无法创建View Pager

Question

我想创建一个ViewPager，但是当我在手机中执行该应用程序时，它会显示一个空白活动，然后显示以下错误消息：

The application testViewPager (process com.example.testviewpager) has stopped unexpectedly. Please try again.

我该如何解决此问题？

---

main.xml中：

<?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">
    <com.example.testviewpager.PagerContainer 
        android:id="@+id/pager_container" 
        android:layout_width="match_parent" 
        android:layout_height="wrap_content" 
        android:background="#CCC">

        <android.support.v4.view.ViewPager 
            android:layout_width="150dp" 
            android:layout_height="100dp" 
            android:layout_gravity="center_horizontal" /> 

    </com.example.testviewpager.PagerContainer>
  </RelativeLayout>

PagerActivity.java：

    public class PagerActivity extends Activity {

    PagerContainer mContainer;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        mContainer = (PagerContainer) findViewById(R.id.pager_container);

        ViewPager pager = mContainer.getViewPager();
        PagerAdapter adapter = new MyPagerAdapter();
        pager.setAdapter(adapter);
        //Necessary or the pager will only have one extra page to show
        // make this at least however many pages you can see
        pager.setOffscreenPageLimit(adapter.getCount());
        //A little space between pages
        pager.setPageMargin(15);

        //If hardware acceleration is enabled, you should also remove
        // clipping on the pager for its children.
        pager.setClipChildren(false);
    }

    //Nothing special about this adapter, just throwing up colored views for demo
    private class MyPagerAdapter extends PagerAdapter {

        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            TextView view = new TextView(PagerActivity.this);
            view.setText("Item "+position);
            view.setGravity(Gravity.CENTER);
            view.setBackgroundColor(Color.argb(255, position * 50, position * 10, position * 50));

            container.addView(view);
            return view;
        }

        @Override
        public void destroyItem(ViewGroup container, int position, Object object) {
            container.removeView((View)object);
        }

        @Override
        public int getCount() {
            return 5;
        }

        @Override
        public boolean isViewFromObject(View view, Object object) {
            return (view == object);
        }
    }
}

PagerContainer.java：

public class PagerContainer extends FrameLayout implements ViewPager.OnPageChangeListener {

    private ViewPager mPager;
    boolean mNeedsRedraw = false;

    public PagerContainer(Context context) {
        super(context);
        init();
    }

    public PagerContainer(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public PagerContainer(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init();
    }

    private void init() {
        setClipChildren(false);
    }

    @Override
    protected void onFinishInflate() {
        try {
            mPager = (ViewPager) getChildAt(0);
            mPager.setOnPageChangeListener(this);
        } catch (Exception e) {
            throw new IllegalStateException("The root child of PagerContainer must be a ViewPager");
        }
    }

    public ViewPager getViewPager() {
        return mPager;
    }

    private Point mCenter = new Point();
    private Point mInitialTouch = new Point();

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        mCenter.x = w / 2;
        mCenter.y = h / 2;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        //We capture any touches not already handled by the ViewPager
        // to implement scrolling from a touch outside the pager bounds.
        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mInitialTouch.x = (int)ev.getX();
                mInitialTouch.y = (int)ev.getY();
            default:
                ev.offsetLocation(mCenter.x - mInitialTouch.x, mCenter.y - mInitialTouch.y);
                break;
        }

        return mPager.dispatchTouchEvent(ev);
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        //Force the container to redraw on scrolling.
        //Without this the outer pages render initially and then stay static
        if (mNeedsRedraw) invalidate();
    }

    @Override
    public void onPageSelected(int position) { }

    @Override
    public void onPageScrollStateChanged(int state) {
        mNeedsRedraw = (state != ViewPager.SCROLL_STATE_IDLE);
    }
}

MainActivity.java：

public class MainActivity extends Activity
{

    PagerContainer  mContainer;

    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mContainer = (PagerContainer) findViewById(R.id.pager_container);

        ViewPager pager = mContainer.getViewPager();
        PagerAdapter adapter = new MyPagerAdapter();
        pager.setAdapter(adapter);
        // Necessary or the pager will only have one extra page to show
        // make this at least however many pages you can see
        pager.setOffscreenPageLimit(adapter.getCount());
        // A little space between pages
        pager.setPageMargin(15);
    }

    // Nothing special about this adapter, just throwing up colored views for
    // demo
    private class MyPagerAdapter extends PagerAdapter
    {

        @Override
        public Object instantiateItem(ViewGroup container, int position)
        {
            TextView view = new TextView(MainActivity.this);
            view.setText("Item " + position);
            view.setGravity(Gravity.CENTER);
            view.setBackgroundColor(Color.argb(255, position * 50,
                    position * 10, position * 50));

            container.addView(view);
            return view;
        }

        @Override
        public void destroyItem(ViewGroup container, int position, Object object)
        {
            container.removeView((View) object);
        }

        @Override
        public int getCount()
        {
            return 5;
        }

        @Override
        public boolean isViewFromObject(View view, Object object)
        {
            return (view == object);
        }
    }
}