当我按下链接到片段活动的活动按钮（Tab +滑动导航）时出现崩溃。
这是MenuActivity.java类（我有按钮的Activity）：
package com.touchscreentable;
import smart.weable.R;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageButton;
public class MainMenu extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_menu);
addListenerOnButton();
}
ImageButton b1;
public void addListenerOnButton() {
final Context context = this;
b1 = (ImageButton) findViewById(R.id.imageButton1);
b1.setOnClickListener(new View.OnClickListener() {
public void onClick(View arg0) {
Intent intent = new Intent(MainMenu.this, SecondMenu.class);
startActivity(intent);
}
});
}
}
这是main_menu布局，我的MainMenu.java活动的布局：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:background="#ffffff" >
<!-- width: 768; heith: 195 -->
<ImageButton
android:id="@+id/imageButton1"
android:layout_width="1536px"
android:layout_height="390px"
android:background="@null"
android:src="@drawable/button1" />
这是SecondMenu.java，一个FragmentActivity：
package com.touchscreentable;
import java.util.Locale;
import smart.weable.R;
import smart.weable.R.id;
import smart.weable.R.layout;
import smart.weable.R.menu;
import smart.weable.R.string;
import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.NavUtils;
import android.support.v4.view.ViewPager;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class SecondMenu extends FragmentActivity implements
ActionBar.TabListener {
/**
* The {@link android.support.v4.view.PagerAdapter} that will provide
* fragments for each of the sections. We use a
* {@link android.support.v4.app.FragmentPagerAdapter} derivative, which
* will keep every loaded fragment in memory. If this becomes too memory
* intensive, it may be best to switch to a
* {@link android.support.v4.app.FragmentStatePagerAdapter}.
*/
SectionsPagerAdapter mSectionsPagerAdapter;
/**
* The {@link ViewPager} that will host the section contents.
*/
ViewPager mViewPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.second_menu);
// Set up the action bar.
final ActionBar actionBar = getActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Create the adapter that will return a fragment for each of the three
// primary sections of the app.
mSectionsPagerAdapter = new SectionsPagerAdapter(
getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mSectionsPagerAdapter);
// When swiping between different sections, select the corresponding
// tab. We can also use ActionBar.Tab#select() to do this if we have
// a reference to the Tab.
mViewPager.setOnPageChangeListener(newViewPager.SimpleOnPageChangeListener() {
@Override
public void onPageSelected(int position) {
actionBar.setSelectedNavigationItem(position);
}
});
// For each of the sections in the app, add a tab to the action bar.
for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
// Create a tab with text corresponding to the page title defined by
// the adapter. Also specify this Activity object, which implements
// the TabListener interface, as the callback (listener) for when
// this tab is selected.
actionBar.addTab(actionBar.newTab()
.setText(mSectionsPagerAdapter.getPageTitle(i))
.setTabListener(this));
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.second_menu, menu);
return true;
}
@Override
public void onTabSelected(ActionBar.Tab tab,
FragmentTransaction fragmentTransaction) {
// When the given tab is selected, switch to the corresponding page in
// the ViewPager.
mViewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(ActionBar.Tab tab,
FragmentTransaction fragmentTransaction) {
}
@Override
public void onTabReselected(ActionBar.Tab tab,
FragmentTransaction fragmentTransaction) {
}
/**
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a DummySectionFragment (defined as a static inner class
// below) with the page number as its lone argument.
Fragment fragment = new DummySectionFragment();
Bundle args = new Bundle();
args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
fragment.setArguments(args);
return fragment;
}
@Override
public int getCount() {
// Show 3 total pages.
return 3;
}
@Override
public CharSequence getPageTitle(int position) {
Locale l = Locale.getDefault();
switch (position) {
case 0:
return getString(R.string.title_section1).toUpperCase(l);
case 1:
return getString(R.string.title_section2).toUpperCase(l);
case 2:
return getString(R.string.title_section3).toUpperCase(l);
}
return null;
}
}
/**
* A dummy fragment representing a section of the app, but that simply
* displays dummy text.
*/
public static class DummySectionFragment extends Fragment {
public static final String ARG_SECTION_NUMBER = "section_number";
public DummySectionFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(
R.layout.fragment_second_menu_dummy, container,false);
TextView dummyTextView = (TextView) rootView
.findViewById(R.id.section_label);
dummyTextView.setText(Integer.toString(getArguments().getInt(
ARG_SECTION_NUMBER)));
return rootView;
}
}
}
这是FragmentActivity（second_menu.xml）的布局：
<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".SecondMenu" />
这是fragment_second_menu_dummy.xml：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".SecondMenu$DummySectionFragment" >
<TextView
android:id="@+id/section_label"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
这是Manifest.xml文件（包含所有活动）：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="smart.weable"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="14"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@android:style/Theme.NoTitleBar.Fullscreen" >
<activity
android:name="com.touchscreentable.WelcomeScreen"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.touchscreentable.MainMenu"
android:label="@string/app_name" >
</activity>
<activity
android:name="com.touchscreentable.SecondMenu"
android:label="@string/title_activity_second_menu" >
</activity>
</application>
最后这里是LogCat错误跟踪：
06-30 13:07:57.650: E/AndroidRuntime(20465): FATAL EXCEPTION: main
06-30 13:07:57.650: E/AndroidRuntime(20465): java.lang.RuntimeException: Unable to start activity ComponentInfo{smart.weable/com.touchscreentable.SecondMenu}: java.lang.NullPointerException
06-30 13:07:57.650: E/AndroidRuntime(20465): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
06-30 13:07:57.650: E/AndroidRuntime(20465): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
06-30 13:07:57.650: E/AndroidRuntime(20465): at android.app.ActivityThread.access$600(ActivityThread.java:130)
06-30 13:07:57.650: E/AndroidRuntime(20465): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
06-30 13:07:57.650: E/AndroidRuntime(20465): at android.os.Handler.dispatchMessage(Handler.java:99)
06-30 13:07:57.650: E/AndroidRuntime(20465): at android.os.Looper.loop(Looper.java:137)
06-30 13:07:57.650: E/AndroidRuntime(20465): at android.app.ActivityThread.main(ActivityThread.java:4745)
06-30 13:07:57.650: E/AndroidRuntime(20465): at java.lang.reflect.Method.invokeNative(Native Method)
06-30 13:07:57.650: E/AndroidRuntime(20465): at java.lang.reflect.Method.invoke(Method.java:511)
06-30 13:07:57.650: E/AndroidRuntime(20465): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:810)
06-30 13:07:57.650: E/AndroidRuntime(20465): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:577)
06-30 13:07:57.650: E/AndroidRuntime(20465): at dalvik.system.NativeStart.main(Native Method)
06-30 13:07:57.650: E/AndroidRuntime(20465): Caused by: java.lang.NullPointerException
06-30 13:07:57.650: E/AndroidRuntime(20465): at com.touchscreentable.SecondMenu.onCreate(SecondMenu.java:53)
06-30 13:07:57.650: E/AndroidRuntime(20465): at android.app.Activity.performCreate(Activity.java:5008)
06-30 13:07:57.650: E/AndroidRuntime(20465): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
06-30 13:07:57.650: E/AndroidRuntime(20465): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
06-30 13:07:57.650: E/AndroidRuntime(20465): ... 11 more
所以，我的问题非常简单。当我按下按钮“b1”从MainMenu.java导航到SecondMenu.java时，为什么应用程序会崩溃？
我连续3天在互联网上搜索，我无法解释。求救！