我在我的项目中应用导航抽屉。我要做的是在导航抽屉列表中添加三个项目,它们是FB_Fragment,TB_Fragment,G_fragment。当我点击这些项目中的任何一个时,它们各自的部分将会打开。所以我遇到的问题是当我运行我的项目时它会给我一个错误
" java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.abdul.navigation/com.example.abdul.navigation.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference "
"Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference "
MainActivity.java
package com.example.abdul.navigation;
import java.util.ArrayList;
import java.util.List;
import android.annotation.SuppressLint;
import android.app.ActionBar;
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.content.res.Configuration;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.app.ActivityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarActivity;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import com.example.abdul.navigation.FB_Fragment;
import android.widget.ListView;
import com.example.abdul.navigation.G_fragment;
import com.example.abdul.navigation.TB_Fragment;
public class MainActivity extends ActionBarActivity {
String[] menutitles; TypedArray menuIcons;
// nav drawer title
private CharSequence mDrawerTitle;
private CharSequence mTitle;
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;
private List<RowItem> rowItems;
private CustomAdapter adapter;
@SuppressLint("NewApi")
@Override protected void onCreate(Bundle savedInstanceState) {
setContentView(R.layout.activity_main);
mTitle = mDrawerTitle = getTitle();
menutitles = getResources().getStringArray(R.array.titles);
menuIcons = getResources().obtainTypedArray(R.array.icons);
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerList = (ListView) findViewById(R.id.slider_list);
rowItems = new ArrayList<RowItem>();
for (int i = 0; i < menutitles.length; i++) {
RowItem items = new RowItem(menutitles[i], menuIcons.getResourceId( i, -1));
rowItems.add(items);
}
menuIcons.recycle();
adapter = new CustomAdapter(getApplicationContext(), rowItems);
mDrawerList.setAdapter(adapter);
mDrawerList.setOnItemClickListener(new SlideitemListener());
// enabling action bar app icon and behaving it as toggle button
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setHomeButtonEnabled(true);
mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,R.drawable.ic_drawer, R.string.app_name,R.string.app_name)
{
public void onDrawerClosed(View view) {
getSupportActionBar().setTitle(mTitle);
// calling onPrepareOptionsMenu() to show action bar icons
ActivityCompat.invalidateOptionsMenu(getParent());
}
public void onDrawerOpened(View drawerView) {
getSupportActionBar().setTitle(mDrawerTitle);
// calling onPrepareOptionsMenu() to hide action bar icons
ActivityCompat.invalidateOptionsMenu(getParent());
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
if (savedInstanceState == null) {
// on first time display view for first nav item
updateDisplay(0);
}
}
class SlideitemListener implements ListView.OnItemClickListener {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id)
{ updateDisplay(position);
}
} private void updateDisplay(int position) {
Fragment fragment = null;
switch (position) {
case 0: fragment = new FB_Fragment();
break;
case 1: fragment = new G_fragment();
break;
case 2: fragment = new TB_Fragment();
break;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction().replace(R.id.frame_container, fragment).commit();
// update selected item and title, then close the drawer
setTitle(menutitles[position]);
mDrawerLayout.closeDrawer(mDrawerList);
}
else {
// error in creating fragment
Log.e("MainActivity", "Error in creating fragment");
}
}
@Override
public void setTitle(CharSequence title) {
mTitle = title;
getSupportActionBar().setTitle(mTitle);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// toggle nav drawer on selecting action bar app icon/title
if (mDrawerToggle.onOptionsItemSelected(item)) {
return true;
}
// Handle action bar actions click
switch (item.getItemId())
{
case
R.id.action_settings:
return true;
default:
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);
}
/** * 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 toggles
mDrawerToggle.onConfigurationChanged(newConfig);
}
}
CustomAdapter.java
package com.example.abdul.navigation;
import java.util.List;
import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
public class CustomAdapter extends BaseAdapter {
Context context; List<RowItem> rowItem;
CustomAdapter(Context context, List<RowItem> rowItem) {
this.context = context;
this.rowItem = rowItem;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
LayoutInflater mInflater = (LayoutInflater) context .getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
convertView = mInflater.inflate(R.layout.list_tem, null);
}
ImageView imgIcon = (ImageView) convertView.findViewById(R.id.icon);
TextView txtTitle = (TextView) convertView.findViewById(R.id.title);
RowItem row_pos = rowItem.get(position);
// setting the image resource and title
imgIcon.setImageResource(row_pos.getIcon());
