由于我对此缺乏了解，我从一个问题跳到另一个问题。我一直试图弄清楚它几个小时，并查看以前的各种问题，但没有到达任何地方。最近出现了这个错误：
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.widget.DrawerLayout.setDrawerShadow(int, int)' on a null object reference
at XXXX.NavigationDrawerFragment.setUp(NavigationDrawerFragment.java:136)
at XXXX.EditFactFind.onCreate(EditFactFind.java:72)
at android.app.Activity.performCreate(Activity.java:5990)
我的Activity（它失败的要点）是：
import java.io.Serializable;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import android.app.ActionBar;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.widget.DrawerLayout;
//import android.support.v7.app.ActionBar;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class EditFactFind extends Activity implements NavigationDrawerFragment.NavigationDrawerCallbacks {
public static final int RESULT_DELETE = -500;
private boolean isInEditMode = true;
private boolean isAddingFactFind = true;
private NavigationDrawerFragment mNavigationDrawerFragment;
private CharSequence mTitle;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.edit_factfind);
final Button saveButton = (Button)findViewById(R.id.saveButton);
final Button cancelButton = (Button)findViewById(R.id.cancelButton);
final EditText titleEditText = (EditText)findViewById(R.id.titleEditText);
//final EditText factFindEditText = (EditText)findViewById(R.id.factFindEditText);
final TextView dateTextView = (TextView)findViewById(R.id.dateTextView);
final Button nextButton =(Button) findViewById(R.id.nextButton);
//Create fragment and give it an argument for the selected article
secA_pg1 iniSecFrag = new secA_pg1();
Bundle args = new Bundle();
args.putInt(secA_pg1.ARG_INDEX, 1);
iniSecFrag.setArguments(args);
FragmentTransaction initialTransaction = getFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack so the user can navigate back
initialTransaction.replace(R.id.fragment_container, iniSecFrag);
initialTransaction.addToBackStack(null);
//Commit the transaction
initialTransaction.commit();
mNavigationDrawerFragment = (NavigationDrawerFragment)
getFragmentManager().findFragmentById(R.id.navigation_drawer);
mTitle = getTitle();
// Set up the drawer.
mNavigationDrawerFragment.setUp(
R.id.navigation_drawer,
(DrawerLayout) findViewById(R.id.drawer_layout));
Serializable extra = getIntent().getSerializableExtra("FactFind");
if(extra != null)
{
FactFind factFind = (FactFind) extra;
titleEditText.setText(factFind.getTitle());
// factFindEditText.setText(factFind.getFactFindTitle());
DateFormat dateFormat = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss");
String date = dateFormat.format(factFind.getDate());
dateTextView.setText(date);
isInEditMode = false;
titleEditText.setEnabled(false);
// factFindEditText.setEnabled(false);
saveButton.setText("Edit");
isAddingFactFind = false;
}
cancelButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
setResult(RESULT_CANCELED, new Intent());
finish();
}
});
nextButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
//secA_pg1 secFrag = (secA_pg1) getFragmentManager().findFragmentById(R.id.Sec_A_pg1_fragment);
//Create fragment and give it an argument for the selected article
secA_pg2 newSecFrag = new secA_pg2();
Bundle args = new Bundle();
args.putInt(secA_pg2.ARG_INDEX, 2);
newSecFrag.setArguments(args);
FragmentTransaction transaction = getFragmentManager().beginTransaction();
// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack so the user can navigate back
transaction.replace(R.id.fragment_container, newSecFrag);
transaction.addToBackStack(null);
//Commit the transaction
transaction.commit();
}
});
saveButton.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
if(isInEditMode)
{
Intent returnIntent = new Intent();
FactFind factFind = new FactFind(titleEditText.getText().toString(),Calendar.getInstance().getTime());
returnIntent.putExtra("FactFind", factFind);
setResult(RESULT_OK, returnIntent);
finish();
}
else
{
isInEditMode = true;
saveButton.setText("Save");
titleEditText.setEnabled(true);
// factFindEditText.setEnabled(true);
}
}
});
}
我的Navigation抽屉失败了setUp方法：
package XXXX;
import android.support.v4.app.FragmentActivity;
import android.app.ActionBar;
//import android.support.v7.app.ActionBar;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.AppCompatActivity;
import android.app.Activity;
import android.app.Fragment;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.content.SharedPreferences;
import android.content.res.Configuration;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import android.support.v7.widget.Toolbar;
public void setUp(int fragmentId, DrawerLayout drawerLayout) {
mFragmentContainerView = getActivity().findViewById(fragmentId);
mDrawerLayout = drawerLayout;
// 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
ActionBar actionBar = getActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
actionBar.setHomeButtonEnabled(true);
// ActionBarDrawerToggle ties together the the proper interactions
// between the navigation drawer and the action bar app icon.
mDrawerToggle = new ActionBarDrawerToggle(
getActivity(), /* host Activity */
mDrawerLayout, /* DrawerLayout object */
R.drawable.ic_drawer, /* nav drawer image to replace 'Up' caret */
R.string.navigation_drawer_open, /* "open drawer" description for accessibility */
R.string.navigation_drawer_close /* "close drawer" description for accessibility */
) {
@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) {
// The user manually opened the drawer; store this flag to prevent auto-showing
// the navigation drawer automatically in the future.
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() {
mDrawerToggle.syncState();
}
});
mDrawerLayout.setDrawerListener(mDrawerToggle);
}
抽屉的XML是
<!-- A DrawerLayout is intended to be used as the top-level content view using match_parent for both width and height to consume the full space available. -->
<android.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="XXXX.MainActivity">
<!-- As the main content view, the view below consumes the entire
space available using match_parent in both dimensions. -->
<FrameLayout
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<!-- android:layout_gravity="start" tells DrawerLayout to treat
this as a sliding drawer on the left side for left-to-right
languages and on the right side for right-to-left languages.
If you're not building against API 17 or higher, use
android:layout_gravity="left" instead. -->
<!-- The drawer is given a fixed width in dp and extends the full height of
the container. -->
<fragment
android:id="@+id/navigation_drawer"
android:layout_width="@dimen/navigation_drawer_width"
android:layout_height="match_parent"
android:layout_gravity="start"
android:name="XXXX.NavigationDrawerFragment"
tools:layout="@layout/fragment_navigation_drawer" />
</android.DrawerLayout>
我假设mDrawerLayout未被正确拾取并因此返回null但我无法弄清楚为什么会这样。
感谢。