} catch (Exception e) {
e.printStackTrace();
}
}
super.onDestroyView();
}
}
这里是必须在开头切换到的片段的布局：
fragment_position.xml：
<?xml version="1.0" encoding="utf-8"?>
<fragment
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/map"
android:layout_width="match_parent"
android:layout_height="match_parent"
class="com.google.android.gms.maps.MapFragment" />
如果我想启动我的应用程序，我会在此行中获得NullPointerException：
map = ((SupportMapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();
我认为问题出在activity_main.xml或fragment_position.xml。
如果我想要启动另一个片段（没有地图），它会完美运行。
感谢所有人帮助我解决我可能的小故障;）
这是日志：
04-01 16:34:45.393: E/AndroidRuntime(3723): FATAL EXCEPTION: main
04-01 16:34:45.393: E/AndroidRuntime(3723): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.illner.android.locationapi.maps/de.illner.android.locationapi.maps.MainActivity}: java.lang.NullPointerException
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2339)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2389)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.app.ActivityThread.access$600(ActivityThread.java:153)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1269)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.os.Handler.dispatchMessage(Handler.java:99)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.os.Looper.loop(Looper.java:137)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.app.ActivityThread.main(ActivityThread.java:5289)
04-01 16:34:45.393: E/AndroidRuntime(3723): at java.lang.reflect.Method.invokeNative(Native Method)
04-01 16:34:45.393: E/AndroidRuntime(3723): at java.lang.reflect.Method.invoke(Method.java:525)
04-01 16:34:45.393: E/AndroidRuntime(3723): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739)
04-01 16:34:45.393: E/AndroidRuntime(3723): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
04-01 16:34:45.393: E/AndroidRuntime(3723): at dalvik.system.NativeStart.main(Native Method)
04-01 16:34:45.393: E/AndroidRuntime(3723): Caused by: java.lang.NullPointerException
04-01 16:34:45.393: E/AndroidRuntime(3723): at de.illner.android.locationapi.maps.PositionFragment.onCreateView(PositionFragment.java:40)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:570)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.app.Activity.performStart(Activity.java:5143)
04-01 16:34:45.393: E/AndroidRuntime(3723): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2302)
04-01 16:34:45.393: E/AndroidRuntime(3723): ... 11 more
答案 0 :(得分：0)
我有一个类似的问题，只需等待加载地图即可解决。它有时需要一些时间才能正确加载。尝试这样的事情：
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
@Override
public void run() {
// Get map as you do in your code
if(map != null) {
// Map loaded, precede as usual
} else {
// Keep delaying until the map is loaded.
handler.postDelayed(this, 200);
}
}
}, 200);
希望这会有所帮助：）