ViewPager的setAdapter上的NullPointer异常

Question

在一个屏幕中，我正在使用两个视图器 - 一个用于图像自动架，另一个用于按钮手工滚动。Image AutoScrolling运行良好，但是当我在ViewPager上添加了按钮的实现时，我的应用程序开始在SetAdapter上为NullPointer崩溃时，我正在使用FragmentPagerAdapter。对于图像自动剪裁器，我正在使用此参考代码https://github.com/jakewharton/android-viewpagerindicator

这是我的源代码

布局xml文件simple_circles.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
    <!-- android:layout_weight="0.01" -->
    <SearchView
        android:id="@+id/search_view"
        android:layout_width="fill_parent"
        android:layout_height="80dp" >
    </SearchView>
    <android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_width="fill_parent"
        android:layout_height="400dp">
    </android.support.v4.view.ViewPager>
    <android.support.v4.view.ViewPager
        android:id="@+id/pager_for_buttons"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" >       
    </android.support.v4.view.ViewPager>

用于在滑块上添加按钮的片段 -

    public class ScreenSlidePageFragment extends Fragment {
    public static final String ARG_PAGE = "page";

    private int mPageNumber;

    public static Fragment create(int pageNumber) {
        ScreenSlidePageFragment fragment = new ScreenSlidePageFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_PAGE, pageNumber);
        fragment.setArguments(args);
        return fragment;
    }
    public ScreenSlidePageFragment() {
    }
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mPageNumber = getArguments().getInt(ARG_PAGE);
    }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
         // Inflate the layout containing a title and body text.
        Button music_button = new Button(getActivity());
        music_button.setText("Music");
        Button news_button = new Button(getActivity());
        news_button.setText("News");
        Button videos_button = new Button(getActivity());
        videos_button.setText("Videos");
        Button photos_button = new Button(getActivity());
        photos_button.setText("Photos");
        LinearLayout layout = new LinearLayout(getActivity());
        layout.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
        //layout.setGravity(Gravity.CENTER);
        layout.addView(music_button);
        layout.addView(news_button);
        layout.addView(videos_button);
        layout.addView(photos_button);
        return layout;

    }

    public int getPageNumber() {
        return mPageNumber;
    }
}

ViewPager的活动类和适配器 -

public class SampleCirclesDefault extends FragmentActivity {
    // Initialization
    TestFragmentAdapter mAdapter;
    ViewPager mPager;
    PageIndicator mIndicator;
    Bitmap bitmap;
    ArrayList<String> bandImagesList;
    ImageView build_bandapp_img;
    boolean pagerMoved;
    Runnable Update;
    Handler h;
    long ANIM_VIEWPAGER_DELAY;
    Handler handler;
    int NUM_PAGES = 5;
    ViewPager buttonPager;
    ScreenSlidePagerAdapter buttonAdapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // No action bar
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
            **setContentView(R.layout.simple_circles);**
        build_bandapp_img = (ImageView) findViewById(R.id.imageView_for_webview);
        build_bandapp_img.setOnClickListener(new OnClickListener() {
            // Build bandapp button
            @Override
            public void onClick(View v) {
                Intent i = new Intent(SampleCirclesDefault.this,
                        BandDetailedActivity.class);
                startActivity(i);
            }
        });
        mAdapter = new TestFragmentAdapter(getSupportFragmentManager());// adapter
                                                                        // for
                                                                        // viewpager
        mPager = (ViewPager) findViewById(R.id.pager);
        mPager.setAdapter(mAdapter);
        buttonAdapter = new ScreenSlidePagerAdapter(getSupportFragmentManager());
        //buttonAdapter = new AdapterForFragmentOfButtonSlider(getSupportFragmentManager());
        buttonPager = (ViewPager)findViewById(R.id.pager_for_buttons);
        buttonPager.setAdapter(buttonAdapter); //***error -NullPointerException***//
        mIndicator = (CirclePageIndicator) findViewById(R.id.indicator);
        mIndicator.setViewPager(mPager);// dot dot indicator
        buttonPager.setCurrentItem(1); 
        handler = new Handler();
        // autoscrolling of view pager
        Update = new Runnable() {
            int currentPage = mPager.getCurrentItem();
            public void run() {
                if (currentPage == NUM_PAGES - 1) {
                    currentPage = 0;
                }
                mPager.setCurrentItem(currentPage++, true);
            }
        };
        Timer swipeTimer = new Timer();
        swipeTimer.schedule(new TimerTask() {
            @Override
            public void run() {
                handler.post(Update);
            }
        }, 100, 5000);
    }
     private class ScreenSlidePagerAdapter extends FragmentPagerAdapter {
            public ScreenSlidePagerAdapter(FragmentManager fragmentManager) {
                super(fragmentManager);
            }
            @Override
            public Fragment getItem(int position) {
                return ScreenSlidePageFragment.create(position);
            }
            @Override
            public int getCount() {
                return NUM_PAGES;
            }
        }
    }

堆栈跟踪

01-23 13:56:57.067: W/dalvikvm(18861): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
01-23 13:56:57.098: E/AndroidRuntime(18861): FATAL EXCEPTION: main
01-23 13:56:57.098: E/AndroidRuntime(18861): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.viewpagerindicator.sample/com.viewpagerindicator.sample.SampleCirclesDefault}: java.lang.NullPointerException
01-23 13:56:57.098: E/AndroidRuntime(18861):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at android.os.Looper.loop(Looper.java:137)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at android.app.ActivityThread.main(ActivityThread.java:5041)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at java.lang.reflect.Method.invokeNative(Native Method)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at java.lang.reflect.Method.invoke(Method.java:511)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at dalvik.system.NativeStart.main(Native Method)
01-23 13:56:57.098: E/AndroidRuntime(18861): Caused by: java.lang.NullPointerException
01-23 13:56:57.098: E/AndroidRuntime(18861):    at com.viewpagerindicator.sample.SampleCirclesDefault.onCreate(SampleCirclesDefault.java:85)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at android.app.Activity.performCreate(Activity.java:5104)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
01-23 13:56:57.098: E/AndroidRuntime(18861):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
01-23 13:56:57.098: E/AndroidRuntime(18861):    ... 11 more
01-23 13:57:13.356: I/Process(18861): Sending signal. PID: 18861 SIG: 9

我已经准确地指出了我的错误位置。

请帮助我解决此错误，谢谢。

Answer 1

yes it was because of different layout files

因此，如果buttonPager为null，则设置了一个没有buttonPager的布局。

这证实了我之前发表的评论。

  buttonPager = (ViewPager)findViewById(R.id.pager_for_buttons);
  buttonPager.setAdapter(buttonAdapter); 

也检查此

http://developer.android.com/training/animation/screen-slide.html