txtTitle.setText(row_pos.getTitle());
return convertView;
}
@Override
public int getCount() {
return rowItem.size();
}
@Override
public Object getItem(int position) {
return rowItem.get(position);
}
@Override
public long getItemId(int position) {
return rowItem.indexOf(getItem(position));
}
}
Rowitem.java
package com.example.abdul.navigation;
public class RowItem {
private String title;
private int icon;
public RowItem(String title, int icon) {
this.title = title;
this.icon = icon;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public int getIcon() {
return icon;
}
public void setIcon(int icon) {
this.icon = icon;
}
}
FB_Fragment.java
package com.example.abdul.navigation;
import android.annotation.SuppressLint;
import android.app.Fragment;
import com.example.abdul.navigation.R;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
@SuppressLint("NewApi")
public class FB_Fragment extends Fragment {
@Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View rootView = inflater .inflate(R.layout.fb_fragment, container, false);
return rootView;
}
}
TB_Fragment.java
package com.example.abdul.navigation;
import android.annotation.SuppressLint;
import android.app.Fragment;
import com.example.abdul.navigation.R;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
@SuppressLint("NewApi")
public class TB_Fragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.tb_fragment, container, false);
return rootView;
}
}
G_fragment.java
package com.example.abdul.navigation;
import android.annotation.SuppressLint;
import android.app.Fragment;
import com.example.abdul.navigation.R;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
@SuppressLint("NewApi")
public class G_fragment extends Fragment {
@Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View rootView = inflater .inflate(R.layout.g_fragment, container, false);
return rootView;
}
}
activity_main.xml中
<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" >
<!-- The main content view -->
<FrameLayout
android:id="@+id/frame_container"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<!-- The navigation drawer list -->
<ListView
android:id="@+id/slider_list"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:background="#ffffff"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp" />
</android.support.v4.widget.DrawerLayout>
fb_fragment.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ImageView
android:id="@+id/imageView1"
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="148dp"
android:src="@drawable/fb" />
</RelativeLayout>
g_fragment.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ImageView
android:id="@+id/imageView1"
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="148dp"
android:src="@drawable/gplus" />
</RelativeLayout>
list_tem.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="48dp"
android:padding="5dp" >
<ImageView
android:id="@+id/icon"
android:layout_width="50dp"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:layout_marginLeft="12dp"
android:layout_marginRight="12dp"
android:contentDescription="@string/imgdesc" />
<TextView
android:id="@+id/title"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_marginTop="10dp"
android:layout_toRightOf="@id/icon"
android:gravity="center_vertical"
android:textColor="#000000"
android:textSize="20sp" />
</RelativeLayout>
tb_fragment.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ImageView
android:id="@+id/imageView1"
android:layout_width="100dp"
android:layout_height="100dp"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_marginTop="148dp"
android:src="@drawable/tb" />
</RelativeLayout>
的strings.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="app_name">Navigation</string>
<string name="hello_world">Hello world!</string>
<string name="action_settings">Settings</string>
<string name="imgdesc">imgdesc</string>
<string-array name="titles">
<item>Facebook</item>
<item>Google-Plus</item>
<item>TutorialsBuzz</item>
</string-array>
<array name="icons">
<item>@drawable/fb</item>
<item>@drawable/gplus</item>
<item>@drawable/tb</item>
</array>
</resources>
styles.xml
<resources>
<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<!-- Customize your theme here. -->
</style>
</resources>
答案 0 :(得分:3)
在支持库中ActionBar
使用
getSupportActionBar();
您正在使用getActionBar()
,因此它正在提供null
。
所以用getActionBar()
替换getSupportActionBar()
。
<强>更新
从styles.xml和中删除所有内容 在styles.xml中写下以下内容
<!--
Base application theme, dependent on API level. This theme is replaced
by AppBaseTheme from res/values-vXX/styles.xml on newer devices.
-->
<style name="AppBaseTheme" parent="Theme.AppCompat.Light">
<!--
Theme customizations available in newer API levels can go in
res/values-vXX/styles.xml, while customizations related to
backward-compatibility can go here.
-->
</style>
<!-- Application theme. -->
<style name="AppTheme" parent="AppBaseTheme">
<!-- All customizations that are NOT specific to a particular API-level can go here. -->
</style>
希望这会对你有所帮助。