コードは次のとおりです。
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, b2, b3, b4, b5;
public void addListenerOnButton() {
final Context context = this;
b1 = (ImageButton) findViewById(R.id.imageButton1);
b2 = (ImageButton) findViewById(R.id.imageButton2);
b3 = (ImageButton) findViewById(R.id.imageButton3);
b4 = (ImageButton) findViewById(R.id.imageButton4);
b5 = (ImageButton) findViewById(R.id.imageButton5);
b1.setOnClickListener(new View.OnClickListener() {
public void onClick(View arg0) {
Intent intent = new Intent(context, ThirdMenu.class);
startActivity(intent);
}
});
}
イメージボタン「b1」を押すとクラッシュします。これは、ナビゲートしたい「ThirdMenu」です(タブスワイプアクティビティ):
public class ThirdMenu extends FragmentActivity {
/**
* 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.third_menu);
// Show the Up button in the action bar.
getActionBar().setDisplayHomeAsUpEnabled(true);
// 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);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.third_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* 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 {
/**
* The fragment argument representing the section number for this
* 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_third_menu_dummy, container, false);
TextView dummyTextView = (TextView) rootView
.findViewById(R.id.section_label);
dummyTextView.setText(Integer.toString(getArguments().getInt(
ARG_SECTION_NUMBER)));
return rootView;
}
}
}
これは Android マニフェスト ファイルです。
<?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/app_name" >
</activity>
<activity
android:name="com.touchscreentable.ThirdMenu"
android:label="@string/title_activity_third_menu"
android:parentActivityName="com.touchscreentable.MainMenu" >
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.touchscreentable.MainMenu" />
</activity>
</application>
</manifest>
これは logcat エラーです:
06-28 09:57:11.720: E/AndroidRuntime(10569): FATAL EXCEPTION: main
06-28 09:57:11.720: E/AndroidRuntime(10569): java.lang.RuntimeException: Unable to start activity ComponentInfo{smart.weable/com.touchscreentable.ThirdMenu}: java.lang.NullPointerException
06-28 09:57:11.720: E/AndroidRuntime(10569): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
06-28 09:57:11.720: E/AndroidRuntime(10569): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
06-28 09:57:11.720: E/AndroidRuntime(10569): at android.app.ActivityThread.access$600(ActivityThread.java:130)
06-28 09:57:11.720: E/AndroidRuntime(10569): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
06-28 09:57:11.720: E/AndroidRuntime(10569): at android.os.Handler.dispatchMessage(Handler.java:99)
06-28 09:57:11.720: E/AndroidRuntime(10569): at android.os.Looper.loop(Looper.java:137)
06-28 09:57:11.720: E/AndroidRuntime(10569): at android.app.ActivityThread.main(ActivityThread.java:4745)
06-28 09:57:11.720: E/AndroidRuntime(10569): at java.lang.reflect.Method.invokeNative(Native Method)
06-28 09:57:11.720: E/AndroidRuntime(10569): at java.lang.reflect.Method.invoke(Method.java:511)
06-28 09:57:11.720: E/AndroidRuntime(10569): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:810)
06-28 09:57:11.720: E/AndroidRuntime(10569): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:577)
06-28 09:57:11.720: E/AndroidRuntime(10569): at dalvik.system.NativeStart.main(Native Method)
06-28 09:57:11.720: E/AndroidRuntime(10569): Caused by: java.lang.NullPointerException
06-28 09:57:11.720: E/AndroidRuntime(10569): at com.touchscreentable.ThirdMenu.onCreate(ThirdMenu.java:43)
06-28 09:57:11.720: E/AndroidRuntime(10569): at android.app.Activity.performCreate(Activity.java:5008)
06-28 09:57:11.720: E/AndroidRuntime(10569): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
06-28 09:57:11.720: E/AndroidRuntime(10569): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
06-28 09:57:11.720: E/AndroidRuntime(10569): ... 11 more
再開するには、ボタン「b1」を押して「ThirdMenu」画面に移動すると、クラッシュします。「ThirdMenu」はタブ スワイプ アクティビティです。助けてください！