Android中的导航抽屉空指针异常
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【中文标题】Android中的导航抽屉空指针异常【英文标题】:Navigation Drawer Null Pointer Exception in Android 【发布时间】:2015-01-10 06:14:33 【问题描述】:在 android 中获取空指针异常 在下面发布我的代码以及 logcat 的屏幕截图(错误) MainActivity.java
package com.example.wabco;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.widget.DrawerLayout;
import android.view.Gravity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class MainActivity extends Activity
// Within which the entire activity is enclosed
private DrawerLayout mDrawerLayout;
// ListView represents Navigation Drawer
private ListView mDrawerList;
// ActionBarDrawerToggle indicates the presence of Navigation Drawer in the action bar
private ActionBarDrawerToggle mDrawerToggle;
// Title of the action bar
private String mTitle = "";
@SuppressLint("NewApi")
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mTitle = "JAVATECHIG.COM";
getActionBar().setTitle(mTitle);
// Getting reference to the DrawerLayout
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerList = (ListView) findViewById(R.id.drawer_list);
// Getting reference to the ActionBarDrawerToggle
mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
R.drawable.ic_drawer, R.string.drawer_open,
R.string.drawer_close)
/** Called when drawer is closed */
public void onDrawerClosed(View view)
getActionBar().setTitle(mTitle);
invalidateOptionsMenu();
/** Called when a drawer is opened */
public void onDrawerOpened(View drawerView)
getActionBar().setTitle("JAVATECHIG.COM");
invalidateOptionsMenu();
;
// Setting DrawerToggle on DrawerLayout
mDrawerLayout.setDrawerListener(mDrawerToggle);
// Creating an ArrayAdapter to add items to the listview mDrawerList
ArrayAdapter<String> adapter = new ArrayAdapter<String>(getBaseContext(),
R.layout.drawer_list_item, getResources().getStringArray(R.array.menus));
// Setting the adapter on mDrawerList
mDrawerList.setAdapter(adapter);
// Enabling Home button
getActionBar().setHomeButtonEnabled(true);
// Enabling Up navigation
getActionBar().setDisplayHomeAsUpEnabled(true);
// Setting item click listener for the listview mDrawerList
mDrawerList.setOnItemClickListener(new OnItemClickListener()
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id)
// Getting an array of rivers
String[] menuItems = getResources().getStringArray(R.array.menus);
// Currently selected river
mTitle = menuItems[position];
// Creating a fragment object
WebViewFragment rFragment = new WebViewFragment();
// Passing selected item information to fragment
Bundle data = new Bundle();
data.putInt("position", position);
data.putString("url", getUrl(position));
rFragment.setArguments(data);
// Getting reference to the FragmentManager
FragmentManager fragmentManager = getFragmentManager();
// Creating a fragment transaction
FragmentTransaction ft = fragmentManager.beginTransaction();
// Adding a fragment to the fragment transaction
ft.replace(R.id.content_frame, rFragment);
// Committing the transaction
ft.commit();
// Closing the drawer
mDrawerLayout.closeDrawer(mDrawerList);
);
protected String getUrl(int position)
switch (position)
case 0:
return "http://javatechig.com";
case 1:
return "http://javatechig.com/category/android/";
case 2:
return "http://javatechig.com/category/blackberry/";
case 3:
return "http://javatechig.com/category/j2me/";
case 4:
return "http://javatechig.com/category/sencha-touch/";
case 5:
return "http://javatechig.com/category/phonegap/";
case 6:
return "http://javatechig.com/category/java/";
default:
return "http://javatechig.com";
@Override
protected void onPostCreate(Bundle savedInstanceState)
super.onPostCreate(savedInstanceState);
mDrawerToggle.syncState();
@Override
public boolean onOptionsItemSelected(MenuItem item)
if (mDrawerToggle.onOptionsItemSelected(item))
return true;
return super.onOptionsItemSelected(item);
/** Called whenever we call invalidateOptionsMenu() */
@Override
public boolean onPrepareOptionsMenu(Menu menu)
// If the drawer is open, hide action items related to the content view
boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
return super.onPrepareOptionsMenu(menu);
@Override
public boolean onCreateOptionsMenu(Menu menu)
getMenuInflater().inflate(R.menu.main, menu);
return true;
添加布局和菜单代码 activity_main.xml
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/drawer_layout"
android:layout_
android:layout_ >
<!-- The main content view -->
<FrameLayout
android:id="@+id/content_frame"
android:layout_
android:layout_ />
<!-- The navigation drawer -->
<ListView
android:id="@+id/drawer_list"
android:layout_
android:layout_
android:layout_gravity="start"
android:background="#111"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp" />
</android.support.v4.widget.DrawerLayout>
drawer_list_item.xml
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@android:id/text1"
android:layout_
android:layout_
android:background="?android:attr/activatedBackgroundIndicator"
android:gravity="center_vertical"
android:minHeight="?android:attr/listPreferredItemHeightSmall"
android:paddingLeft="16dp"
android:paddingRight="16dp"
android:textAppearance="?android:attr/textAppearanceListItemSmall"
android:textColor="#fff" />
fragment_layout.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_
android:layout_
android:orientation="vertical" >
<WebView
android:id="@+id/webView"
android:layout_
android:layout_ />
</LinearLayout>
菜单 main.xml
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
tools:context="com.example.wabco.MainActivity" >
<item
android:id="@+id/action_settings"
android:orderInCategory="100"
android:title="@string/action_settings"
app:showAsAction="ifRoom"/>
</menu>
【问题讨论】:
您尝试过扩展ActionBarActivity
而不是Activity
吗?
尝试改变 getActionBar().setTitle(mTitle);使用 getSupportActionBar().setTitle(mTitle);
如果我使用 getSupportActionBar 进行更改,我会收到一个错误 MainActivity 类型的方法 getSupportActionBar() 未定义。
你应该像@ρяσѕρєяK所说的那样扩展ActionBarActivity
。
对于以后的发布,您应该复制错误 logcat 输出并粘贴它们,而不是 logcat 输出的屏幕截图。
【参考方案1】:
对上面的代码进行下面提到的更改,它可以正常工作,
MainActivity 将“Activity”扩展为“ActionBarActivity”。
所有“getActionBar()”到“getSupportActionBar()”
注意:导入android.support.v7.app.ActionBarActivity
【讨论】:
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