android - 当我按按钮转到“滑动选项卡”菜单时，Android应用程序崩溃

Question

这是代码:

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);

        }

    });
}

当我按下图像按钮“b1”时，它崩溃了。这是我要浏览的“ThirdMenu”(Tab Swipe Activity ):

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;
    }
}

}

这是Android Manifest文件:

<?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>

这是logcat错误:

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

因此，当我按下按钮“b1”导航到“ThirdMenu”屏幕时，它崩溃了。 “ThirdMenu”是一个标签滑动 Activity 。请帮忙!

Answer 1

我认为(ViewPager)findViewById(R.id.pager)为空值