android - 嵌套ViewPager，调用其setCurrentItem方法失效

Question

今天在一个自定义的ViewGroup中嵌套了ViewPager，为了能显示ViewPager前后两页的内容，但是发现使用过程中，ViewPager的setCurrentItem无效了，始终都是从第0页开始显示，求大侠指导。

自定义ViewGroup代码如下：

public class PagerContainer extends FrameLayout implements ViewPager.OnPageChangeListener {
    private ViewPager mViewPager;
    private boolean mNeedsRedraw = false;

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

    public PagerContainer(Context context) {
        this(context, null);
    }

    public PagerContainer(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public PagerContainer(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initData();
    }

    private void initData() {
        // 允许子View在其区域内进行绘制
        setClipChildren(false);

        // child clip功能在Android3.x之后的版本会因为硬件加速而不起作用，所以这里需要关闭硬件加速功能
        setLayerType(View.LAYER_TYPE_SOFTWARE, null);
    }

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

    @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 event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mInitialTouch.x = (int) event.getX();
                mInitialTouch.y = (int) event.getY();
            default:
                event.offsetLocation(mCenter.x - mInitialTouch.x, mCenter.y - mInitialTouch.y);
                break;
        }

        return mViewPager.dispatchTouchEvent(event);
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        if (mNeedsRedraw) invalidate();
    }

    @Override
    public void onPageSelected(int position) {

    }

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

    public ViewPager getViewPager() {
        return mViewPager;
    }
}

布局如下：

   <com.yunos.ui.widget.PagerContainer
        android:id="@+id/pager_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#000000">

        <android.support.v4.view.ViewPager
            android:id="@+id/viewpager_layout"
            android:layout_width="200dp"
            android:layout_height="200dp"
            android:layout_gravity="center_horizontal"/>
    </com.yunos.ui.widget.PagerContainer>

MainActivity初始化代码：

    private void initView() {
        mPagerContainer = (PagerContainer) findViewById(R.id.pager_container);
        mViewPager = mPagerContainer.getViewPager();
        Log.e(TAG, "get viewpager current item=" + mViewPager.getCurrentItem());
        // 如下方法失效，求指导
        mViewPager.setCurrentItem(1);
        Log.e(TAG, "get viewpager current item=" + mViewPager.getCurrentItem());
        mViewPager.setOffscreenPageLimit(AppPageAdapter.NUM_ITEMS);
        mViewPager.setClipChildren(true);
        mViewPager.setPageMargin(15);
        mFragmentPagerAdapter = new AppPageAdapter(getSupportFragmentManager());
        mViewPager.setAdapter(mFragmentPagerAdapter);
    }

Answer 1

Oh, what an idiot, I looked at the source code of ViewPager about setCurrentItem and found:

        if (mAdapter == null || mAdapter.getCount() <= 0) {
            setScrollingCacheEnabled(false);
            return;
        }

You should call setCurrentItem after setAdapter. I have made this stupid mistake and I am speechless.

The question will not be deleted, but I will give you a warning to prevent similar mistakes!

Answer 2

mPagerContainer.setCurrentItem(1);

This is a line of error code. The container does not have a setCurrentItem method. It should be mViewPager.setCurrentItem(1);
setCurrentItem should be after setAdapter.

Answer 3

Whose currentIterm should mPagerContainer set? What is printed in the log is indeed mViewPager