Question

这是主要的活动java文件。我得到了错误 java.lang.NullPointerException：尝试调用虚方法＆＃39; voidandroid.widget.ListView.setOnItemClickListener（android.widget.AdapterView $ OnItemClickListener）＆＃39;在null对象引用上在com.example.dell.syncytium.MainActivity.onCreate（MainActivity.java:76）

import android.app.Fragment;
import android.app.FragmentManager;
import android.content.res.Configuration;
import android.content.res.TypedArray;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBar;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;

import android.widget.AdapterView;
import android.widget.ListView;

import com.example.dell.syncytium.Fragments.AboutUsFragment;
import com.example.dell.syncytium.Fragments.Contact;
import com.example.dell.syncytium.Fragments.Events;
import com.example.dell.syncytium.Fragments.HomeFragment;
import com.example.dell.syncytium.Fragments.Register;
import com.example.dell.syncytium.Fragments.Sponsors;

import java.util.ArrayList;
public class MainActivity extends ActionBarActivity {
      DrawerLayout mDrawerLayout;
      ListView mListView;
      ActionBarDrawerToggle mBarToggle;
      private CharSequence mtitle;
      private CharSequence mDrawerTitle;

private String[] navMenuTitles;
private TypedArray navMenuIcons;

private ArrayList<NavDrawerItem> navDrawerItems;
private NavDrawerAdapter navDrawerAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    mtitle=mDrawerTitle=getTitle();
    navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);
    navMenuIcons = getResources()
            .obtainTypedArray(R.array.nav_drawer_icons);

    mDrawerLayout = (DrawerLayout)findViewById(R.id.drawerLayout);
    mListView = (ListView)findViewById(R.id.navDrawerView);
    navDrawerItems = new ArrayList<NavDrawerItem>();
    // adding nav drawer items to array

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons.getResourceId(3, -1)));

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[4], navMenuIcons.getResourceId(4, -1)));

    navDrawerItems.add(new NavDrawerItem(navMenuTitles[5], navMenuIcons.getResourceId(5, -1)));


    // Recycle the typed array
    navMenuIcons.recycle();

    mListView.setOnItemClickListener(new SlideMenuClickListener());
    navDrawerAdapter = new NavDrawerAdapter(getApplicationContext(), navDrawerItems);
    mListView.setAdapter(navDrawerAdapter);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    getSupportActionBar().setHomeButtonEnabled(true);

    mBarToggle =
            new ActionBarDrawerToggle
    (this,mDrawerLayout,R.string.app_name,R.string.app_name)
            {
                public void onDrawerClosed(View view){
                    getSupportActionBar().setTitle(mDrawerTitle);
                    invalidateOptionsMenu();
                }
                public void onDrawerOpened(View view){
                    getSupportActionBar().setTitle(mtitle);
                    invalidateOptionsMenu();
                }
            };
    mDrawerLayout.setDrawerListener(mBarToggle);
    if(savedInstanceState == null){
        displayView(0);
    }
}
private class SlideMenuClickListener implements
        ListView.OnItemClickListener {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
                            long id) {
        // display view for selected nav drawer item
        displayView(position);
    }
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_main,menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if (mBarToggle.onOptionsItemSelected(item)){
    return true;
    }
    switch (item.getItemId()){
        case R.id.action_settings:
            return true;
        default:return super.onOptionsItemSelected(item);
    }
}
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    boolean drawerOpen = mDrawerLayout.isDrawerOpen(mListView);
    menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
    return super.onPrepareOptionsMenu(menu);
}

private void displayView(int position) {
    // update the main content by replacing fragments
    Fragment fragment = null;
    switch (position) {
        case 0:
            fragment = new HomeFragment();
            break;
        case 1:
            fragment = new AboutUsFragment();
            break;
        case 2:
            fragment = new Events();
            break;
        case 3:
            fragment = new Sponsors();
            break;
        case 4:
            fragment = new Contact();
            break;
        case 5:
            fragment = new Register();
            break;

        default:
            break;
    }

    if (fragment != null) {
        FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.frameContainer, fragment).commit();

        // update selected item and title, then close the drawer
        mListView.setItemChecked(position, true);
        mListView.setSelection(position);
        setTitle(navMenuTitles[position]);
        mDrawerLayout.closeDrawer(mListView);
    } else {
        // error in creating fragment
        Log.e("MainActivity", "Error in creating fragment");
    }
}
@Override
public void setTitle(CharSequence title) {
    mDrawerTitle = title;
    getSupportActionBar().setTitle(mDrawerTitle);
}
    @Override
protected void onPostCreate(Bundle savedInstanceState) {
    super.onPostCreate(savedInstanceState);
    mBarToggle.syncState();
}

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    mBarToggle.onConfigurationChanged(newConfig);

}

}

这里是主要的activity.xml

 <android.support.v4.widget.DrawerLayout
 xmlns:android="http://schemas.android.com/apk/res/android"
 android:id = "@+id/drawerLayout"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 >
 <FrameLayout
    android:id = "@+id/frameContainer"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

 </FrameLayout>

 <ListView
    android:id="@+id/navDrawerView"
    android:layout_width="240dp"
    android:layout_height="match_parent"
    android:layout_gravity = "start"
    android:choiceMode="singleChoice"
    android:divider="@color/background_material_light"
    android:dividerHeight="1dp"
    android:background="@color/bright_foreground_material_dark">

</ListView>

Answer 1

我认为你对listview使用了错误的标识符：navDrawerView

Answer 2

您必须使用setContentView方法拨打onCreate。

我的应用程序在发布时崩溃了

2 个答案: