java - getActionBar().setDisplayHomeAsUpEnabled(true) 上出现错误；

Question

package com.maya.helloandroid;

import java.util.ArrayList;
import android.app.Activity;
import android.content.res.Configuration;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.widget.DrawerLayout;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ListView;
import com.maya.helloandroid.adapter.NavDrawerListAdapter;
import com.maya.helloandroid.model.NavDrawerItem;

@SuppressWarnings("deprecation")
public class MainActivity extends Activity {


private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;

// nav drawer title
private CharSequence mDrawerTitle;

// used to store app title
private CharSequence mTitle;

// slide menu items
private String[] navMenuTitles;
private TypedArray navMenuIcons;

private ArrayList<NavDrawerItem> navDrawerItems;
private NavDrawerListAdapter adapter;

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

    //requestWindowFeature(Window.FEATURE_ACTION_BAR);

    setContentView(R.layout.activity_main);

    mTitle = mDrawerTitle = getTitle();

    // load slide menu items
    navMenuTitles=  
    getResources().getStringArray(R.array.nav_drawer_items);

    // nav drawer icons from resources
    navMenuIcons = getResources()
            .obtainTypedArray(R.array.nav_drawer_icons);

    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mDrawerList = (ListView) findViewById(R.id.list_slidermenu);

    navDrawerItems = new ArrayList<NavDrawerItem>();
    // adding nav drawer items to array
    // Home
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[0],   
navMenuIcons.getResourceId(0, -1)));
    // Find People
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], 
navMenuIcons.getResourceId(1, -1)));
    // Photos
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], 
navMenuIcons.getResourceId(2, -1)));
    // Communities, Will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], 
navMenuIcons.getResourceId(3, -1), true, "22"));
    // Pages
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[4], 
navMenuIcons.getResourceId(4, -1)));
    // What's hot, We  will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[5], 
navMenuIcons.getResourceId(5, -1), true, "50+"));

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

    // setting the nav drawer list adapter
    adapter = new NavDrawerListAdapter(getApplicationContext(),
            navDrawerItems);
    mDrawerList.setAdapter(adapter);

    // enabling action bar app icon and behaving it as toggle button

    getActionBar().setDisplayHomeAsUpEnabled(true);
    getActionBar().setHomeButtonEnabled(true);

    mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
            R.drawable.ic_drawer, //nav menu toggle icon
            R.string.app_name, // nav drawer open - description for 
accessibility
            R.string.app_name // nav drawer close - description for 
accessibility
    ){
        public void onDrawerClosed(View view) {
            getActionBar().setTitle(mTitle);
            // calling onPrepareOptionsMenu() to show action bar icons
            invalidateOptionsMenu();
        }

        public void onDrawerOpened(View drawerView) {
            getActionBar().setTitle(mDrawerTitle);
            // calling onPrepareOptionsMenu() to hide action bar icons
            invalidateOptionsMenu();
        }
    };
    mDrawerLayout.setDrawerListener(mDrawerToggle);

    /*if (savedInstanceState == null) {
        // on first time display view for first nav item
        displayView(0);
    }
*/
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is 
present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

  /* Called when invalidateOptionsMenu() is triggered
     */
    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        // if nav drawer is opened, hide the action items
        boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
        menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
        return super.onPrepareOptionsMenu(menu);
    }


    @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);
    }
}

我的 style.xml 包含:

style name="AppBaseTheme" parent="Theme.AppCompat.Light.DarkActionBar"

我的 Android list 包含:

android:minSdkVersion="14" 
android:targetSdkVersion="21" 

由于上述情况，我的应用程序不幸停止了，并收到此错误:

08-17 12:23:58.069: E/AndroidRuntime(15535): Caused by: java.lang.NullPointerException 08-17 12:23:58.069: E/AndroidRuntime(15535): at com.maya.helloandroid.MainActivity.onCreate(MainActivity.java:85)

在这一行:

getActionBar().setDisplayHomeAsUpEnabled(true);

请帮我解决这个问题。

Answer 1

避免 Activity 使用 AppcompatActivity 或 ActionBarActivity 而不是 Activity 。

按照这里可能可以解决您的问题。 getActionBar().setDisplayHomeAsUpEnabled(true); throws NullPointerException on new activity creation (Google - Basic Tutorial) getActionBar().setDisplayHomeAsUpEnabled(true) throws NullPointerException